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George H.
George H., ASE Certified Technician
Category: Chevy
Satisfied Customers: 16048
Experience:  GM Tech ASE Master Tech 15+ years
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1998 chevy blazer: The clutch wont kick..release..vent

Resolved Question:

My A/C in my 1998 chevy blazer just stopped working. The clutch won't kick on to blow cold air. The blower works just fine and I hear pressure release from the drier when i kick it to the vent setting. I just purchased a new compressor and it came with a new drier. do you think it is the clutch that went out or the control panel inside the truck? I know every vehicle has it's quirks. Could you please give me a diagnosis of what it more than likely is.
Submitted: 4 years ago.
Category: Chevy
Expert:  George H. replied 4 years ago.

Hello I will help you with your question,

 

There are a couple of possibilities for this problem,

 

This is the manual system of controls?

 

First find the AC clutch relay in the underhood fuse block and use a paperclip to jump the #30 to the #87 sockets in the fuseblock. (Look on the underside of the relay for the numbers)

 

If the clutch clicks in when you turn the key to run then the compressor, the power to the compressor and the wiring for the compressor are good.

 

Let me know what you find and we will work the other side of the system if necessary

 

Thanks

 

 

Customer: replied 4 years ago.

the relay is a small one and the numbers are 2 3

5 1 in that order

Expert:  George H. replied 4 years ago.
jump 3 to 5
Customer: replied 4 years ago.
I jumped 3-5 and still nothing. I know the relay is good though because i used the horn relay in place of it earlier. They are the same relay
Expert:  George H. replied 4 years ago.

If you have a voltmeter or testlight check for voltage at the paperclip and if that is good check at the compressor connector.

 

 

Customer: replied 4 years ago.
My father and I just checked it with his voltage meter. there is two connections for electrical to the compressor one on the top and one in the back. We checked the one on the top earlier and we weren't getting anything form it. I'm not sure what the one on the back goes to cuz the new compressor i bought doesn't have a connection on the back but it has a snap ring that is easily removed but it seems to have a plug underneath.
Expert:  George H. replied 4 years ago.

The rear is the high pressure cutout and is not part of the circuit you are working on. so check the paperclip with the key on and if there is voltage there check the green wire at the compressor. If there is voltage to the compressor and the clutch does not pull in when you plug it in replace the compressor.

 

 

Customer: replied 4 years ago.

It's not reading any volts from the green wire

Expert:  George H. replied 4 years ago.
How about the paperclip?
Customer: replied 4 years ago.
Yes there is voltage coming from the paper clip at the relay panel. but nothing from the green wire at the compressor
Expert:  George H. replied 4 years ago.

Then you have an open in the green wire between the #5 terminal of the relay and the compressor connector. This is a single piece of wire so look for any breaks in the harness and if you cannot find anything overlay a new wire. This takes care of the power to the compressor but to be sure of the repair you need to check the control side and be sure the PCM is turning the relay on by grounding the pin #1 of the relay.

 

The is a splice just where the wire from the compressor connector enters the main engine harness I would start looking there.

 

 

Customer: replied 4 years ago.
I looked at the splice earlier today and found nothing wrong with it so we checked the green wire just before the splice and still got no volts. Im not sure what you mean about this though.............but to be sure of the repair you need to check the control side and be sure the PCM is turning the relay on by grounding the pin #1 of the relay. And I'm also not sure what the PCM is. I desperately need your help and thank you for everything so far
Expert:  George H. replied 4 years ago.

There are two sides to any circuit that has a relay in it. You have just diagnosed the power side that runs from the fuse through the relay contacts to the load (in this case the compressor) . The relay is controlled by the PCM (computer) which grounds pin #1 of the relay to turn it on (or to close the contacts so that power flows to the compressor)

 

For the PCM to ground the relay coil at pin #1 it has to be sure all conditions are correct. The AC switch on the dash has to be turned to on, the pressure of the cycling switch has to be above 40 psi and the high pressure switch on the back of the compressor has to show pressure below 425 psi. If all these conditions are met the PCM grounds the relay and the compressor is turned on.

 

By jumping the relay contacts with the paperclip you did the job of the PCM and found that the power was not reaching the compressor but was present at the relay. Double check that you have the correct pins jumpered and that you don't have power to the compressor connector then find the break in the wire. You may have to expose the wiring harness back to the relay box to find the break

 

Once you have power to the compressor you can install the relay and see if the compressor operates on command from the AC switch. If it does you are done. If it does not we will have to work to find which of the conditions the PCM does not like

 

Let me know what I can do to help you with this

 

Thanks

 

 

Customer: replied 4 years ago.
does it make a difference which way you put the relay in? obviously right? anyway we seem to be getting a connection from the panel to the plug on the compressor but no power to the plug. sorry it took so long to reply, my laptop died on me
Expert:  George H. replied 4 years ago.

It really doesn't matter which way the relay is installed for the four leg relays, I like to look at the tops and keep all the printing the same but when you turn it the contacts just swap ends so the connections remain the same.

 

I'm not sure what you mean by a connection from the panel to the plug? Do you mean you have a complete wire from the paperclip (installed as a jumper between the two corners of the relay sockets (3 and 5) or (#30 and #87)? If you do have a complete wire check for power at the paperclip and at the connector.

 

 

Customer: replied 4 years ago.
okay now I'm not sure which relay sockets are 3 and 5 because i was going by the numbers on the underside of the relay and if it was installed the opposite way then it would be backwards. I tried it both ways and i seem to get connection one way but not the other. it seems to be coming from the bottom left slot where the relay is installed. when the car is cranked and the A/C is turned on there seems to be power to the fuse panel but not the connector.
Expert:  George H. replied 4 years ago.

If the numbers ar in the corners and you have the wide flat side of the relay up with the legs pointing at your face and the 3 is in the upper right with the 5 in the lower left turn the relay 180 degrees so that the side that was pointing up is now down. The 5 will be in the upper right with the 3 in the lower left now. It doesn't matter as long as you start at the 3 or the 5 and use the paper clip to jump diagonally to the other corner.

 

Draw this out on paper if you are not sure

 

 

George H., ASE Certified Technician
Category: Chevy
Satisfied Customers: 16048
Experience: GM Tech ASE Master Tech 15+ years
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