AC blockage Ford Explorer 2003 equipped with DEATC & rear AC controls: My AC works fine for about one hour, then very little air is blown through the vents, even though the fan is working fine. After sitting for a while, the blockage is cleared (I am assuming that the evaporator is icing up) and the AC works fine. AC coolant pressure is within the acceptable limits. Any ideas?

 

If the evap is truly icing up, then it is likely due to a bad low pressure switch. The LP switch is supposed to cut power to the compressor clutch coil when the pressure drops low enough to cause icing of the evap. Low pressure can also indicate a low-freon condition (= leak), which would ruin the compressor if it kept running that way so it protects the compressor in that situation.

Before you go off and start parts-swapping, you should find out what the source of the problem is. Do you have a real set of AC gages (for high-side and low-side pressure)? If so put them on the system when it stops working and see what you have. Low side pressures under ~25 psi - with the compressor still running - indicate a problem, which is most likely the LP switch. If no gage set, then pull over, open the hood and look for ice on the lines to the evap. Also look for the compressor to never stop running. It will run constantly in hot weather, but will cycle at lower settings and in cooler weather. The LP switch controls that.

All of this may be a total waste as you say no air is blowing through the vents. That sounds more like a blockage than evap icing. Something loose int he vents causing an intermittent blockage?

HTH

-Dave

 

Actually, that sounds exactly like evaporator icing. After sitting, there's probably a big puddle under the evap drain. There really is nothing in the evaporator case that can totally block the airflow except for the evaporator freezing solid.
I'm not a fan of randomly tossing parts at a problem, but you can be almost sure the cycling switch has failed closed. It's a common failure mode for them. About $15.

 

Thanks for the feedback: I do not have “real” gauges, just the DIY one for low-pressure. The blockage issue exists both in the recirc and fresh air settings. Is there anyway to test the low pressure switch?

Mike

 

My AC operates ice cold (always), but after about 20mins. of driving I came to a stop and my 5.4 engine stalled while in drive.
It turned over: but the AC was NOT blowing cold. I kept the AC OFF on the way home, and when I got home it ON and operated fine, like normal. My truck is always doing weird stuff like that...2002 FORD EXCURSION. Any ideas?

 

This is one time where the fix is so cheap it isn't worth spending a ton of time diagnosing. The switch is like $12-15. Replace it and find out...

-Dave

 

Hey Dave!
Where is the switch located?
Got a mfg. number?
What do I call it? An AC switch?
I'd better get one, because it's starting to happen more often.
Just when it went down, later I heard the compressor click on...
WANT TO BE PREPARED FOR AUGUST IN VIRGINIA.
Thanks for the advise.
Later, Joe

 

It's the Low Pressure Cutout switch on the receiver/drier, which is the black or silver vertical cylinder on the passenger's side, near the firewall. There should be a 2-wire plug connected to it. Pull the plug and then unscrew the switch. There is a schrader valve behind it so it will only leak a squirt of freon before sealing up (unless the valve is stuck...)

...But I was responding to the OP. Your problem I do not know the answer to. This might be it, but I really don't have a clue based on what you've written so far. Could be a too-wide AC clutch gap, or something else. The stalling could be totally unrelated. Dunno

-Dave

 

Thanks. I'll take a look in the AM...
Joe

 

Thanks to all for the feedback: I swapped-out the low pressure A/C switch ( two min job) and I think the problem is solved (however I will no know for certain until I run the A/C unit for at least one hour). It appears that a “good” switch should have a slight rattle when shaken; whereas the old/non-operating switch has no rattle. This makes sense when you consider that a significant drop in pressure will close the switch, breaking the circuit to the compressor, and therefore the switch should have some play within its components to register the reduction in pressure.

 

I copied this data, I'm sure I have the same problem: And now have a solution. Thank you Dave, you really sound like you know your AC. And thanks to Osheam for sharing about that rattle sound. Please follow-up and let us know if this switch corrected the AC problem. This is so cool, no pun.~~~ Cost saving too. Thanks!

“Tell me and I’ll forget.
Show me and I’ll remember.
Involve me and I’ll understand.”
Confucius

 

Happy to help where I can. One thing you will find once you start learning about AC systems, is that they are really very simple.

Just give me tons o' rep, and I'll be happy :-)

Enjoy!

-Dave