I need some guidance on troubleshooting my Dec. 1986 coupe with C68 Electronic A/C, with R-12, and the Z6A option rear defogger. The compressor does not run, but the interior control seems to operate properly (ie, the led's & fan). The previous owner said since his purchase in 1988 nothing has been done to the A/C system. My first thought was that it may have leaked down after many years of non use, and connecting the R-12 gages might tell the story. But after reading many posts & seeing all the possible variations of these systems, I thought maybe looking at trouble codes might be a better approach. I have plenty of R-12, or I might consider the Eckler 134a A/C compressor/dryer retrofit kit. Please advise on trouble codes or expected hi/lo gage readings. Thanks in advance!

 

If all else appears to be working, it could be the pressure cycling switch. In my experience, they fail with time. I have owned many old cars and if the ac compressor clutch does not pull in, this is my first test. Not a real diagnostic, just a quick check of the switch.

Unplug the connector to the switch. Crank your car, turn on the A/C. Place a jumper across the connector terminals. If the compress clutch pulls in, you have a bad switch or low freon pressure (could also be high, but most likely low). Everything else is probably working. If you have freon gauges, connect to monitor pressure on the low side. If low side pressure is 1.7 kg/cm2 to 3.8 kg/cm2 (25 to 55 psi), the pressure switch is bad.

You can do the jumper test in about 10 minutes.

 

Thank you for your prompt response. I'll follow your suggestions right after lunch, and let you know the results.

 

There are few trouble codes to help you diagnose this Year and one for no gas doesn't exist until '90. If you have gages, better to start by verifying there's gas in it because the gas carries the oil that lubes the compressor and if there isn't any, you can blow it up. Pressure, engine off, should be equal on the high and low and match the ambient shown in an R12 Pressure/Temp Chart and even a 1/2 lb of gas - which isn't enough to keep it running - should match the chart. If it's zero, you'll need to have it leak checked, pull a vacuum after it's fixed, and re-charge. Note - there's no need to replace the compressor for a retrofit, which I wouldn't do anyway if you have R12.

 

I have an '86 too that I'm going through a similar issue. My car has not been touched and has 4400 miles. I've decided to get it out of storage and drive it some, and of course, the AC was dead. The compressor would not kick in at all.
I suspected the R12 had leaked out due to non-use, and had it looked at by an AC shop last week. Sure enough, the only issue they found was serious leaks at the front seal and also the seals at the rear of the compressor where the lines attach. I'm trying to find a place that will reseal my original compressor, as I don't want to change it.

 

Good clarification. The jumper test is to see if the compressor will kick in. Until you know it has gas and oil, don't let the compressor run with the jumper. Just check to see if it will run and take off the jumper.

 

The early ODB1 ECM will ONLY code for engine/smog related problems.
This does not include ABS, transmission or accessories like A/C.








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Thanks, for adding information. So far I have checked the continuity on the following switched. The compressor engine cool temp, & the compressor pressure cycling switches both read continuity. The low pressure cycling cut off switch reads infinity. I attempted to connect my (new never been used) R-12 gauges, the fittings for the connection on the accumulator fit, but fitting to the line from the condenser are too large (there must be an adapter missing from the gauge kit) However, there is pressure at each of the valve fittings. I'll send this along, for your analysis, while I try to get a pressure reading.

 

OK approx. 16lb at 75F.

 

Bypassed low pressure cycling cut off switch and compressor clutch engages. Low on R-12, for sure. The fact that the system still had some R-12 tells me that it doesn't have a massive leak (prior to last summer the vehicle hadn't been used in 15 years) So should I just add R-12 or is there a stop leak product or other recommended procedure, that I should consider? What about compressor oil? none appears to be leaking & if it were the system would probably be totally empty & would need to be vacuumed.
Thanks!

 

R12 at 75 degrees has a pressure of 76 psi. 16 psi is a trace amount of gas or air if the leak is on the Suction Side and you obtained the reading after it was run.

If you have gas to spare, you can try to find the leak by attempting to put a can in it, but it will be difficult with essentially nothing to get the compressor to suck in a can. If you have a vacuum pump, you may be able to get it below atmosphere so that some suction occurs. Bad seals and ruptured hoses usually show up rather quickly once there's some gas in it.

 

The reading was obtained B4 I shorted the cycling cut off switch. Most likely the compressor had not turned on for more than 15 years. I have 10 cans of R-12 & years ago was EPA certified, but never had much A/C practice. Since then CRS has set in !! I don't have a vacuum pump, but could I momentarily bypass the cycling switch to energize the clutch, with the can punctured letting R-12 into the low side? I just ordered the 1/4" to 3/16" high side adapter for my gauges so I can check the system later on. Would the fact that it had 16 psi in the system B4 I energized the clutch indicate a small gradual leak such as the compressor seal?

 

Leak could be anywhere and anything, but with some pressure it usually isn't catastrophic; ie, a ruptured hose or a big rock through the Condensor. I really wouldn't know. You can try to add gas (a couple of cans) and then go to a shop for a leak test (should be free if not inexpensive as they want the big bucks to fix it). If you're going to fix it yourself, you will need a vacuum pump. The cheapos at Harbor Freight are usually good enough.

 

I was looking at vac. pumps at Harbor Freight this AM. But I'm also looking at the TPS VP125 3CFM vac pump $60+ship or the no name single stage rotary $47+ship on Amazon, similar specs to the HF @ a lower price. (even with HF coupons) If you have the time I'd like your opinion. Thanks again! I'll keep you posted.

 

R12 is going to leak from air conditioning systems according to my service manuals, will not stay fully charged forever. I have added cans to my 1970 since it was bought in 1970 new.
My 1985 still has R12 and I have added R12 to it. According to the 1985's service manual you test the charge by feel. Don't have my service manual with me, would need it to tell you where you place your hands to feel how cool the air conditioning pipes are to identify if it needs R12. My 1985's compressor has always worked pumping R12, never let it get low enough for the pressure switch not to let the compressor run.
You may be able to add a can of R12 to the system without the compressor running. If it takes the can of R12 because of the pressure of the R12 to inject it into your system, now start the car and see if the compressor will run. If it does not leave the air conditioning on and hook up another can of R12 and inject it into the system.
Last year I replaced a compressor, accumulator, and orifice tube in another car. I vacuumed the system with the "loan a tool" from Auto Zone. It was a brand new vacuum pump and no cost to use, only deposit to take it out of the store.
I added a can or two of refridgerant first and then started the car and added more, still cooling.
My 1985's GM service manual does not have information on using gauges to check the R12, just the hand feel method.

 

Thanks for your input. This morning (short story) I put in a 12oz can of R-12 and the air coming out of the duct got down to 50*, with ambient temp. at 72*. It took a while to get the whole can in. With A/C on lowest setting & fan on highest with engine at fast idle. I connected a switch across the connections that go to the cycling switch so I could toggle the compressor on & off. After approximately half a can was in, I connected the wiring back onto the cycling switch. at this point there was enough pressure in the system to actuate the switch and turn the compressor on. It then cycled on & off quickly for a while, then stabilized with less frequent cycling. My low side reads 85 psi with engine off, ambient 72*. When I get my high side adapter (later this week) I should be able to do a more thorough check. Thanks to all who contributed! Now on to the Bose cassette deck that spits out tapes, I know! I know! I'm in the wrong century! But I'm trying to get an NCRS Top Flight certification.

 

First of all, there's no "hand" test other than verifying that the Evaporator Inlet is warmer then the Outlet which should be colder, though I'd watch touching the inlet because if you feel it before the orifice you can burn your hand. Manuals assume you have gages and the Performance Charts will give the expected High and Low Side for given Ambients and Relative Humidity along with with a Center Vent Temp. As to a vacuum pump, the key is letting it run long enough to fully evacuate the System. For a one stage unit, that's probably a couple of hours and then letting it sit for another hour at which point, you generally see a reduction in vacuum as the remaining moisture boils off. You'll then run the pump another hour until everything remains steady (after you turn it off). Of course the Factory didn't do any of this running a pump and dump operation in a couple of minutes; ie, they don't shut down the Line to make sure it's the best it can be.

 

70ZZ3 96LT4, may have been referring to the "Insufficient Cooling Check Procedure, aka. "Hand Feel" Procedure page1B-6 in the 86 FSM. After posting this AM I took the car for a ride 80* temp, plenty of cold air. So at this point I won't be evacuating the system & recharging it unless the leakage proves to be more than a can of R-12 every few years, or other A/C problems arise.
If my math is correct. Figuring 2.75 LB is a full charge (3.67 12 oz cans) I added 12oz's (which may be a slight over charge base on the previously mentioned pressure temp relationship) The system had ~ 80% of a full charge, B4 I started. The cycling switch must shut down the compressor when the system leaks down to ~ 90% of a full charge??? But I'll re check with gauges when I get my adapter and adjust the charge accordingly. Thank to all contributors!