Hey guys, I've got a 2000 X Limited. It's got a V-10 and dual zone HVAC with manual A/C controls (no EATC) on the dash. I was driving home the other day with the A/C on, and as I pulled in my driveway a wasp landed on the dash right above the steering wheel. I smacked it pretty good with a paperback book (sorry animal lovers), and about 2 seconds later got a whiff of something electrical....uh oh. I did a quick check and couldn't find anything hot, burning, defective etc, so I shut it off and went in. That afternoon when I went to go somewhere else, now the A/C isn't cold--front or rear air either one. Both blowers work fine, the plenum controls work correctly, just no compressor kicking on to give me cold air front or rear.

I jumped the low pressure cutoff and the compressor clutch cycled on correctly. I had an extra "known good" dash control **** assembly so I swapped it out, still no cold air. I don't have any A/C gauges to check if it's low on freon, but with the way it was previously VERY cold coupled with the electrical smell when I smacked the dash has me thinking something electrical smoked, not low freon.

The A/C fuse in the dashboard fuse box is good, the A/C diode out in the engine compartment Power Distribution box is good...as I researched the problem for solutions I've seen a couple posts mention an "A/C circuit board", possibly somewhere in the passenger dash area? I flipped out the glove box to check in the under-dash area, took the radio out and looked behind it, looked all around the A/C plenum box in the passenger footwell...I don't see anything obvious, but then I'm not sure what (if anything) I'm even looking for.

Anybody experience anything like this or know of additional electrical components in the cabin besides the **** assembly that would control the compressor operation? Or is it just coincidental that I smacked the dash at the EXACT moment my low pressure switch failed or my freon reached a critical level LOL

Thanks!

 

That would be one heck of a coincidence if it is AC issues are always a real bummer. Hope you get it dicked quickly.
WELCOME to the world of XXXs by the way.

 

Well you already isolated the problem to be at the low pressure switch. If jumping it started the compressor, then it is either bad or reading a low pressure condition. Confirm the pressures and/or replace the switch.

 

Well....assuming there is nothing else electrically controlling the compressor in parallel with the low pressure switch, that would be right. That's why my question was, does anyone know if there is another electrical component (the aforementioned "A/C circuit board somewhere in the passenger dash area" from a couple of different posters) that also controls the compressor operation in parallel with the LP cutoff switch?

I'm not clear on your response -- does it mean you've had this problem or are knowledgeable about the Excursion's A/C circuit KNOW there's not another electrical component and it's definitely the low pressure switch, or are you assuming it's the LP switch just because I jumped it and it came on? Electrical components are easy swaps, just disconnect the battery and have at it....but replacing the LP switch requires opening the closed loop freon system, something I'd rather not do unless I'm SURE it's the problem. Thanks for the reply!

 

I cant find the wiring diagrams right now but basically you get a signal from the controls that goes through the circuit to the compressor clutch solenoid. This circuit contains the high and low pressure switches in series. Both have to be closed to activate the clutch. You took the lp switch out of the circuit with the jumper. It completed the circuit and the compressor ran.
You also told us that the controls worked correctly.
Therefore, my interpretation was that the only change that was made was bypassing the low pressure switch. This indicated to me that there is either a bad switch, bad connection at the switch, or the pressure in the system is too low to close the switch.
The low pressure switch should be able to be replaced without evacuating the system. The end going to the refrigerant side has a connection similar to a tire valve. You should only get a short burst out of it when removed.
There should also be an input to the circuit from the PCM but that should be working based on the fact that it works when jumping the switch.
Sorry for the confusion and if I am not explaining myself fully. I am writing this based on my memory of previous troubleshooting.

 

And, you need something like 25 psi for the low pressure switch to complete.

 

The "electrical smell" turned out to be a red herring. I got a day off work and finally got around to hooking up the manifold gauges....truly low on freon. I traced the problem to the O-rings where the A/C line goes into the dryer--a slow but steady leak. Upon closer inspection I noticed the line was bent, almost as if somebody working on the engine had leaned on the lines? I straightenend the line and put new O-rings in, then vacuumed the system down and let it sit an hour....came back and it was still holding steady. Refilled the freon and it's back to freezing me out. Thanks for the info, especially about the low pressure switch. I've never had to change one yet, just assumed they would open the system once removed....it's nice to know that if it ever DOES fail, I can easily replace it :-)

 

Good work. How high did you charge it ?
Mine is cold but not freezing cold. Takes a bit to become comfortable.

 

The ambient air temp was 91....I had my wife hold it at a steady 1300 RPM and had the fan switch set one notch below high. With the compressor running, I added until the low pressure reading was about 32 and the high pressure reading was about 220. My output air is now 44 degrees.

Your output air temp at the vent will vary based on the actual air temp, but generally speaking an efficient running system will cool the air about 40-50 degrees below the ambient air temp. Expect a little less on humid days, because the system has to remove extra moisture besides cooling the air. Checking and adding refrigerant, you have to make sure and get the right amount in--and that also varies according to the outside air temp. Too much refrigerant is as bad as too little--too much increases the system pressure and puts extra stress on the compressor...too little doesn't let enough lubricant circulate and can also damage your compressor. And remember that above the recommended level...besides being hard on the compressor, the warmer your output air will get. That is because refrigerants follow a pressure temperature curve, and the low side pressure reading is basically the pressure at the fixed orifice tube. The higher the pressure above recommended, the less efficient the orifice tube is, and the higher the output air temperature will be.

If it's cold but not freezing cold it could also be the orifice tube slowly getting clogged (it's internal, you can't check it without evacuating the system)...but something easy to try is make sure your condenser is clean and the fins haven't been damaged--sometimes simply a clogged or dirty condenser makes the system inefficient. I clean mine (house and autos) every spring. I spray on a soapy water mix from a bug sprayer, then clean it by spraying it with a garden hose from the engine out towards the bumper--if you spray from the front, you'll just drive the dirt and crap deeper inside.

 

Thanks for the info. I will first check the pressures. I have a good gauge set and I have done AC work on other cars just not on the excursion yet. I read some of the people who swear to only fill the system by weight, not by pressures.
I will see what the pressures are at and try topping it off.
Good thing the price of refrigerant has dropped.

 

what is a red herring

 

a clue or piece of information that is,
or is intended to be,
misleading or distracting.

"the book is fast-paced, exciting, and full of red herrings"