AC Blows Cold Around Town But Hot On the Interstate

[boominXplorer]

I'm going to say stuck low pressure switch since the system works but isn't cutting off when it should.

You can change it without discharging the system, there's a Schrader valve behind it.

 

[GLOCKer]

Also, we put the truck on a refrigerant fill/recovery machine this past summer and it was fine. Figured I should add that info.

I'm going to say stuck low pressure switch since the system works but isn't cutting off when it should.

How is that supposed to work? It seems like it's cutting off and not coming back on?

 

[boominXplorer]

How is that supposed to work? It seems like it's cutting off and not coming back on?

If the system runs constantly on the interstate with airflow through the condenser it will bring the low side of the system below 20lbs creating iceing. Once that starts you can have a block of ice in the dash but it will still come out luke warm as the air isn't passing through the fins. Once you slow down and stop and go a few times temps rise enough to melt it and it returns to working.

Take a ride on the interstate, make it stop working then pull over and look for ice on the expansion tank or pipes to evaporator.

 

[GLOCKer]

If the system runs constantly on the interstate with airflow through the condenser it will bring the low side of the system below 20lbs creating iceing. Once that starts you can have a block of ice in the dash but it will still come out luke warm as the air isn't passing through the fins. Once you slow down and stop and go a few times temps rise enough to melt it and it returns to working.

Take a ride on the interstate, make it stop working then pull over and look for ice on the expansion tank or pipes to evaporator.

The next time I get out on the interstate I'll check on that. I'd characterize what comes out more than lukewarm though.

Typically how long do you need to be running before this happens?

 

[GLOCKer]

Here's a video I just shot of the compressor running with and without throttle.

 

[GLOCKer]

Please be patient with me as this AC stuff is a little out of my comfort zone.

So if I'm getting icing, it's most likely a bad low side pressure switch? I believe someone mentioned that the switch is easily replaced because it is sealed with a valve where it connects in? So this means it something I could potentially handle myself without a shop having to do it. If I end up with the described icing, is this the switch I need to replace? https://www.napaonline.com/en/p/ECHRPS622?searchCategory=12.7&searchIndex=App

Thank you guys for your help trouble shooting this so far. I'm hoping to get out sometime tomorrow to run this thing up to speed to check for icing.

 

[CDW6212R]

Being low on freon is the common cause of icing. Similarly, the pressure on the low side drops(and drops more) when there is too little freon, the LPS is what shuts down the compressor until the pressure comes back up(happens naturally with the compressor off(equalizes)).

I gather that many LP switches have an adjustment screw down in them, which you can alter. AN AC expert should be consulted to know what the cut off pressure is, it's different for R11 versus R134 for example.

So you might have a slow freon leak, thus low freon. The quick connections are the prime suspect for freon leaks, the OEM spring steel clamps they put on don't do a great job of stopping vibration there. There are aftermarket aluminum clamps which are more stronger(they are rigid when installed). I've used those several times on older Fords, I put a couple on my Mercury in about 2004. I've forgotten about those, I need to get some for my current cars.

 

[koda2000]

A/C:
I totally agree with @CDW6212R. It's likely you either have low refrigerant and/or your low pressure switch is cutting off the compressor. I also agree that the most common place for refrigerant to leak is from the ports. On older vehicles the plastic caps may be missing or they are not doing a good enough job of sealing the ports. If you can find metal caps they're a better choice, but you need to at least have good plastic caps and they need to be tight. Your truck is 21 years old. It might just need a little refrigerant. A/C systems are like tires, in that they all lose a little pressure over time.

If you don't have a set of A/C gauges (around $60 from Harbor Freight) and don't want to purchase a set, I think you should take your Expl to an A/C shop and at least have your pressures checked.

Windows:
As all the windows get their power and grounds to function through the driver's master switch, if there are connection or contact problems with the master switch you can have all kinds of problems. When I first got my '01 ST the only window that worked correctly was the driver's window. All the interior door panels had been removed, the passenger side front window would not work at all, the passenger side rear would go down from it's switch, but not up. It would go up from the master switch but not down. The driver's rear door had been completely gutted by the PO. Before I attempted any repairs, using my battery charger and 2 nails (poor man's Power Probe) I tested the 2 passenger side window motors from their 2 motor wires (they went up/down just fine). Next I examined the driver's door wiring bundle and found no broken wires. Lastly (after making a map of the wire colors to each door) I ran power and ground to passenger side windows via the master switch's electrical connector and they worked fine. I also checked that I had power and ground going to the gutted door's wiring. That left nothing to be at fault but the master switch. I bought a new $22 master switch off eBay, reconstructed the driver's side rear door window regulator and other missing/broken parts with used parts. When the new master switch arrived I installed it and everything worked. That was 4 years ago and I've had no window issues since. It amazes me that the PO took so much apart and did so much damage assuming he had simultaneously developed 3 bad window motors. I think that (and a bad fuel pump) were the only reasons he gave the truck away to someone he owed some money to. BTW - The heat and A/C didn't work either. I fixed both for about $5 in used parts, and by reconnecting a vacuum hose to the HCV and the A/C's HIGH pressure switch.

I don''t believe in throwing parts at a problem without being very sure the part will solve my problem (I'm cheap and have lots of time to do proper diagnostics). If you're a Gold Rush fan, you might recall what a younger Parker was told when he asked Tony Beets "how do you know if there's gold in the ground?" Tony's response was "drill holes, drill holes, drill holes",

 

[boominXplorer]

Please be patient with me as this AC stuff is a little out of my comfort zone.

So if I'm getting icing, it's most likely a bad low side pressure switch? I believe someone mentioned that the switch is easily replaced because it is sealed with a valve where it connects in? So this means it something I could potentially handle myself without a shop having to do it. If I end up with the described icing, is this the switch I need to replace? https://www.napaonline.com/en/p/ECHRPS622?searchCategory=12.7&searchIndex=App

Thank you guys for your help trouble shooting this so far. I'm hoping to get out sometime tomorrow to run this thing up to speed to check for icing.

Yes you can change the low pressure switch out without decharging the system.

 

[GLOCKer]

Ughhhhh. A little frustrated today. I took the Explorer out to run up the AC and then get on the interstate. The ACt didn't get impressively cold today. It was just mildly cold coming out of the dash. No notable changes on the interstate either; it didn't really gt any warmer. When I stopped there appeared to be no ice anywhere nor any dripping off the bottom after a couple of minutes of sitting.

 

[CDW6212R]

How long does the compressor run while idling at normal temps? As the freon gets low, the run time is much less, and the down time is much greater. It sounds like it is at least a bit low on freon.

 

[GLOCKer]

I ran to the Advanced Auto on the corner and bought a can of R134 with a pressure gauge on it. As soon as I hooked it up the pressure gauge shot to FULL. Luckily they let me return the can because I didn't use it.

So now what? Low Pressure Switch? What are the chances it's the orifice tube?

 

[koda2000]

Sounds like you may have too much refrigerant rather than not enough, but the gauge on a can of auto parts store's refrigerant is not enough to tell you whats going on. There are several factors that go into measuring the correct amount of refrigerant in a system and whether your system is working correctly. To do it properly you need a set of A/C gauges connected to the high and low pressure ports and you need to take into account ambient temperature and humidity.

 

[boominXplorer]

I ran to the Advanced Auto on the corner and bought a can of R134 with a pressure gauge on it. As soon as I hooked it up the pressure gauge shot to FULL. Luckily they let me return the can because I didn't use it.

So now what? Low Pressure Switch? What are the chances it's the orifice tube?

Did the gauge read full while the truck was running and ac was on max?

 

[GLOCKer]

Did the gauge read full while the truck was running and ac was on max?

Yes. I started the truck and put the AC to MAX AC. Then I removed the plastic cap from the low side port (on top the dryer). As soon as I snapped the hose on the gauge shot to the green "full" zone.

 

[Mbrooks420]

Don’t these pressures vary quite a bit with ambient outside temp?

 

[koda2000]

Too much pressure on the low side could (could) mean a blockage. Perhaps a clogged orifice tube. If it's a clogged orifice tube it might be that you compressor is failing and pushing fragments through the line.

Note the screening on the tube. That's what would trap any debris. If it get's clogged the debris had to come from somewhere and the compressor is the most likely suspect.

The orifice tube acts as filter and the expansion valve. It's the dividing line between the high and low sides.

It would be helpful to know what the high side is doing.

I have a small hand-held A/C pressure tester. I find that with a good working A/C system with an adequate charge the gauge usually registers around 30 PSI w/engine running, A/C on. This is not a very good test though (much like the gauge on the auto parts store's refill can)

 

[koda2000]

Don’t these pressures vary quite a bit with ambient outside temp?

Yes. I said this earlier.

 

[Mbrooks420]

My point is the can gauge may not be accurate depending on outside temp.

 

[koda2000]

My point is the can gauge may not be accurate depending on outside temp.

It's not that warm in GA right now (70's-low 80's), so I think the outside temp effect would be negligible. My point is you need a set of A/C gauges to really know what's going on.