Car AC problem/symptom and question

[wh500special 2,411]

The AC in my ~2010 Ford Edge started blowing warm air this spring. I like driving with the windows open so chose to ignore it, but now my daughter is home from college and using the car so there’s motivation to do something about it. 
 

Last summer it did the same thing so I took it to a local (very competent) shop who sucked it out, checked for leaks, recharged the 134A to spec, and tested it.   That seemed to fix it for the most part, but periodically it would blow hot for a while then clear up and cool reasonably well.  So something was wrong that was only showing up periodically and not when they had it.  
 

They indicated it was actually overcharged quite a bit when they started messing with it, so it must have a history with a prior owner not getting hood cooling from it. 

 

For the last couple weeks I told my kid just not to use it and I’d look at it eventually.  Today was eventually. 

 

With the engine running and the AC running wide open in my 85 degree garage I am getting around 25 psi on the low side and about 325-350 psi on the high side.  At idle.  That seems high on the high side. Compressor stays on and isn’t kicking off due to overpressure, so maybe this is normal but it seems higher than most references call for. 
 

Revving the engine to 1500 RPM dropped the low side to 11 psi and increased the high to about 400psi.
 

I get cool air out of the vents, but not cold.  Measured 52F-55F using outside air (not recirc).  In the sun with the greenhouse this car has, that’s not really adequate to do much useful cooling. 
 

To see what happened and get another datapoint, I trickled in a little additional refrigerant and the dash temperature rose and the pressures went up a little bit (55F-60F/30psi/350-370psi). That suggested to me that I was going the wrong way so I called it quits there. I considered bleeding some out to get another datapoint, but i wanted to be able to sleep tonight.  
 

I did read that this particular car is pretty sensitive to refrigerant charge, so it could be off.  But adding up other factors (previously overfill, sporadic operation, etc) suggests it’s something else too. 
 

I watched the gauges when I shut the engine off, expecting to see the high and low sides equalize.   After about 15 minutes the low side was in the 100 psi range and the high was still above 200.   I may check it in the morning to see if they do eventually equalize.  I assume there’s nothing deliberate in the system to keep the fluid from moving around. 
 

I’m not an AC person, but this kind of smells like an expansion valve problem to me.  
 

It’s a cheap part ( <$50 ), doesn’t look too hard to get to, and I can borrow a recovery unit and vacuum pump from work so this is doable in my driveway for minimal cost.  But if those of you who know things think the valve is a low probability for its ailments, I can go back to my strategy of just opening the windows.
 

I guess it could be the filter too/instead, but the wide delta when the system is off probably is a clue. Evaporator could be clogged, but taking the dashboard out to get to it is not on my list of things I will do.  

Any thoughts on whether I’m on a reasonable path with the valve?

 

thanks,

Steve

 

 

[Blaine 25]

Your pressures suggest a restriction, a new expansion valve is where i would start. Sounds like it’s sticking. Being that the high side is well over 300, the compressor appears to be in good shape, or at least capable of making good pressure.

 

  I would still inspect the high side of the expansion valve for compressor debris which may have got caught at the expansion valve and has caused the restriction. 
 

  Sometimes you can hear a sticking expansion valve if you listen closely to the dash, idle up to around 1500rpm, and a lower blower speed so you can hear over top of it.
 

 Silent for a few seconds, then a few seconds of hissing in the dash accompanied with a brief gush of cooler air through the vents, then back to warm, and the cycle repeats. Yours sounds to be just stuck. 
 

 On the newer (i’m old so everything is newer now) small capacity systems, it can be rather easy to flood the evaporator with just a few ounces of being overcharged, so be careful not to overcharge it, and check or just replace the cabin air filter if you haven’t already. They are often overlooked.