Seeking advice on car A/C repair

OT is great . . . up to a point

I’ve known WAY too many guys that worked too much OT right up until the point that their bodies rebelled and permanent damage was done

I no longer do OT as I want to preserve what I’ve got

I need the weekends to recover

I’m not going to be one of those guys to go out on early medical disability

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Auto-mechanics seems like one of the most physically demanding jobs there is. Even more so than plumbers and construction workers. Good for you DB for setting your priorities!

For diy’er like me it’s not nearly as much of a burden b/c if I get tired I put everything aside and wait until the next day or the next week to continue. As the folks here probably know I hold the record here for taking the longest time to rebuild a carburetor. And It took me 3 weeks to replace the water pump on my Corolla … lol …

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I believe all your under hood relays are interchangeable. So when you turn on the AC, do both fans run? If they do, then first check for a fuse to the compressor and check it. Next, swap the compressor relay with one of the fan relays and see if the compressor runs but one or both fans do not.

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I am looking at the car right now. I unplugged the 2-pin compressor clutch plug and then started the engine. I observed that with the A/C switched on, everything happens as expected, including the radiator fan coming on constantly, however the power to the compressor clutch is only about 0.8 to 0.95 VDC (constantly fluctuating). With the A/C switched off, the power to the compressor clutch is only a few mV.

I did not see any fuses or relays other than the fuse/relay box in the engine compartment, and there is nothing there designated as “A/C” or similar. There may be another fuse/relay box in this car, not sure where. Edit: I found a YouTube video which shows where, going to check them now…

There’s got to be an A/C clutch relay in the junction box. That’s where I would go first. Can you get a wiring diagram from alldatadiy or someplace like that? This is a very easy circuit to diagnose.

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I am posting to update the solution. The relay is defective. I checked the fuse, it was ok, then I pulled the relay, and surmised that the two thin steel contacts are the coil, and the two thick copper contacts are the normally open contacts. With the ignition off, I had stray volts (less than 0.3 V DC) across the coil pins, and across the contact pins in the fuse/relay panel.

With the engine running, and the A/C turned on, I measured about 13.89 V DC. I decided to grab a piece of solid-core copper wire, bend it into a U shape, and jumper the contact pins, and the compressor activated, and the A/C started blowing cold air.

I am going to order a new relay online, and that should permanently solve the problem.

Also, although I did not observe a blinking light on the A/C button, or any other abnormal operation other than the compressor not engaging, there is a service bulletin regarding this relay from the OEM, which is Denso.

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You should be able to just run down to NAPA and get a new one. Sometimes, depending, there are other relays in the box with the same number that you can swap out as a test anyway.

Glad you solved the problem so easily.

I would say the relay is faulty. Defective implies the part failed while still under warranty, or in its expected lifespan. At 18 years of regular use it’s not unusual the relay failed. Would you expect a residential HVAC relay to last that long?

Good for you for getting to the bottom of the problem OP. Keep on monitoring the situation for a while, b/c the relay may have failed b/c of a lurking problem in the compressor clutch. The compressor clutch may require too much current to activate for example. That could happen if windings of its electro-magnet has partially shorted out.