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


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.


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.

I am updating this thread because warm weather is here, and soon the A/C will be needed. This is my wife’s car, so “roll down the windows and save fuel” is not an option if it’s over 85 degrees outside.

The current problem is that the compressor is defective and not pumping correctly. The clutch engages, and the inner hub turns, but there is only a small pressure difference between the low and high side.

I want to repair this as cheaply as possible, while using good quality parts which will last. And yes, I am a professional HVAC technician (though not automotive), so I have the tools and training to properly recover the refrigerant into a disposal tank and to pressure-test and evacuate the system upon reassembly.

A quick look on Rock Auto shows that the following options are available for the complete kit:

  1. UAC KT3993A Includes A/C Condenser, Gasket Set and A/C Refrigerant Oil; 10S15L Style 2nd Design UAC KT3993A
  2. UAC KT3994A Includes A/C Condenser, Gasket Set and A/C Refrigerant Oil; 10S15L Style 1st Design
  3. GPD 9642549A Includes A/C Condenser and Gasket Set; Compressor Prefilled w/ OE-Specified Oil 10S17L Style; 6 Groove Pulley

I have no idea what is meant by “1st design” or “2nd design”, and this is not obvious by looking at the pictures. Which of these would you buy for this car, or a different kit from some other vendor?

If I recall there may be a difference with how the suction and discharge hoses attach to the compressor. Or maybe the pulley size. If at all possible, grab the Denso number off the current compressor and see if a cross-reference can help you.

I would also replace the expansion valve while you are doing this repair. Also make sure you know if the new compressor is shipped oiled or dry, and add only the proper oil if needed.

I used to get A/C kits from 1-800-Radiator and found them to be of good quality. Might save yourself shipping if they have an outlet in town near you.

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The Denso part number on the compressor is MC447220-4351. The car was manufactured 01/2004, and was built by NUMMI. This is not the Toyota part number, and the other numbers on the label cannot be read without pulling the compressor.

I am planning to buy the kit which comes with the TXV, condenser coil, and gasket set. Some versions come with the oil charged into the compressor, others come with a sealed bottle, and I assume you just pour it in before connecting the compressor.

I am also going to replace the radiator and upper hose (again) since there is a small coolant leak, and replacing the hose and hose clamp did not stop it.

Only ever add the appropriate amount of oil according to the service manual, which is the total system capacity and will include the residual oil in the evap core and condenser. Don’t add the whole bottle. There’s only one thing worse than an A/C system that’s underoiled. And that’s an A/C system that’s overoiled.

With all this work you’re looking at why don’t you just trade the car in on a new one? I can tell from here that you’re anxious to do that! :laughing: :laughing: :laughing:

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ROTFL. This is the only new car I have ever owned in my life, and it has the features and equipment I like. The chances I would ever sell this car are pretty much nil. The only way this car is leaving me is if it’s destroyed in an accident, or if my wife leaves me and takes the car.

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Are you sure you’re not interested in trading up to something like this?

I just found this old pic of a customer’s car. He worked at a Euro dealership but commuted to work in an old Dodge. Perhaps a distant cousin of yours?

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I keep my old cell phones around for quick web searches and their cameras. I have attached an old cell phone to a Flexible rod and I put the cell phone on video and move the phone into places I can reach or see. Sometimes auxiliary lighting is necessary… Perhaps this is all you need to see those other numbers…

It is also great when you drop a part, socket, bolt, etc… and it did not hit the floor…