JUST HAD THE DASH OF MY 84 APART ,HAD THE RADIO AND HVAC CONTROL OUT. NOW,THE A/C COMP. DOESNT come on. I HAVE RECHECKED ALL WIRE CONNECTIONS,ALL OK THE BLOWER WORKS,THE VENT SWITCHES OVER,ALL WORKS AS NORMAL. I.V CHECKED THE FUSE,JUMPED THE PRESSURE SWITCH,IF FREON LOW. MY QUESTION TO YOU PROS IS. THE OUTSIDE AMBIENT TEMP WAS AROUND 50 DEGREES. IS THERE A TEMP.SENSOR,THAT WOULD KEEP AC COMP. FROM comeing on WHEN ITS THAT COLD. WHAT CYCLES THE AC UNDER NORMAL SUMMER USE. DON'T WANT TO SPEND TIME TRYING TO FIX SOMETHING THATS NOT BROKE. THANKS PROS BY THE WAY JUST A DUMB ? WHAT DOES ROFL STAND FOR I DON'T TEXT LOL

 

I don't know what you mean by cycling which usually means the compressor is continually turning on/off.

A low pressure switch - which I guess you jumpered - needs 50 psi to close the contacts and that completes the clutch circuit. With that, the compressor engages and will remain engaged until the Low side drops to 25 psi (26 degrees, though it's actually about 33 to 34 degrees with superheat). The contacts then open and the the compressor turns off and this keeps the Evaporator from becoming a big ice cube. With the compressor no longer running, the pressure rises and the process repeats.

Pressure is a function of charge and ambient air temp. At 50 degrees, R12 is 53 psi. At 40 degrees, it's 43 psi. If it's a tad low, or if your thermometer is inaccurate, it won't have enough oomph to get the contacts closed until some engine heat warms it up. You'll probably need to close the hood if it's much below 50.

At these lower ambients, the compressor will be off more than it's on. Specs for any system is 8 cycles or less per minute at 70 degrees (though at 70, a fully charged system shouldn't cycle; ie, it should stay on). Rapid cycling is an indicator that the charge is low or that the metering device is plugged up.

Without a manifold gage set to show you the pressures, difficult to know if there's any problem, but if it worked before you took the dash apart, it should at least have the same amount of gas in it that it started with. You could, if you don't have a gage set, put a digital thermometer on one of the lines and whatever temperature you get, get an idea as to what the pressure is. Otherwise, go drive the crap out of it or disconnect the Main Fan and let the engine temp get up to 220 or so, and see what it does.

 

thanks suncr thats alot of info. your correct i should not have used the term cycling(i have changed that in the orig. post to say coming on. the clutch does not activate at all. volt meter on the comp. clutch shows no power. correct me but if the freon was a little low, would not jumping the low pressure switch bring on the comp. in case of more then 1 problem,like clutch bad,also, i kept the volt meter on the comp. clutch when jumping low pressure sw.. still no power . i know its hard to trouble shoot via. a forum, thankyou very much for your attempt. i'm in las vegas now and the cars in utah,it was 21 degrees that nite and reached a high of 50 that day when i was working on it. i'll be back up there in a couple days and start checking it out again. again thanks tim

 

Jumpering the Low Pressure Switch Connector should have engaged the Compressor Clutch. Circuit is fairly simple. Fused ignition power (usually 20 to 25 amps labeled a/c) to the Control Panel. With the Controls on A/C, Defrost or Bi-Level, 12 volts runs to the Low Pressure Switch and if the Contacts are closed, out to the High Pressure Limit (on the Rear of the Compressor for an '84 which opens above 400 psi so a backed up system doesn't blow a hole in the hood) and then to the Clutch coil which is grounded to the Chassis. There's usually a splice somewhere which runs to the ECM for idle and WOT control. Start by making sure the fuse is intact and that there's 12 volts across it's terminals - maybe you shorted something when the Dash was apart? If it's good, check for 12 volts at the Low Pressure Switch Connector - should be hot on one side. If that's ok, check it at the High Pressure Connector.

A couple caveats: Power is only applied in the Run Position - Accessory and Start are disabled. Circuit may run to the High Pressure Limit first and then to the Low Pressure Switch, though it really doesn't matter. The High Pressure Limit should always be closed with the engine off or when the compressor isn't engaged. 400 psi under those circumstances is impossible (unless the engine has caught fire). Some High Pressure Limits, if they've opened for any reason, don't reclose so if yours is open, replace it. Never jumper a high pressure limit connector (or stand anywhere near the system if you do).