kevinruswick

I've got a 2000 A6 Avant quattro with the 2.8l ATQ engine. I've been trying to repair after some front end damage. Latest thing I've noticed now that it is getting warmer here in upstate NY is that the AC compressor is not kicking on. Tried cycling the Econ button, but nothing. I'd like to at least troubleshoot a little on my own before bringing into the shop. From what I've researched, could be a multitude of problems from fuse, relay, hi/low pressure switches, compressor clutch, or the compressor itself. A lot of the info I've read notes the need for AC manifold gauges to measure the hi and low pressures. Since the compressor won't turn on, is it still a good first step to measure the hi/low pressures or are there more logical electrical tests to conduct. Thanks in advance for the help.

4Driver4

Most common issue is no refrigerant in the system...especially given the front end crash. Start by have a shop check the charge.

SloopJohnB@mac.com

Short answer is yes...good to check static pressures. If below 20? the compressor won't turn on. And if it does, chances are the suction side will drop way low enough to trigger the low pressure switch.

You don't need a shop to check the charge...any cheapo Freeze134plus or whatever such as

http://www.amazon.com/Interdynamics-...xp_grid_pt_1_2


will work. LOL...my 2K4.2A6 gets recharged with a can every spring. Has been ok for 3 years now...got tired of taking it to the stealer who sucked and charged and tested and pronounced it ok only to have to do it again in a year.

kevinruswick

Thanks for the reply. I did run a quick test to make sure the AC compressor and clutch were functional. Based on some other advice, I unhooked the single wire connector in the cluster near the power steering reservoir. Did a quick jump front the connector to the Positive terminal on the battery. Got the click I was hoping for. Also tried it with the engine running, heard click and saw the clutch engage, turning the compressor. So, good news that the compressor and clutch are OK. Guess the problem is most likely low refrigerant. I am debating trying the quick refill strategy now. Must have been or is still a leak in the system. My thought was to get an AC manifold gauge set from harbor freight as well as a air vacuum pump. My understanding is that it is really important to purge the system of air and moisture and the vacuum test should show it able to hold a vacuum of 27-30 Hg before adding more refrigerant. Does this sound reasonable or should I just try the quick refill to see if it may get the system working. I don't have long-term plans with the car, really just hoping to get another year out of it and would like the AC working at least through the summer. So, obviously looking for the cheapest alternative at this point.

SloopJohnB@mac.com

LOL. Your cheapest alternative IS the quick refill. Like I said before, just fill is with ArcticFreeze134A+ or similar..you don't even need to get the refrigerant gauges/manifold from Harbor Freight unless you want to check the high pressure side. I just fill up the low pressure side to where it holds 30psi on suction and it works fine.

Depending on how much of your lubricant has also leaked you may have to put some more oil in..highly recommended after adding 3-4 cans of refrigerant over a couple years.

http://www.amazon.com/FJC-Estercool-.../dp/B003T0VRQO

Of course, the only way to be sure you have the correct refrigerant/lubricant charge is to purge/drain the system and reload from zero (technically way less than zero since the system is sucked down to a moderate vacuum).
YMMV.

4Driver4

Why do a quick refill if you don't have the equipment to locate the leak?
An AC is not a lot of money.

kevinruswick

Just an update on the AC issue and unfortunately another call for help. I did purchase an AC manifold gage set and a vacuum pump. System was empty of refrigerant, but when I hooked up the vacuum pump could only pull about 10 hg. Figured there must be a leak and I found it on one of the lines coming from the condenser. I ended up taking the bumper off and getting the line tightened correctly and the system held 30hg of vacuum for several hours. FIY also replaced the accumulator/dryer. Anyways, thought a simple charge with refrigerant at this point would bring the system back on line. Started charging with first can (no sealer), low side pressure went up to about 35-50 psi and auxilary coolant fan kicked on. So, I thought everything was working alright, but when I opened the high side gage, it read the same pressure as the low side. Basically, the compressor isn't kicking in. Previous to all of this I had jumped a wire from the compressor to the battery and it kicked on, so trying to figure out my next step. Interesting that auxilary coolant fan kicked on but the compressor didn't.. Anyways, just trying to figure out my next step. Relay, pressure switch? Any help would be greatly appreciated.

jcman

Pag/POE oil is a sponge for moisture and moisture in a 134-A system is sudden death because if the drier or desicant is already hydro-saturated causing resrictions before the metering devise when high pressure meets low at the evaporator wil cause your LP switch to open. Pulling a deep vac with this oil may not be the trick, my advise would be to replace your drier or release the moisture by sub-heating the drier with a hair-dryer while pulling a vac to at least 100 microns with a micron meter, there is no perfect 30 on earth and I will not get into the reasons why because it's done in space with true RMS results. Man is miss R12 and mineral oil.

kevinruswick

Thanks for the reply. I did replace the drier prior to leak testing and recharging the system. Also had used a vacuum pump before recharging. Would moisture still be an issue with the new drier? Could it be a bad pressure switch?

SloopJohnB@mac.com

You can check the output from the low pressure switch. If you have 30psig in the static system the LP switch should show continuity or 12V to the compressor clutch.

If you have 30psig static you can also bypass the LP switch (you already did it once...do it again) and monitor the pressures. High side should go over 250psig and low side shouldn't drop below 25 or so. If low side drops below 20 add more refrigerant (as long as high side is up).

Yes, it's best to suck them dry/hold vacuum, then add the proper oil and refrigerant charge quantity.