2004 Civic LX

The a/c seems to work first thing in the morning when it's cool and it blows really cold, but the clutch doesn't engage during the day when it's hot out. I checked all the fuses and swapped the relays, they're all fine. I checked the low side pressure and it's fine. The clutch will engage when there's power to it, so is it a bad pressure cut out switch or thermostat? Are they in series deep down on the compressor? How do I test if these are the culprits, just see if they're receiving voltage and don't have continuity?

Thanks for any help!

 

Get a manifold gauge set and measure the pressures on both the low and high sides. The pressure may be too high on the high side and shutting off the switch. Does the fan run? Is the condenser clean?

 

The fan runs, how do I check if the condenser is clean?

 

View the grill through the hole in the bumper.

 

This is probably the clutch gap, assuming everything else works (fan comes on, engine idles up). When it is hot under the hood, the clutch coil becomes weaker and the gap is more critical.

 

Here's how you would check mk's idea:

 

Thanks for the help, I'll check the clearance. I checked the pressures: 130 low, 125 hi (of course the compressor was not engaged during the readings)

 

Quick update: the clutch clearance is right on, is there a trick to accessing the thermal protector? It's super tight down there.

 

When it does not run, unplug the clutch wire from the car (the wire which goes to the thermal protector first, then the clutch), and measure resistance to ground. You are measuring through the protector and coil, it should be around 3.5 ohms as specified. The protector will be zero ohms if closed.

If that checks out, plug wire back in and backprobe it to see if voltage is present when the compressor is supposed to be running. If you have battery voltage, there's no electrical problem, so close up the clutch gap anyway. You can set it very close as long as the clutch doesn't rattle or drag when off.

 

Ok, update again.

I was wrong before, the compressor is NOT receiving power, the voltage was going to whatever switch is on the compressor and not returning. I jumped the switch and the compressor and fans run fine. The pressures while running: Low side: 50-55 psi, High side: 175 psi, ~85 F outside.

What's in circuit to the other two small wires in the compressor plug that don't power the clutch, pressure switch? thermal switch? Also, what conclusion (if any) can I draw from the high low-side pressure being too high?