I am trouble shooting my a/c problem and can't seem to locate the programmer. The manual has a cryptic illustration that tells me to 'remove the instrument panel left-hand sound insulator'. While I am not sure what that is, I have the a/c head out, the radio out, all the knee panels out below the steering column and be darned if I can find the programmer. Help!

On the a/c problem, the compressor is not coming on when asked via the CCM. The head shows no codes when running the diagnostic procedure. If you hot wire the compressor it comes on and blows snow, jumping the low pressure switch doesn't turn on the compressor, I've swapped the CCM, with no change, so I am down to locating the programmer and swapping it out. Any comments would be welcome.

 

When you set the Control Head for AC operation, it sends a signal to the Heater and AC Programmer. The Heater and AC programmer sends a AC request to Pin 15 of the ECM Red connector.

The ECM then grounds the AC Clutch Relay via pin 13 Yellow ECM connector.

The High Pressure Cut out Switch, Low Pressure Cycling Switch and Clutch coil are all in series. When the Clutch Relay closes 12 volts goes through the AC High Pressure Cut out switch which should be closed, through the Low Pressure Cycling switch and then the 12 volts goes to the Clutch Coil.

You need to remove the black plastic panel under the driverside foot well that also contains the courtesy footwell lamp.

Then lay on your back and look up above the gas pedal area mounted up on the firewall is the black plastic box with some vacuum hoses going to it and one electrical connector. That's the AC programmer.

 

Hooked on Vettes:

Thanks for the input and taking the time to answer my question. The programmer has been located, thanks to your help. One correction on my earlier input is that I tested the clutch relay by jumping it with a cotter pin (not the low pressure switch), and the compressor did not start.

HOwever, I don't know how to test the high pressure cut out switch nor the pressure cycling switch.

One of the reasons I was headed to the programmer was that I believe the CCM is good, and a good friend, having been a chevy parts manager for 25 years remembers the techs being baffled often on resolving a/c problems and the programmer was the culpret. In the absence of testing the above switches, I guess I am shooting in the dark, and just playing swap 'til you solve the problem. Can you help me out with testing those switches??

I'm not 100% on reading wiring diagrams but it appears that if the CCM and the programmer are operational, then the ECM grounds the A/C clutch relay, but if the high pressure cut out switch and or the pressure cycling switch are open, then the compressor clutch isn't activated.

 

First disconnect the negative battery terminal for a couple of seconds and then reconnect.
Start the engine and see if the AC Clutch engages. If the Clutch engages you're most likely low on refrigerant.

If it still doesn't work try the below.

With the ignition in run the Fuse labeled AC applies 12 volts to the Brown wire of the AC Clutch Relay. Verify the fuse is good.

You said you got the Clutch to engage. Did you apply 12 volts direct to the Clutch Coil?

To bypass the Low Pressure Cycling switch you unplug the electrical connector and at the connector jump the two pins together.

Low Pressure Cycling switch is screwed into the larger metal tube at the evaporator housiing. The electrical connector wires are Black and a Dark Blue wire.

Same with the High Pressure Cut out switch. You unplug the connector and short the two pins at the connector together. The switch is about 1 foot from the evaporator housing screwed into the smaller metal line. The electrical connector has a Light Green and a Black wire.

Start the engine and turn on the AC. The clutch should engage.

If the Clutch engages, that tells you one of the switches is open.

With the ignition off, You can test the switches by using an ohm meter.
Should measure zero ohms across the switch which indicates the swtich is closed.

 

HOV:

On hot wiring the compressor, I ran hot and ground wires from the battery to the connectory on top of the compressor. With the CCM set to fan rate 10 and defrost, the clutch engaged and within seconds the air started getting colder and colder.

I will attempt to follow your directions and test the switches.

Thanks again,

Don

 

HOV:

I just jumped what I belive to be the low pressure cycling switch and the compressor engaged and cold air was realized. Does this mean that the switch is bad or that there is really low pressure in the system?? If I remove the switch, with this allow coolant to escape?

 

If you jumped the electrical connector for the Low Pressure Cycling switch and the clutch engaged, that would indicate either you're low on refrigerant (need at least 47 psi for the switch to close). Or the Switch is bad.

Could also be the connector just needs to be reseated.

You need to measure the pressure using a gauge. If you look at the Accumulator (Silver colored metal can) you will see the Low Pressure test port. Sometimes it has a black cap screwed /covering it. You attach a test gauge to that port. With the engine off you should measure more than 47 psi for the Clutch to engage. Someone said they used a tire gauge to test the pressure.

Since you said the air blew cold when you jumped the Clutch, the Pressure Cycling Switch could be bad. It's screwed into a schrader valve similiar to a valve core used on tires.

You can replace the Low Pressure Cycling Switch with out discharging the system. When you unscrew the Low Pressure Cycling Switch you will lose a little bit of refrigerant as long as the schrader valve is depressed. So the faster you unscrew the Switch, less refrigerant will be lost.

 

I have an 86 E with the electronic temp control. I am experiencing the inoperabilty of the system other than to select temperature, and fan speed.
It is stuck in bilevel, and I bought another programmer out of an 87, and stuck it in, and no difference.
I was talking to another forum member who had the same problem, and he sent me a wiring diagram, and a vacuum diagram, and i haven't got time to go out and fix it yet due to the 105+ temps here lately.
anway, use a vacuum pump as he suggested, and suck down each of the vvacuum motors to determine that they work, and verify that you have engine vacuum coming inside the car.

 

Just wanted to close this thread out and reply that my problem with the a/c has been resolved. The low pressure cycling switch was bad. I want to thank "Hooked on Vette's" for all the help.

Don