So I ground both that switch. Take one wire and put it in the two slots?

I am sorry for being a beginner on the A/C stuff. I have never had a prob with this cars ac since it was new

 

There are two separate things to try here and both involve the low pressure switch.

1 - Remove the connector with the 2 wires off the low pressure switch. With the engine running and A/C turned on, connect the 2 wires in the connector together using another piece of wire. Check and see if the compressor starts. If nothing happens, then remove the jumper wire.

 

You don't have to have the engine running to do these tests. The compressor will engage just fine with the engine stopped (you do need the ignition on, though). It's a lot easier to do with the engine off because you can hear the clutch engaging and disengaging.

I'm suspicious of the no voltage at the compressor. The voltage comes from the battery through a fusible link and then goes through the module mounted in the A/C fan shroud. From there it goes to the green wire on the compressor. You should have 12V on the green wire when the ignition and A/C are on.

 

I know your knowledgeable but you are incorrect on this. That may be the case on an 86 as you have one. But the 94 is a completely different technology and doesn't work that way. (Although that would be nice for troubleshooting if it did work that way).

I can tell you for 110% sure that the engine has to be running to engage the clutch. You can get other functions with just the key on like fan operation and blend door operation, but not the A/C clutch.

Voltage for the clutch starts out a fuse # 18 (10 A) and then goes to A/C relay via the clutch. But to turn the relay (solenoid) on is a function of the A/C control panel, A/C programmer and PCM. A fairly complicated process to turn on the A/C relay. And to get to some of the pieces is quite an effort. If any codes are set in the controller it can also inhibit the relay from closing plus monitoring the pressures by the PCM. A lot of operations and logic has to happen to make the A/C relay close.

DEREKGUZZ - It may not be a bad idea the take a battery cable off for 30 seconds or so just to re-set everything. You're never know when you might get lucky.

***My 79 Blazer does work as the 86. If I turn on the A/C with no engine, the clutch is engaged. Isn't life grand.

 

Whoa - quit letting gas out and refer to the pressure/temp chart for R134 in your Manual. R134 at 100 psi is 88 degrees and that isn't unusual, especially if there's some engine heat. That's also enough for the compressor to start. Do you have a Scanner? Really nice to know what the PCM is seeing which should be a "Yes" for a/c and a pressure sensor signal of around 1 volt if static pressure is 100 psi.

 

I went out today and checked all the fuses again, pulled the wires off the battery then tried the A/C....Nothing....I then tried to jump the low pressure switch and the compressor did not engage. Whats next? lol

 

*** FORGET step 2 in my post 22 (does not get desired results).

Did you check all the connectors including the relay on the wheel right side well.

Do you have an ohm meter and DVM?
I have more but running out of simple stuff.


Didn't think you were going to arrive.

Check the posts to see we are. Any basic suggestions would be appreciated. Probably no FSM, scanner or standard gauges.
Keep it simple as per post 21.

 

Yes I have an OHM meter. I don't know how to use it, like what setting to put it at. I will do whatever steps I need to to check this thing out. I have checked all connections. I havent checked the relay on the right side fender wall ( near the whiper fluid refill cap) as I wouldn't know what to do to check it.

 

Given the static pressure, it's a little difficult without knowing what the PCM is seeing since it drives (grounds) the Relay. To do that, a data signal travels from the Controls to the Programmer which relays the request to the PCM. Ground side is driven through the Low Pressure Switch so it has to be closed. Since it's a '94 and there are no Codes, I'd guess that the Low Pressure Switch is the culprit - either the harness (usually it's a bad connector) or the switch is open. OP might try wriggling around the Connector or holding it firmly onto the Switch (which has worked for me on some of these mid '90's GM's that have had this problem). He also needs to verify that Switch contacts are closed with his DVM (and they should be with a static of 100 PSI).

 

how to I verify the switch contacts are closed? Whats a DVM?

 

A DVM is a digital volt meter. Which usually has both ohm measurement and volt measurement in the same meter depending on selection. You probably have one.

To check the low pressure switch, you would put the meter on ohms and set to a low scale. Then with the connector off the switch, you would measure the actual switch terminals (not the one with the wires on it). It should read near 0 or a few ohms.

 

10-4...I will chime back in, in a little bit.

And reading the switch, the car should be running with the ac on correct?

 

Not correct. Nothing has to be on to check the switch. Just remove the connector off the switch and you will see the 2 pins of the switch sticking out (hard to see from the rear view).

*************************************
This procedure is to determine if the problem is from the A/C programmer and back to the control panel, or forward to the PCM and its inputs.

This procedure is done with the key turned to ON, the A/C selected ON, but the engine does not have to be running.

1 - Remove the connector from the cycling switch. There are two wires a green and a black. Measure with a meter on DC volts the black wire in the connector. The other lead from the meter goes to ground on the engine. The measurement should be between 10 and 13 volts.

2 - Then connect the two terminals in the connector with a piece of wire. Measure one end of the jumper wire with the positive lead from the meter. The measurement should be 5 - 6 volts DC.

3 - At this point if the voltages are good in steps 2 and 3, the engine can be started. While still monitoring the same point the voltage should be about 6 volts for normal operation which the clutch should be engaged at this point.

 

tomorrow am I will do the tests and chime back in

 

RESULTS:

Step 1: 11.2 volts

Step 2: 5.51 volts

Step 3: 5.50 volts

No clutch engaging at this point.

 

That's good, that means the control panel, A/C programer and input into the PCM all are good. But for some reason the PCM is not turning on the A/C relay or something in that circuit being the solonoid or relay contacts are not doing the right thing.


Make sure the high pressure sensor (the lower unit with the 3 wires on it) connector is seated properly and there are no wires ripped out.

The signal for the Relay comes from the PCM. Did you have it disconnected? The black (labled) connector is where the output is for the relay. You can start the car, put the A/C on and push or wiggle the connector (its on top) and see if the compressor starts.

Need a new plan, will be back.

 

""The signal for the Relay comes from the PCM. Did you have it disconnected? The black (labled) connector is where the output is for the relay. You can start the car, put the A/C on and push or wiggle the connector (its on top) and see if the compressor starts.""

Confused about what and where you are talking about. I will get the car running and wiggle every connection connected to the system. I have not tried wiggling anything yet.

 

I don't see where you checked continuity across the Low Pressure Switch Terminals. The harness has the voltage, so if the switch is closed, the Relay should turn on the Compressor and if it doesn't the Relay is shot. Get a new one and it's fixed.

 

The PCM is the unit on a bracket above the battery with 4 plugs going to it. Don't disconnect them, just give it a push inward.

The A/C relay definitely can be bad. You can go and buy one or do this procedure which might tell us if it is bad or something else is wrong. It's a bit more involved than the other one you did. To do this procedure the low pressure cycling switch must be connected and closed. If you have not done this, it needs to be verified first. Or you can simply jump out the connector as you did before for the other tests. If the cycling switch is not closed, then this procedure will not be valid.

1 - Remove the relay from the inner wall of the right side fender. The relay is under the surge tank on a bracket. It's held on by two 7 mm screws on the outer wall of the fender. Remove screws and pull the relay up so you can see it.

2 - There are 2 brown wires, green and a green/white wire. Get 3 straight pins (like for sewing) and you are going to insert them in the bottom of the connector. Slide the pin down along side of the wire till it seems to stop or hit the metal terminal inside. About a third of the pin should be still visible when it stops. Insert one pin into either brown wire and the two other green wires. These will be live when you turn the key so don’t short them out to ground.

3 - connect you meter to ground on the engine and set to DC volts. Turn the key to ON (engine off). Measure the 3 pins one at a time with the lead of the meter. The measurements should be:
Brown - 11 - 12 volts
Green - 0 volts
Green/ white - 11 - 12 volts

4 - Now make sure relay is secure and won't fall and start the engine. Make the three same measurements as you just did. The measurements should be:
Brown - 11 - 14 volts
Green - 11 - 14 volts
Green/ white - 0.2 volts (anything less than 0.5volts is OK).

This will tell us if the relay is being turned on and if it has proper voltage to it.

 

I will try the new procedure tomorrow AM...This is kind of fun. I hope I am not making anyone mad about the time ti takes to help me out. I am used to throwing parts at stuff. But finding the problem is fun too. Stay tuned