Hi all..
I have a 06 expedition limited and have been having a ac problem for some while now.. Around town both front and rear ac work and blow cold air just fine. While on the hwy 20-30 miles on road outside temp 90+,ac starts to fade, on high you can barely feel it coming out of the vents but it's still loud... Evaporator is freezing up..after a hour plus of hwy driving the rear will slowly fade away also..I can turn off the ac off and around 5 minutes turn it back on and the ac will work good for around 15 or so minutes before fading away again. Had the ac checked out,no leaks,not low on freon. Suggested the front expansion valve be changed..tried that and still same problem..temp monitored from the vent gets as low as 28-30 degree F before fading away?? Any suggestion greatly appreciated..

 

What you describe is caused by the evaporator getting too cold and freezing the condensation on it.
The evaporator pressure/temperature is controlled by the cycling switch. It's supposed to turn the compressor off at 29psi on the low side, which equates to about 33 degrees evaporator temp.
It's very likely the switch is cutting out at a lower temp or not at all, the shop should have checked this. They also replaced the "front expansion valve" on a vehicle that doesn't have one. The front uses a fixed orifice tube.

Replace the Cycling Switch (aka:Low Side Pressure Switch) and you should be fine. Just unscrew the old one and screw the new one on.
Also, think about finding another shop.

 

I'll get the cycling switch and try that. I bought the expansion valve/block from autozone for this specific vehicle so I figured it had one? 2006 expedition limited.. Thanks..

 

Oops, I was mistaken. The 07 does have the block on the front AC. I was thinking of the earlier system. My apologies.

 

Is this switch the one on the top left up front when you open the hood??

 

Just fould out that on expansion valve system all the low pressure switch is For not keeping the compressor running if the refrigerant gets low.. On orfice tube systems it keeps evaporator from freezing up

 

That's correct, no cycling switch with the expansion valve.
With a non equalized TXV without a sensing bulb in the evaporator, the only thing I know of that "might" cause your problem is a slight refrigerant under charge. Likely about 2-3 ounces.

It's possible that the system has a sensor in the evaporator that signals the PCM to shut down the compressor if the evaporator starts to ice up. I don't have the service info for your truck, though.

 

Thanks isrx101.. I spoke shortly with a ford tech and he suggested I have the Evaporator discharge air sensor checked out.. I made sure it was connected and it appears to be in good condition upon prying it out of the box. I can have ford hook it up and scan/run a test to see if it functions right but I'll prolly just replace it.. Around $50 might be cheaper this way..your thoughts?? Thanks!!

 

hey ndogg,did u find a solution to your ac issue?????? MY 2006 just started to do the same.

 

Yes finally!!! It was the evaporator discharge air sensor as mentioned above. It cost $51 at the ford dealership anymore questions you can email me at ndogg3539@aol.com

 

That was the whole reason they put that sensor in there. The earlier models had the freezing up issue and had to be modified. Glad you figured it out!