I have a 95 Blazer LS 4-door. The A/C clutch is not getting power. I can power the clutch with a direct wire, but no matter what I do, no power to the cable. I tried to jumper the low pressure switch, and I replaced/swapped the 3 relays on the firewall; no luck. The fan does blow, and the fuse in the panel is okay. I put my manifold gauges on the system and it is charged correctly. I must be missing something. Can anyone help me. The Haynes manual has nothing on the wiring of the A/C system. I have seen other postings about the 3 relays and what the wiring is for them, but the threads never seem to actually show the information.

Thanks,

Brian

 

If the high pressure switch is triggered, it will lock out the clutch.

What happens when you power it directly at the clutch with a fused jumper wire?

 

The clutch will engage if I power it directly.

 

Test the low pressure cut out switch for an open condition. If it is open, it has been triggered. You either have a high pressure condition in the system or you have a failed switch.

 

I pulled the low pressure connector and jumped it out. It did not engage the clutch. Still no power at the clutch wires. Just FYI, when I put my manifold gauges on the system, the low side shows @ 65 and the high side is @ 60 or 65 (hard to read a real accurate number on the high side of my gauge). Can I jump out the high side signal? Do any of the 3 relays on the firewall control this? I know that the relay on the right controls the blower fan because when I pulled it out, the fan stopped.

 

You can jumper the connector for the high side switch or test the switch for continuity with a multimeter.

There is a relay for the A/C compressor on the firewall. It should be the center one if I remember correctly.

 

So I will assume that the relay on the left is where the pressure switch reports. If it does not engage, then the middle will not engage (in series). The high pressure switch is the plug on the compressor housing behind the belt/pulley flange, correct? Could the connector to the low pressure switch be bad?

 

You only have one relay for the compressor clutch. You should also have a relay for the HVAC fan high speed and one for the intake manifold tuning valve. If you have 4 relays, then the one closest to the passenger side is for the CHMSL (center high mount stop lamp).

Correct. The high pressure switch is located in the back of the compressor.

Does the connector look bad?

Neither of the cut out switches control the relay. This relay is on when the key is on (powered through Fuse 4 - Gauges). The power for the switched side of the relay comes through Fuse 6 - HTR A/C, runs into the HVAC controls, then through the low pressure cut out switch into Pin 30 of the relay. From there, the power goes out Pin 87 when the relay is energized, through the high pressure cut out switch, and on to the compressor clutch.

 

Thanks. I will try it and let you know.

 

The high side connector plastic housing is broken. Also, one of the prongs looks burnt. I tried to jumper it anyway, and the compressor clutch closed for a moment and then shut off again. Now it will not work again. I think it blew the relay. The 25 Amp fuse did not blow, and the blower still works.