Another noobie question, I have a recently bought 79 and of course the a/c will not work.

I jumped the compressor and the clutch ingaged. so i thought maybe the low pressure switch was bad, looked every where for it but couldn't find it, found a connector with 2 wires by the accumulator that was not hooked to anything. started reading here about two hours ago and found a thread that said mine did not have a low pressure switch and another one that said they had hooked one up and their system worked. so can some one tell me if the 79's had one and if they didn't how or where should i look to find how the pressure was controlled?

Thanks, Joe

Another noobie question, I have a recently bought 79 and of course the a/c will not work.

I jumped the compressor and the clutch ingaged. so i thought maybe the low pressure switch was bad, looked every where for it but couldn't find it, found a connector with 2 wires by the accumulator that was not hooked to anything. started reading here about two hours ago and found a thread that said mine did not have a low pressure switch and another one that said they had hooked one up and their system worked. so can some one tell me if the 79's had one and if they didn't how or where should i look to find how the pressure was controlled?

Thanks, Joe

What does your connector look like? If it's round with 2 terminals it's for the low pressure switch. If it's 2 separate terminals, it's set up for a thermostat. Either way, you can screw a switch onto the accumulator fitting and connect the wires to it.

Don't be surprised if the compressor still doesn't engage. It sounds like the system hasn't worked in a good while, so there's probably little or no refrigerant in it.

79 Should have a thermostatic switch.

The connector is rectangular with three slots for wires,but only has two wires, one light green and one dark green.
where would the thermostatic swich be located?

Anybody ????

It plugs into that connector. It is a replaceable part at any parts house. It is about the size of half of your little finger.

are we talking about a thermal limiter?? or something else??
i never did figure out what they do??:dontknow:

http://www.uacparts.com/catalog/homepage/Search/SW/images/280/SW%205759.jpg




a low press. or cycle switch,, screws on to the accumulator..:texas:
http://www.uacparts.com/catalog/homepage/Search/SW/images/280/SW%201122C.jpg

Now i'm not sure, the connector by the accumulator with two green wires has a socket that would hold three wires, but only has two looks like it would hook to the thermal limiter, it has three slots but only two wires.

No other connectors near by look like they would hook to the low pressure switch.

My el is a 79 according to the vin. and i don't know for sure if gm changed in mid year or something, but what i've been told the 79s had a thermal limiter and had something that was wrapped around the evaporator tube that measured temp and if it got to hot it would cycle the compressor. However the accumulator has two scrader valves on it.

I'm confused
Thanks for any input.

UP Date !!!!!!!

This car has an A6 compressor, i know where the connector for the clutch is, but on the rear
of the compressor there is a wire it looks to be green also and it has a connector about 10" from
the compressor and its mostley melted. any ideal where it goes?

If the connector looks like a thermal limiter switch connector then the melted wire you have probably went to a superheat switch on the back of the compressor. Someone may have tried to bypass the circuit in the past.

Try this for grins. The two wires should be a light green and a dark green. Install a jumper between the two and post results.

If the connector looks like a thermal limiter switch connector then the melted wire you have probably went to a superheat switch on the back of the compressor. Someone may have tried to bypass the circuit in the past.

Try this for grins. The two wires should be a light green and a dark green. Install a jumper between the two and post results.

Tried the jumper and nothing happened. The only way i can get the clutch to engage
is by supplying 12 volts to the compressor.

J did you have the a/c switch on? does it have power?:texas:

Yep,, Had it on max and temp full cold, fan was blowing but not real hard.

i believe that lite green wire should be hot with the a/c switch on,,
trace it back and see if you can find a problem??:texas:

OK, found the other part of the connector over by the accumulator, it also has a light green wire and dark green wire and goes thur the fire wall "i'm thinking to the thermo switch.

I also replaced all the orings and accumulator,orifice tube, vaccumed it down and it held 29"s of vaccum for over 30 min's. Then i tried to charge it the clutch would not cycle. i was in the process of running jumper wires again and when i hooked the black wire from the compressor to the neg side of the battery the clutch engaged????????

Then i thought i would ground the one wire coming off the back of the compressor as its susposed to be the high press. switch, well it blew the fuse and the blower motor quit, replaced the 25 amp fuse, grounded the compressor to the neg. side of battery with a jumper wire and started charging the system. (also discovered the temp control valve for the heater is in the open position and hot water going into the heater core, will address monday) Getting cool air thur the vents !!!!!!!

Sorry, but my next question is whats the deal with having to ground the clutch to the battery neg. side in order to ingage the compressor clutch and what am i missing on the one wire coming out of the back of the compressor???

Thanks To everyone for helping, maybe there is a light at the end of this tunnel.
You guys are great!!!!!!!

wtg J
the black wire at the clutch completes the curcuit for the clutch,,its the neg. for the green pos,,
its usually grounded to the compressor bracket off the motor,,the clutch is an electro-magnet..

im not sure where the rear/hi switch goes,,ill check my book..
i dont think it needs a ground..:texas:

HELP
my books are worthless for a/c wiring..:texas:

id think the rear swith would interupt the power to the clutch:dontknow:to save the compressor:dontknow:

Thanks jj

I have a factory manual coming for a 79, I got one of the haynes and it's kinda vauge
on a couple things,wiring is one of them, hope the factory one will help.

Will post when i find out.

That green connector by the top of the fender well is to hook up diagnostic equipment. On my 87 thats what it's for.? I think theres a blue plug also for the same reason. This is on the passenger side by the accumulator.

My 78 has an A6 compressor and uses a thermostat at the evaporator to cycle the clutch.
The thermostat looks like this: http://rover.ebay.com/ar/1/711-53200-19255-0/1?mpt=758431056&adtype=1&size=1x1&type=3&campid=5336121877&toolid=10001 http://compare.ebay.com/like/180406117734?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y (http://rover.ebay.com/rover/1/711-53200-19255-0/1?type=3&campid=5336121877&toolid=10001&mpre=http%3A%2F%2Fcompare.ebay.com%2Flike%2F180406 117734%3Fvar%3Dlv%26ltyp%3DAllFixedPriceItemTypes% 26var%3Dsbar%26_lwgsi%3Dy) Most of the sensing tube is hidden from view in the evap housing.

The black wire on my clutch connector is grounded to the compressor mount.
On most thermostat controlled systems, the black wire would go to the superheat switch so that it would open and disable the compressor if the refrigerant charge got low. (I believe that is how mine "should" be, but I have no switch on the compressor).

On older A6 equipped systems, the superheat switch was normally open. When it closed, it would blow the thermal limiter. That was on pre-1978 POA and VIR systems.

Hope this helps.

LSRX101,,,,
How did you bypass that switch on the compressor?

i've installed the thermo switch, the system is still holding a charge and if i ground the clutch it cools good(another problem) on the trans tunnel 42 degrees.

The wire on the back of the comp. is a one pin connector,the replacement has two wires and instructions say one wire to the pin and the other to the harness or ground:???:. Before i go thur having the system evacuated to install that switch was wondering what you did.

Thanks

My compressor circuit was modified when I bought the car.
The black wire from the clutch coil is grounded to the comp. mounting bracket. There's no switch on the rear of my compressor.