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2000 Limited AC blows warm when revving engine

ExploringOnTheEdge

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August 12, 2023
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City, State
Redding, CA
Year, Model & Trim Level
2000 Explorer Limited 5.0
Hi, I am at a loss to figure out this issue. My 2000 Limited edition Explorer blows cold only at idle, but as soon as I start accelerating, the air gets hotter the faster I go/the higher the engine speed. When it comes down to idle again, it doesn't immediately get cold; there's a long adjustment period. Let me give some background.

Early this summer, I took the vehicle in to a local mechanic for an A/C system inspection because the vehicle was having the issue I've described above. The shop found that there were metal fragments in the refrigerant loop that apparently came off the squash plate (due to detonation in the line, as the mechanic put it). These fragments were in the entire refrigerant loop, necessitating replacing everything under the hood for the A/C. After some deliberation, I made the decision to pay for the job although it was more than I paid for the vehicle 5 years ago (and 60,000 miles ago).

Everything was fine for a month or so. A/C blew cold at idle and speeding down the road. But a little while ago, the same problem appeared. I knew the A/C job had a 12 month warranty on it, so I took it back in and they found a leaking schrader valve and replaced that. When I picked up the vehicle from the shop and drove it home, I was very annoyed to find that the same problem was happening. A/C blowing cold at idle but getting progressively warmer as I accelerated.

So, I took it in again. They did a thorough job trying to track the issue down, or so they told me.. The determined in the end that the climate control module was bad and possibly the blend door actuator (as it had been exhibiting some slipping--plastic gears not as good as they used to be). Replacing the climate control module and blend door actuator will be another $1000, which I really don't want to throw at this vehicle without some strong assurance it will last for a while. They manually moved the blend door to a position to take all A/C (at least that's what they said they did), and then they removed the blend door actuator. The shop owner told me that at least it will work for the rest of summer, and I can decide what to do after that.

I was okay with this, except that when I drove it home from the shop, I noticed (AGAIN!) that it was exhibiting the same issue. Blowing cold at idle but as soon as I start driving down the street, it's getting warm and even hot. The auto shop thought they had fixed the issue, but if they simply driven it around the block, they would have discovered it wasn't fixed (both times!).

So, I started scouring the web (including this forum). I started to think it may be a vacuum issue. Apparently, the door for drawing air from the cab as well as the other vent doors and the heater control valve all operate on vacuum. I learned that as the engine accelerates, the vacuum manifold on the engine loses its vacuum. But that is why the A/C has a separate vacuum reservoir with a check valve inside of it. I found this spherical vacuum reservoir and verified that connecting the vacuum lines in one direction "worked" and in the other "didn't." When I disconnected it (to simulate losing vacuum at higher engine speeds), the air gets hot and just blows out of the defrost vents, which confirmed what I was reading online. Unfortunately, it didn't help me solve the issue I'm experiencing and I'm beginning to think it's not a vacuum issue. The air continues to blow out the panel vents when accelerating, but it's hot. I've confirmed that the heater control valve stays closed while accelerating as well.

Sorry for the book. I wanted to get all the context in one place. I'm really stumped on this one, so any help would be appreciated.
 



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Welcome to the forum! Too much info is far better than too little!

Do you have manual or automatic climate control (EATC)?

If you had a significant vac leak it might cause air to come out the defrost vents, but the blend door is (electrically) motorized. A vac leak (or faulty heater control valve) may cause the hot coolant to circulate through the heater core when it shouldn't. How did you determine that the heater control valve stays closed?

You currently do not have the blend door because they removed it, correct? If so, the only way it's going to blow heated air (opposed to hot only meaning it is ambient air temperature because the A/C isn't working properly) is if hot coolant is getting past the valve. Does the hose from the valve to the heater core feel hot when it's blowing hot air?

Does the A/C compressor clutch stay engaged (when set to cold) at higher than idle engine RPM? I mean besides full throttle in which case it should disengage.

Here's where it gets confusing to me. It seems like if the system is set to cool rather than heat, this should always completely close the heater core coolant valve. I mean why would you want heat put in the cabin at all if set to A/C? However I have read forum posts, and in the workshop manual, that with the system set to Max A/C, the valve is at full vac and closes, shutting off coolant flow to the heater core, BUT when the system is only set to A/C, not Max, the heater core valve has no vac, so it stays open to let hot coolant into the heater core. Why?

Anyway for the time being that is one thing I'd test, set it to Max A/C and see if this creates vac to, and if it operates the heater control valve to shut it.

I've attached the '99 Workshop Manual section on Climate Control. There are some troubleshooting steps in it, worth a look. The rest of the 2nd gen workshop manual is linked below in my sig, and the links in it mostly work unlike this conversion to PDF but you can scroll in the PDF instead to get to different sections.
 

Attachments







Thank you, J_C, for the thorough response.

I have automatic climate control, but for a long time I've always hit the "Max A/C" button when I want A/C turned on. Not sure if the temperature setting wasn't working for me before this year, but I never really used it.

I haven't tried feeling the heater coolant supply hose with the A/C on and checking it while running the engine at higher speed yet, but I did verify that the heater control valve is closed when set to "Max A/C". I fastened it in the shut position with zip ties and then revved the engine up higher and I still got warm/hot air out of the vents. The zip ties were unmoved and still intact, so I don't think the valve was able to open.

I haven't double checked the A/C compressor clutch or fan clutch operate as they should since the shop replaced those with all the work they did (they replaced the compressor, condenser, compressor belt, fan, fan clutch and basically the whole refrigerant loop under the hood).

I don't have an A/C button other than the max A/C so I imagine the only way I should be able to have the heater control valve open while the A/C is running is if it is in "Auto" mode, but as I explained above, I don't run it that way.

I really struggle to see how this could be a vacuum leak unless it was just leaking on a single line. Unless there is another vacuum line that is critical to the A/C function, I don't know how it could be a vacuum problem. The air recirculation door stays open while the engine is revving, by the way.

The workshop manual us a great resource, thank you! Is it mostly relevant for this year 2000 model?
 






If no hot coolant is getting to the heater core, the only remaining possibility "seems" like it is that the A/C is not working correctly to get the evap coil cold. You can see on that PDF, the basic setup on page 5. You should definitely check whether the compressor is cycling on, and staying on under higher than idle RPM, but of course it should cycle off and on to maintain the right pressure too, but if blowing hot, it should be cycled on.

The workshop manual spans a range of... I forget, maybe '96, to '99 and most things are going to apply to a '00 as well (I'd pick '99 to decrease the changes possible), but there's always some possibility they changed something between '99 and '00. AFAIK, most changes happened up to '99 and '00, '01 remained the same.
 






The blend door actuator and replacement eatc should not be 1000 job. Id say you probably have a blend door actuator problem that you can test with the eatc. The same test will tell you if there is anything wrong with the eatc but it will not tell if the actuators are leaking. Someone else might link but there is a good thread on the hvac system and troubleshooting thread here it’s a really good and worth looking over.

the suggestion on checking the heater valve is a good one, with the ac on max the lines to the heater core should not be hot. If they are replace that valve for sure.
 






Hi, I am at a loss to figure out this issue. My 2000 Limited edition Explorer blows cold only at idle, but as soon as I start accelerating, the air gets hotter the faster I go/the higher the engine speed. When it comes down to idle again, it doesn't immediately get cold; there's a long adjustment period. Let me give some background.

Early this summer, I took the vehicle in to a local mechanic for an A/C system inspection because the vehicle was having the issue I've described above. The shop found that there were metal fragments in the refrigerant loop that apparently came off the squash plate (due to detonation in the line, as the mechanic put it). These fragments were in the entire refrigerant loop, necessitating replacing everything under the hood for the A/C. After some deliberation, I made the decision to pay for the job although it was more than I paid for the vehicle 5 years ago (and 60,000 miles ago).

Everything was fine for a month or so. A/C blew cold at idle and speeding down the road. But a little while ago, the same problem appeared. I knew the A/C job had a 12 month warranty on it, so I took it back in and they found a leaking schrader valve and replaced that. When I picked up the vehicle from the shop and drove it home, I was very annoyed to find that the same problem was happening. A/C blowing cold at idle but getting progressively warmer as I accelerated.

So, I took it in again. They did a thorough job trying to track the issue down, or so they told me.. The determined in the end that the climate control module was bad and possibly the blend door actuator (as it had been exhibiting some slipping--plastic gears not as good as they used to be). Replacing the climate control module and blend door actuator will be another $1000, which I really don't want to throw at this vehicle without some strong assurance it will last for a while. They manually moved the blend door to a position to take all A/C (at least that's what they said they did), and then they removed the blend door actuator. The shop owner told me that at least it will work for the rest of summer, and I can decide what to do after that.

I was okay with this, except that when I drove it home from the shop, I noticed (AGAIN!) that it was exhibiting the same issue. Blowing cold at idle but as soon as I start driving down the street, it's getting warm and even hot. The auto shop thought they had fixed the issue, but if they simply driven it around the block, they would have discovered it wasn't fixed (both times!).

So, I started scouring the web (including this forum). I started to think it may be a vacuum issue. Apparently, the door for drawing air from the cab as well as the other vent doors and the heater control valve all operate on vacuum. I learned that as the engine accelerates, the vacuum manifold on the engine loses its vacuum. But that is why the A/C has a separate vacuum reservoir with a check valve inside of it. I found this spherical vacuum reservoir and verified that connecting the vacuum lines in one direction "worked" and in the other "didn't." When I disconnected it (to simulate losing vacuum at higher engine speeds), the air gets hot and just blows out of the defrost vents, which confirmed what I was reading online. Unfortunately, it didn't help me solve the issue I'm experiencing and I'm beginning to think it's not a vacuum issue. The air continues to blow out the panel vents when accelerating, but it's hot. I've confirmed that the heater control valve stays closed while accelerating as well.

Sorry for the book. I wanted to get all the context in one place. I'm really stumped on this one, so any help would be appreciated.
I believe you have vacuum issue.
The AC system is a closed system. Place thermometer in the center vent.
At idle , max setting , decir setting. Read the vent temp. If it in the low 40s at 70 degree outside temp. Adjust proportionately per outside temp. If you gauges install them look at the reading. I am assuming you don't.
If the vent temp fine. The AC system is fine. It a sub system problem. Like heater control valve, blend control door ( your is removed). When driving look at the vent temp if its close 195 degree the heater is on. If you have a vac gauge place on the heater control valve, see if you are missing vacuum. With the car not have moving , in park with engine running, Rev up the engine, and see what happens. Vacuum gauge, center vent temp. maybe the heater control valve is failing.
You stated you have a EACT module. That has inputs ambient temp sensor, in car temp sensor, sun unload sensor all share the same connection on EACT. Does blower work all the time (120f)? The module controls the AC clutch
 






A quick easy thing to check is the AC clutch. Mine was blued (hot spots on the metal) from slipping. The higher the rpm the harder it is for the clutch to engage and not slip.
We have three vehicles in our fleet. A 13 Honda Odyssey. A 14 Acura ILX. And a 98 XLT. We live in Phoenix, so the AC is going for half the year. And I've replaced the AC clutch on all of them.
You may see a few videos on YouTube suggesting you remove the little shims that set the spacing on the clutch. You can actually do this to adjust the air gap. But don't run without at least one.
 






I figured out the problem! After calling my mechanic again today, I learned a couple things. One, they had driven my explorer around the block to test out the AC after working on it and diagnosing the problem--which told me that it an issue that ALWAYS appeared when driving the vehicle. Two, the blend door (with the actuator removed) is free spinning on its axis. When the mechanic had moved it with his finger, he got cold air instantly out of the vents, indicating that this was the issue... either a bad blend door actuator or a bad EATC, but he also tested the EATC separately and found it to be problematic.

For some reason, whenever the shop guy took the vehicle for a drive, it never exhibited any issues, but immediately when I left the shop lot, the air coming out of the vents started to warm up. In any case, it makes sense now.

I suspect the blend door actuator has been having issues for a while. Before I took the vehicle into the shop the first time this year, I could hear the plastic gears slipping once in while (a clicking, almost popping sound). But it wasn't the real issue with the A/C as the refrigerant was trashed by then. When they replaced the whole refrigerant loop (minus the evaporator) in June, the A/C worked great and the blend door actuator limped along. At some point after that my EATC must have gone bad, and it couldn't keep the blend door in the "cold" position. Thus warm air started coming through the vents, especially when I revved the engine or accelerated down the road.

Another thing I learned is that, according to my mechanic, the heater control valve doesn't block all the hot coolant from entering the heater core, but only restricts the flow. I don't know if this is true per se, but I'm pretty sure the recirculation door has been working correctly, which means I wouldn't be pulling outside air in. I wonder if it would do anything to swap out the heater control valve for a simple temperature / pressure rated ball valve. I could restrict flow of the hot coolant to the heater core and maybe get even icier A/C! Not sure if this would be problematic for the engine though. Is that heater coolant loop part of a single closed loop for the engine coolant, or just a secondary loop?

This also confirms that I don't have a vacuum issue. I removed the A/C vacuum reservoir and confirmed that there was an internal check valve that was working by connecting the vacuum tubes in the opposite configuration and observing the air going to the defrost vents.
 






The blend door actuator and replacement eatc should not be 1000 job. Id say you probably have a blend door actuator problem that you can test with the eatc. The same test will tell you if there is anything wrong with the eatc but it will not tell if the actuators are leaking. Someone else might link but there is a good thread on the hvac system and troubleshooting thread here it’s a really good and worth looking over.

the suggestion on checking the heater valve is a good one, with the ac on max the lines to the heater core should not be hot. If they are replace that valve for sure.
Yeah, I have to wonder about the $1000 quote as well, but it seems everything is so expensive today. They charged me $2600 (more than I paid for the vehicle 5 years / 60,000 miles ago) to replace the A/C compressor, condenser, refrigerant lines, fan clutch, fan, belt, and probably some coolant lines. After all my conversations with the shop owner, I have to say I trust his word, and I do think he knows his stuff. In the end, he led me to the solution, and he'd be happy to troubleshoot over the phone more with me, I dare say.

He mentioned I could go to a junkyard and look for a used EATC, which I might do after it cools off some and I can even imagine wanting heat again.
 






I figured out the problem! After calling my mechanic again today, I learned a couple things. One, they had driven my explorer around the block to test out the AC after working on it and diagnosing the problem--which told me that it an issue that ALWAYS appeared when driving the vehicle. Two, the blend door (with the actuator removed) is free spinning on its axis. When the mechanic had moved it with his finger, he got cold air instantly out of the vents, indicating that this was the issue... either a bad blend door actuator or a bad EATC, but he also tested the EATC separately and found it to be problematic.

For some reason, whenever the shop guy took the vehicle for a drive, it never exhibited any issues, but immediately when I left the shop lot, the air coming out of the vents started to warm up. In any case, it makes sense now.

I suspect the blend door actuator has been having issues for a while. Before I took the vehicle into the shop the first time this year, I could hear the plastic gears slipping once in while (a clicking, almost popping sound). But it wasn't the real issue with the A/C as the refrigerant was trashed by then. When they replaced the whole refrigerant loop (minus the evaporator) in June, the A/C worked great and the blend door actuator limped along. At some point after that my EATC must have gone bad, and it couldn't keep the blend door in the "cold" position. Thus warm air started coming through the vents, especially when I revved the engine or accelerated down the road.

Another thing I learned is that, according to my mechanic, the heater control valve doesn't block all the hot coolant from entering the heater core, but only restricts the flow. I don't know if this is true per se, but I'm pretty sure the recirculation door has been working correctly, which means I wouldn't be pulling outside air in. I wonder if it would do anything to swap out the heater control valve for a simple temperature / pressure rated ball valve. I could restrict flow of the hot coolant to the heater core and maybe get even icier A/C! Not sure if this would be problematic for the engine though. Is that heater coolant loop part of a single closed loop for the engine coolant, or just a secondary loop?

This also confirms that I don't have a vacuum issue. I removed the A/C vacuum reservoir and confirmed that there was an internal check valve that was working by connecting the vacuum tubes in the opposite configuration and observing the air going to the defrost vents.
The heater coolant loop IS part of a single closed loop for the engine coolant. There is a heater core in the dash plastic.
 






I figured out the problem! After calling my mechanic again today, I learned a couple things. One, they had driven my explorer around the block to test out the AC after working on it and diagnosing the problem--which told me that it an issue that ALWAYS appeared when driving the vehicle. Two, the blend door (with the actuator removed) is free spinning on its axis. When the mechanic had moved it with his finger, he got cold air instantly out of the vents, indicating that this was the issue... either a bad blend door actuator or a bad EATC, but he also tested the EATC separately and found it to be problematic.

Previously I was led to believe that the blend door was removed. This is not the case? If the blend door is still there, gravity may make it flop down into the hot position, putting air through the heater core. I don't quite understand this situation, why wasn't the blend door actuator tested and replaced if found faulty? If as you wrote, the gears are stripped, that might be the only thing that needs done.

At some point after that my EATC must have gone bad, and it couldn't keep the blend door in the "cold" position. Thus warm air started coming through the vents, especially when I revved the engine or accelerated down the road.

It is possible the EATC has a vac leak, or a line to or from it does, so under high vac at idle it works, BUT this does not control the blend door. The blend door should work equally well regardless of engine RPM. Something is not adding up. You can check for voltage getting to the blend door actuator connector (momentarily, not constant) when it is changed from hot to cold and vice versa.

Another thing I learned is that, according to my mechanic, the heater control valve doesn't block all the hot coolant from entering the heater core, but only restricts the flow. I don't know if this is true per se, but I'm pretty sure the recirculation door has been working correctly, which means I wouldn't be pulling outside air in. I wonder if it would do anything to swap out the heater control valve for a simple temperature / pressure rated ball valve.

Why do that when you can instead, simply replace the heater valve with what it is supposed to have? I don't think it is correct that it only restricts the flow, when the system is set to Max A/C.

I could restrict flow of the hot coolant to the heater core and maybe get even icier A/C! Not sure if this would be problematic for the engine though. Is that heater coolant loop part of a single closed loop for the engine coolant, or just a secondary loop?

The heater loop is part of the closed loop, but it is not needed besides to operate the heater. It would cause no problem to plug off the heater core hoses if you don't need heat in winter. Engine works the same either way, just reaching the thermostat trip point a little earlier then thermostat opens and it's no longer a closed loop.


This also confirms that I don't have a vacuum issue. I removed the A/C vacuum reservoir and confirmed that there was an internal check valve that was working by connecting the vacuum tubes in the opposite configuration and observing the air going to the defrost vents.

This only confirms that you don't have a leak going to the mode door, which was already known since it wasn't stuck only blowing out the defrost vents. I have forgotten, did you check to confirm that the heater core valve is operating, that it is moving and keeping the heater core hoses from getting hot when set to Max A/C? If they are getting hot set to Max A/C, either the vac line to the valve isn't getting enough (if any) vac, or the valve is bad.

It might be time to smoke test the system to see if there are leaks. They could even be in the EATC module and that's why the shop is telling you that it is bad, but frankly I think the shop doesn't know what they are doing because with more eyes on it and their knowing what work has already been done, they should at least have determined whether the heater valve and the blend door were working even if they didn't bother to track down the vac leak. Possibly they did test and found no power getting to the blend door actuator, but then the conclusion should have been to set the actuator to the cold position and leave it installed... no point in removing it if not being replaced with another one.
 






The heater coolant loop IS part of a single closed loop for the engine coolant. There is a heater core in the dash plastic.
Good to know, and that seems to back up what my mechanic told me in that he said the heater control valve always lets some coolant through, even when closed.
 






Previously I was led to believe that the blend door was removed. This is not the case? If the blend door is still there, gravity may make it flop down into the hot position, putting air through the heater core. I don't quite understand this situation, why wasn't the blend door actuator tested and replaced if found faulty? If as you wrote, the gears are stripped, that might be the only thing that needs done.
I believe I stated that they removed the blend door actuator and only manually adjusted the blend door's position--it swings on a vertical axis. What with the weight of the blend door and movement of the vehicle, it appears to swing on its own when decoupled from the blend door actuator, and possibly favors the warm air side or at least sits in the middle.

It is possible the EATC has a vac leak, or a line to or from it does, so under high vac at idle it works, BUT this does not control the blend door. The blend door should work equally well regardless of engine RPM. Something is not adding up. You can check for voltage getting to the blend door actuator connector (momentarily, not constant) when it is changed from hot to cold and vice versa.

They tested the EATC by factory resetting (removing some fuse for a certain period of time, and perhaps with a Ford tool) and it didn't fix the issue, nor did swapping in a new blend door actuator fix the issue after the factory reset of the EATC. The shop concluded that the issue is at least with the EATC in commanding a position for the blend door, and possibly the blend door as well (mostly due to the fact that we've both heard the gears slipping). He didn't seem to think anything was wrong with the vacuum lines running to and from the EATC. They may have tested them. My own simple verification of removing vacuum and reconnecting the lines to the A/C vacuum reservoir backwards did not produce anything like the problem I've been experiencing. It simply caused all the air to blow out of the defrost vents.

Why do that when you can instead, simply replace the heater valve with what it is supposed to have? I don't think it is correct that it only restricts the flow, when the system is set to Max A/C.

I forgot to state in the beginning that I replaced the heater control valve earlier in this year (March) because I suspected it was just failed open or had a hole in it. It didn't fix the issue completely, though at the time I thought it helped a little. Not sure know whether the previous heater control valve was bad or not.

The heater loop is part of the closed loop, but it is not needed besides to operate the heater. It would cause no problem to plug off the heater core hoses if you don't need heat in winter. Engine works the same either way, just reaching the thermostat trip point a little earlier then thermostat opens and it's no longer a closed loop.

Well, I got the idea from Pete Deering's reply that it would be a problem to close that line of completely. But if the coolant has a circulation route outside of that line, then it should be possible to isolate the heater core. I guess it's working well enough now that that is not necessary--it's blowing cold air all the time now.

This only confirms that you don't have a leak going to the mode door, which was already known since it wasn't stuck only blowing out the defrost vents. I have forgotten, did you check to confirm that the heater core valve is operating, that it is moving and keeping the heater core hoses from getting hot when set to Max A/C? If they are getting hot set to Max A/C, either the vac line to the valve isn't getting enough (if any) vac, or the valve is bad.

So, it could be possible that there is a small vacuum leak that is inhibiting the heater control valve (possibly other vacuum actuators) to hold position, and I haven't yet felt the heater line behind the heater control valve to verify it's not hot while the Max A/C setting is on. If my mechanic is right, that some coolant always slips through this valve, then it makes sense that it would heat up after some time. It would be interesting to check this, and I'm curious whether the mechanic is right in saying that the heater control valve never full blocks flow even in the closed position.

It might be time to smoke test the system to see if there are leaks. They could even be in the EATC module and that's why the shop is telling you that it is bad, but frankly I think the shop doesn't know what they are doing because with more eyes on it and their knowing what work has already been done, they should at least have determined whether the heater valve and the blend door were working even if they didn't bother to track down the vac leak. Possibly they did test and found no power getting to the blend door actuator, but then the conclusion should have been to set the actuator to the cold position and leave it installed... no point in removing it if not being replaced with another one.

If the heater lines aren't getting hot while the system is running Max A/C, I don't see how there would be an issue with the vacuum. All the other buttons work correctly and send air to the vents they are supposed to. In addition, once I was able to lock the blend door in position, the air flow out of the front panel vents was a bit more forceful suggesting that somehow that flow was leaking somewhere when the blend door could freely move, or perhaps it was just pressure drop through the ducting with the blend door in a middle position.

I've gone back and forth but in the end I really trust this mechanic. He hasn't tried to upsell me on anything I don't need. He's probably spent 2-2.5 hours on the phone with me over this issue. He's even talked me through the next steps I could do to fix the problem on my own.
 






The heater loop is part of the closed loop, but it is not needed besides to operate the heater. It would cause no problem to plug off the heater core hoses if you don't need heat in winter. Engine works the same either way, just reaching the thermostat trip point a little earlier then thermostat opens and it's no longer a closed loop.

I should clarify my poor wording above. I meant plug off the hoses to keep the heater core and valve sealed from the elements. Where they attach to (and are then removed from) the engine, put in a new piece of hose that bends to connect the two together.
 






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