2000 grand marquis no A/C

[badman41]

I purchased an 00 GM, compressor clutch does not engage- no voltage at connector going to compressor. I benched checked all relays having to do with the A/C and they work (A/C cutoff relay is ok and relay that I think feeds the clutch is ok), checked all fuses- all ok. Connected a gauge at the accumulator- reads about 30lbs with car running and A/C turned, tried adding R134, wouldnt take any. What voltage should I read at the low pressure sensor (2 wire) on the accumulator- with the car not running but the ignition key on and the A/C turned on, it reads 12 vdc. With the ignition on (car off) A/C turned off, it reads 0. I read in the forum about pulling off the pressure sensor connector and jumpering the 2 pins. Can this be done safely without damaging the A/C system?

The car sat for 4 years, otherwise runs great.

[cm5400]

Was the compressor on and turning when you got the 30 psi reading on the low? If not, your system is empty unless it was 30 degrees out. Are you using actual gauges or some other contraption?

As far as jumpering the connector, I would wait until you figure out if the system is empty. You don't want the compressor running without any oil.

[mattelderca]

Well, with my small knowledge of ac systems I would say that 30 psi with no compressor running would indicate an empty, or near empty, system. This would explain why the compressor is not coming in. I'm working on a similar GM myself, a 93. A proper evac and leak test should be in order for your system. Others may have better info.

[badman41]

With 30psi, compressor was not on, it never turned on. I tried adding R134, it wouldnt take any. Why is that?

[Nacho]

Chances are you have a leak either in the discharge hose of in the compressor's shaft seal. Oily areas in the hose going from the compressor to the condenser is a telltale and quite common on these vehicles.

To make the compressor run, you can jumper the pressure cycling switch in order to dispense refrigerant.

[cm5400]

Badman41,

Follow Nacho's advice to find and fix the leak; and then follow his charging procedure at --> http://www.aircondition.com/tech/questions/95/Basic-Charging-Procedures

[badman41]

Thanks for all your advice guys. I connected a 12oz can of R134, jumpered the low pressure switch, turned on the AC and compressor immediately kicked in (wouldnt turn on before). As the system sucked in refrigerant, I removed the jumper and reconnected the connector to the low pressure switch. The compressor now began cycling off and on rapidly, less rapidly as time went by and more refrigerant entered the system. I used up one 12oz can and emptied another. The air gets cold now. I think I need one more can- the local NAPA parts store told me this car needs 2.4 lbs or 38oz

You guys were right in that the system was completely empty (car sat for 4 years). I'm hoping now there is no leak- time will tell.

[mattelderca]

You guys were right in that the system was completely empty (car sat for 4 years). I'm hoping now there is no leak- time will tell.

Of course there's a leak, how did the system empty itself in the first place?
I am new here and just learning myself so don't take me too serious!

[cm5400]

Thanks for all your advice guys. I connected a 12oz can of R134, jumpered the low pressure switch, turned on the AC and compressor immediately kicked in (wouldnt turn on before). As the system sucked in refrigerant, I removed the jumper and reconnected the connector to the low pressure switch. The compressor now began cycling off and on rapidly, less rapidly as time went by and more refrigerant entered the system. I used up one 12oz can and emptied another. The air gets cold now. I think I need one more can- the local NAPA parts store told me this car needs 2.4 lbs or 38oz

You guys were right in that the system was completely empty (car sat for 4 years). I'm hoping now there is no leak- time will tell.

I hope you pulled a deep vacuum on the system before you charged it, otherwise you are heading down the road for major problems... Weird operating pressures, erratic cooling, and acid corrosion on the internal parts leading to a possible complete system replacement, just to name a few issues... Don't mean to scare you, but you really need to get the moisture out of the system.

[Tom Greenleaf]

Just butting in

There may not be a substantial leak. Sitting for four years is an issue! I've deduced but not proven that especially when a car sits unused with no excercise to the A/C which even happens in Winter with usually a defrost request that the shaft of compressor and seal don't necessarily expand and contract at the same amounts. This has been noted for ages now on some old cars of my own - some spend a year or more in moderated temps and sometimes will see serious below zero F temps even in storage and they are low when Spring/Summer comes but not leaks ever get found and no oil evidence at that shaft seal??

Ah - Ha! Thinking about that, the oil has all settled to its lowest points such that gas alone can escape when you aren't looking of course and all is well later when either boosted up or show that it will hold a vac and work for a whole season and I put it away again for who knows how long.

Didn't read the whole thread again but if it works and lasts call it good luck. A real leak will show itself with use now.

BTW - you found it so low - did you charge into a vacuum or just fill it up? When static pressures are found lower than temp in F there is an opportunity for air to have gotten in if the compressor cycled at all when run or while running low with suction side pressure dropping into vacuum #s for a short while before compressor shuts down - leaks exposed to that would/could suck in air,

T