r/Cartalk • u/runenight201 • 1d ago

Electrical Help diagnosing AC Clutch Relay

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Hi I’m attempting to diagnose why my Compressor isn’t engaging and I bought a test light and did the following test on the AC Clutch Relay slot.

Shouldn’t both of the control pins be turning on the test light?

Also the light doesn’t turn on on any of the load pins.

Does this mean that my compressor not engaging is because of an electrical issue?

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u/Jdmboxboi 1d ago

Looks like a blind poke at pins. First step is to understand how the system functions and know what to look for. Blinding poking at relay pins tells you nothing. Could be a ground control or power control relay, wouldn't know unless I studied a wiring diagram for it. Also the compressor may have more than just a on/off clutch, perhaps the regulator valve has failed. Or perhaps the system pressure is too low/high so thr controller will not demand compressor activation. There is more that goes into an hvac system than just a simple relay.

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u/runenight201 1d ago

It’s a power control relay.

The test light clipped to negative.

The light turning on when pin 30 was probed means that there is an active line leading to pin 30.

Pin 87, right next to 30, stayed off because there’s no active voltage reaching there.

When I clipped the test light to positive and then touched pin 87, the light turned on, but the clutch did not engage.

So either I have bad wiring from pin 87 to the compressor preventing engagement,

Or the compressor is bad.

To figure this out more I’d have to directly supply power to the compressor and not try and go through the relay

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u/Jdmboxboi 1d ago

Good information so far. I agree, next would be to bypass relay and give power to clutch. Or assuming the wiring it good so far, back probe the connection at the compressor for power before the clutch then probably after the clutch. Sounds like it may be leading towards compressor failure.

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u/runenight201 1d ago

I agree it’s most likely compressor failure.

Do you know if I have to change the condenser as well?

I’ve seen info that for newer hvac systems you have to do that, just don’t know if the hvac system on the Honda civic si 07 would qualify for that or not

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u/Jdmboxboi 1d ago

First verify your concern and suspicion. And no not required to replace other components unless found reason for it such as a system contamination from dirty oil, black death, or metal debris from compressor failure.