AC Blows Cold Around Town But Hot On the Interstate

[GLOCKer]

I'm breaking this out into a separate thread until I figure it out.

1998 Explorer Limited 5.0 with the automatic climate control. When I set it to 60 degrees and high, I get ice cold AC, until I get on the interstate (and then it blows warm). Sometime after getting off the interstate (not long I think), it'll get cold again.

Any ideas? What can I try without getting into the pressurized part of the system, before I take it to a shop?

Ugh. I feel bad. I have family coming in on Thursday morning and I only have Wednesday between 4 and 6 pm to work on the truck before I have to drop it off for them to drive around in it. Sounds like they'll be having a hot time of it.

I also want to get it fixed not just for my comfort in the long run, but so I don't overheat my dogs!

 

[MAS Tequila]

Vacuum leak.

Check from the vacuum ball to the firewall for leaks.

I've been fighting them since I bought my 2000 Mounty.

The no vacuum default is to defrost.

Then when the engine rpms drop and the vacuum goes up, it can switch to the AC vents.

 

[BUXTER]

IIRC Heater Control Valve defaults to Open & goes to Closed via its Vac Diaphragm when AC is max cold - I'd check HCV Diaphragm first - U can watch HCV Close when selecting Cold Air in idle (Hi Vac situation) - Now whether its HCV or Vac Switch leaking in Low Vac situation (Hi speed) is the question - BTW U can throw a Tie Wrap on HCV & hold that puppy CLOSED.

 

[974X4BLACKSPORT]

Sounds like the evap. is freezing over when the pressure in the a/c gets lower from the faster turning a/c compressor when driving on the interstate. This usually happens when you are low on refrigerant. The water on the evap. freezes on the fins instead of running off and drop;ping to the road below and blocks the airflow.

 

[96eb96]

broken blend door? Plenty of fixes for that. Just search

 

[1998Exp]

By no means am I an A/C expert, but if this problem consistently happens while driving at higher speeds, regardless of engine load, even at very light throttle, I doubt it's vacuum related. You could probably verify with fast idle - something around 2000 RPM. If the problem occurs at fast idle, it's probably the A/C system itself, or perhaps the PCM getting confused by wrong input from something (Is the CEL on? Have you scanned for codes?) Take a look at the compressor clutch while at fast idle: is it engaged? If it's not, unplug the low side pressure sensor connector (on the accumulator dryer behind the firewall) and put a jumper wire across the two contacts. If the clutch now engages, could be a bad pressure sensor, low charge, or something confusing the PCM. You can force the clutch to engage by simply hoking battery voltage to it and taking it from there. Clutch engaged but still blowing warm: something wrong with the system, perhaps as simple as low charge (but that is usually indicated by fast cycling of the clutch while the system is still functional). To check the system you may need to go an A/C shop or invest in a manifold pressure gauge set - just $60 at Harbor Freight. Details of diagnosing by pressure readings are easy to find. If you can't, someone here will likely post the details.

 

[GLOCKer]

I think my blend door is working fine. Damn things switches over to great heat when you need it. From reading these posts, I have a lot to look at to try to chase this down. I feel bad (and miss my Explorer). My wife dropped it off at the airport for family to use flying into town early in the morning. I was hoping to have it fixed for them but I just don't have time.

 

[BUXTER]

I think my blend door is working fine. Damn things switches over to great heat when you need it. From reading these posts, I have a lot to look at to try to chase this down. I feel bad (and miss my Explorer). My wife dropped it off at the airport for family to use flying into town early in the morning. I was hoping to have it fixed for them but I just don't have time.

Took longer to Post that then it takes to put a Tie Wrap on HCV & hold it Closed - & It does default to Open, Closes w/ AC on Cold.

 

[rasouth]

I think it is a little ironic. My 2008 Honda Civic has the same problem. People I spoke with say it could be the clutch gap to the field coil is too wide. When power is supplied to field coil it engages the clutch and turns the compressor, but when it gets hot the gap widens and disengages. Not sure if it is the same process for the Explorer.

 

[GLOCKer]

Took longer to Post that then it takes to put a Tie Wrap on HCV & hold it Closed - & It does default to Open, Closes w/ AC on Cold.

I'll try that.

 

[GLOCKer]

I think it is a little ironic. My 2008 Honda Civic has the same problem. People I spoke with say it could be the clutch gap to the field coil is too wide. When power is supplied to field coil it engages the clutch and turns the compressor, but when it gets hot the gap widens and disengages. Not sure if it is the same process for the Explorer.

I'm hoping it's not this.

 

[boominXplorer]

Like stated earlier check pressures for low freon. Your freezing up in the evaporator. Could also be a stuck low pressure switch, stuck relay or stuck a/c clutch.

 

[CDW6212R]

Is the problem also with it in "Automatic", not the MAX position? MAX recirculates the air all the time, which will cause the freezing faster and more than the "Automatic" position. On the highway that has a bigger affect. So leave it on automatic until you know the freon is adequate.

I use mine on MAX most of the time, adjusting the temp to 70-74 as needed. That avoids the many smells outside, and I change it to automatic to allow some outside air in when it's been recirculating for a long while.

 

[koda2000]

When I use my A/C I always use it in the MAX position, which defaults to a temp display of 60 degrees F and directs the air flow to the dash vents. If you then change the heat/temp setting on the EATC you are no longer in MAX mode, which means you're not recycling the air. I could be wrong, but I think that's how it works.

Personally I don't like the EATC's automatic functions. When I want heat I want heat and when I want A/C I want it to be as cold as possible. The EATC display is cooler looking than the manual knobs though.

 

[CDW6212R]

The MAX position commands the air input from under the glove box, no matter what you adjust the temperature to. Adjusting the temperature then simply affects the fan speed. The fan will be on high until it sees cabin temps near the display number, thus adjusting it to 70 or so lowers the fan speed to a reasonable level, and lets it work automatically to hold that.

I wish there was simply a recirculate button, and I plan to install one eventually, on the bezel below there.

I prefer that because I want recirculation as much as possible, to keep outside smells from coming in. It's especially desirable at traffic lights, and when you spot old cars in front of you. Plus when you see a dead skunk on the road, you wish you had it on recirculate, or you push MAX fast and hope it's in time.

 

[boominXplorer]

Not to take this thread more off course but I'd love to have a/c clutch control (turn the compressor off in defrost mode) and a button to control the recirc door.

Also I'd love to have the controls setup like my 07 Focus. There is fan speed 0-4. On speed 0 the mode you have selected will stay on and if you turn recirc off you get air through the vents while driving. I love it for the winter time when I'm dressed warm as the air still flows through the heater core and keeps the car warm without turning the blower on. Turning the blower on 1 makes it too warm on hot and if I mix the air it feels almost cold if it's not set on hot when driving at speed.

Hard to explain but they are 2 totally differently designed systems and I favor the focus setup. If I could turn the a/c clutch off in defrost mode it would be perfect.

 

[GLOCKer]

So with the HCV, When I start the car it goes in. When I turn on the AC, it looks to stay in. When I shut off the car it goes back out. I'm assuming "in" is "closed"?

 

[boominXplorer]

Start the truck and turn your HVAC panel off. Leave it running and check the clutch. The clutch should now be disengaged correct?

 

[GLOCKer]

Start the truck and turn your HVAC panel off. Leave it running and check the clutch. The clutch should now be disengaged correct?

The AC clutch seems to be engaging and disengaging properly. I started it up and the AC was off and the clutch was disengaged. I put it to AC and the clutch engaged. I turned the EATC to 90 degrees and the clutch disengaged and the HCV opened up. I turned the EATC back to 60 degrees and Max AC and the HCV closed and the AC clutch engaged.

 

[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.