kevinruswick

Thanks for the advice. Gave it another go tonight, first pulling a good vacuum on the system for about 30 minutes. Then added some refrigerant and UV dye as I wanted to check for any remaining leaks in the system. After about 6oz of refrigerant, the coolant fan came on and system pressures were around 40 psig, however compressor still didn't come on. I did try jumping a wire from the compressor to the battery and it did engage. Pressures were fluctuating, high side going towards 150 psig and low side dropping towards 25 psig. Didn't see much with the UV dye and light, so I don't think there are any major leaks remaining. My bigger concern is that there is an electrical or hopefully just a sensor issue. I still don't quite understand why the auxilliary coolant fan will come on after charging the system, yet the compressor won't turn on. I also tried re-starting the car after about 30 minutes and turned the Econ setting on. Auxilliary coolant fan still came on which was a little surprising. I thought it was only supposed to come on when the AC system/compressor was on. I am decent mechanically, but electrical systems were never my strong suit. I've looked at the Bentley wiring diagrams but couldn't find anything that actually showed the AC compressor wiring. I am obviously frustrated at this point but also very stubborn and want to fix this problem without having to take it to the stealer or an indie mechanic. Could a faulty pressure switch allow the coolant fan to turn on but not turn on the compressor? Thanks in advance for any suggestions.

SloopJohnB@mac.com

BUT you still haven't checked the output/continuity at the LP switch?
Since you jumped the LP switch and the compressor came on and pressures dropped LS and HS, I would replaced the LP switch (unless there is NOT 12V on one side of the LP switch...i.e., you have to have supply as well).

Check the bentley wiring diagram for how 12V gets to the LP switch if you don't have 12V at one side of it.

kevinruswick

Thanks again. I plan on testing the switch tonight with a multi-meter. My understanding is that the switch controls both the electric cooling fan and the compressor. The fan comes on but compressor does not. Also fan doesn't turn off when the Econ mode is set at the climate control panel. The pressure switch certainly seems like a logical culprit. Hopefully my further testing will confirm. It's only about a $50 part and looks easy to replace.

kevinruswick

Got out the multi-meter, my Bentley manual with the electrical wiring diagrams and did some testes on the AC pressure switch. Tests were at the red 4 pin connector in the left engine compartment under the removeable plastic cover by the power steering reservoir. First did continuity tests without the car running to test the static condition of switch. Multi-meter showed no resistance (closed switch) for the coolant fan circuit and infinite resistance (open switch)to the AC control head, which I assume controls the compressor. The Bentley wiring diagram shows the switches with opposite settings; i.e. it shows the coolant fan circuit default at open and the AC control head circuit default at closed.

I then did a voltage test for the power supply to the switch with the car running and AC on (Econ setting off). Got about 13.5volts feeding the switch. Also jumped the wires in the connector controlling the AC control head and compressor kicked on. So, I think this confirms that there isn't a fuse or relay issue with the AC system.

I think this all confirms that the AC pressure switch is the problem. The one piece of the puzzle I am still trying to come to grips with is that the coolant fan didn't come on until I charged the system. This leads me to believe that the newly pressurized system did activate the pressure switch to close the coolant fan circuit but now it must be stuck in the closed position since the coolant fan runs even when the AC is off (Econ setting ON). Don't know if that is a sign that the coolant fan control module is bad or if it is still an AC pressure switch issue.

Anyways, I did order a new AC pressure switch that should arrive tomorrow. Got it from PelicanParts.com for $42 plus shipping. Dealer wanted over $200 for the part! Hopefully it will be an easy install and fix the problem. Has anybody replaced this switch and have any advice?

jschick

also confirm your wiring is good to your compressor. I just found mine must have rubbed on the clutch and wore thru the wire. it looked just fine but when I pulled it I realized it wasn't hooked to the compressor!! I am going to replace my clutch this weekend.

kevinruswick

Bad news, replaced the AC pressure switch and still no luck with the compressor kicking on. Same situation as before, coolant fan turns on but no compressor. I did hook up the manifold gages and it shows static pressure of about 30 psi. From what I've read, that should be a reasonable pressure in the system. But checked the continuity for the AC control head coming off the pressure switch and it still showed an open switch and the coolant fan showed continuity. Also checked power again to the switch red pin connector; showed 14 volts without econ setting on and no power with econ setting on. So, I think it is still fine on the power, relay side. Still can't figure out what the problem is with the pressure switch side of the system. For some reason I feel like the wiring with the switch is flip-flopped; i.e the coolant fan is showing static continuity instead of the AC. When I first charged the system, when it hit about 15-20 psi, the coolant fan kicked on, but not the compressor.

Other thought is that something is wrong with the pressure in the system, maybe a blockage or something. When I did jumper to kick the compressor on, low pressure side fluctuated between about 25-35 psi and high side fluctuated between about 50-80 psi. Wouldn't stabilize even after running for about 10 minutes. Other item to note is that system only took about 10 oz of refrigerant to get to the 30 psi static pressure. Specs show system should take up to 28 oz of refrigerant. I am not experienced in AC systems but do have a technical engineering background.

Anyways, I think I am at the end of my line with this car. It gets crappy gas mileage, likely has a clogged egr port, has 131k miles. I've put a lot of money and effort into this car to get it running and fix the incorrectly repaired front end damage, but this AC problem is too frustrating. Any last thoughts before I abandon this project?

kevinruswick

Well being a stuborn one, I took another look at the AC compressor issue. As noted in last post I suspected there may be a wiring issue as the pressure switch continuity seemed flip flopped between the coolant fan and the compressor. Guess what, I found the connector wire had been spliced! And the stupid idiots who did it couldn't even match the colors of the wires. Maybe they were color blind... So, I finally got the compressor working correctly and was able to add additional refrigerant until I was getting about 30 psi low side and around 200 psi high side. Air was blowing nice and cold inside as well. Compressor turned off when econ button was on, so I think mechanically and electrically I got things in order. Only setback now was that I found a couple of minor leaks at the hose connections near the passenger side of the condensor. Going to need to pull the front bumper to get to those lines and didn't have time today. Just happy to know I wasn't a complete idiot with my testing and diagnostics; logic doesn't make any sense when fricking wires are spliced incorrectly!

SloopJohnB@mac.com

Sounds like a failed orifice or expansion valve or inadequate refrigerant. High pressure side should be pushing 200-300 psi on R134A if you have 25-35 on the LP side and adequate refrigerant flow. A plugged orifice would give you really high pressure on the high side and relatively higher pressures on the low side (than 25-35).

I remember I had a volvo that the AC worked fine but after 12 years of no problems I decided to replace that filter and the receiver/dryer and recharge the system (sorry BB, it wasn't broke but I improved it). The filter was about 60% clogged (it had five sections and 3 of them were discolored, clogged. Volvo service manual noted this was how you could tell the filter was clogged/clogging). New filter and sucked/charged and the AC system was working like new...pulled about 39F IIRC, of course on R12. Last car I owned on R12...sigh.

Here's one way to go at it:
http://www.aa1car.com/library/ac98.htm

VipDesigns

I am having the same issues with my A4(B6) 1.8T. Did you give up, or did you find the root cause of the problem.

audi1031

I would try your fan control module replacement. Dooes the aux fan come on when A/C turned on?