Seeking advice on car A/C repair

This is in regard to a 2004 Corolla. This car has always had a slow leak in the A/C system, and needed refrigerant added every few years since new. I took it to the dealer for service a few times while it was under warranty, and within the Toyota Care extended warranty, but they never found or fixed the leak.

That being said, the current problem is that although there is refrigerant, the compressor is not pumping. I connected my set of automotive A/C gauges, the pressures are equalized at 120 psi, and the ambient is 97 degrees today. I tried unplugging and re-plugging the 4-pin dual pressure switch, and the engine RPMs decrease if I unplug the pressure switch and increase if I plug it back in. The pressures on the gauges do not change. (See pictures.)

Any advice to troubleshoot this would be appreciated. I am a professional HVAC technician, so “take it to a shop” is not what I’m looking to hear. Thank you.

Leaks: No personal diy’er AC experience myself, but I’ve heard say a common source of AC leaks are the ports where the test and fill equipment connects to the system.

Compressor not running: Is the AC clutch-on signal present?

You need to check all the fuses related to the ac compressor

then use your digital multimeter and the wiring diagram to verify the pressure switches are working properly

I’d find a good independent a/c shop.

OK, granted you wrote that the leak was a slow leak and that you are a “professional HVAC technician” With that thought in mind, I will not tease you with some unwanted, unsavory comments concerning your qualifications as I am a Computer Programmer, Systems Analysis, with all the requisite Microsoft Certifications as well as numerous CompTIA IT Certifications and as I type this, I am also reloading the wife’s Laptop Computer for the third time today and I cannot figure out why I keep getting some really “flaky” error messages…

As you wrote, it’s a slow leak, but my first suggestion si the cheapest and it is to make up a cup of really soapy water and cover the high and low pressure valves. Even a slow leak might start making a bubble.

Next, then there are the combination Leak Sealer that contains a UV Dye, a cheap alternative to what’s next, but you would also need UV Blacklight Flashlight (less than $10 at Harbor Freight…). But like you wrote, it’s a slow leak and you would need to be patient… ON the plus side of this, the can is also a Leak Sealer and it might fix the leak before it ever leak enough to show. ONE WARNING, be very careful when attaching the connector, if it leaks the dye sprays on everything and it’ll be the devil to discern where the leak really is located.

Finally, and still assuming this is driving you crazy (which I can understand). The question is the leak too slow for the use of an Electronic Refrigerant Detector? I know these are really expensive, but I gotta ask can you borrow one, if not from an employer, possibly from the distributer that supplies your equipment and supplies. My wife once worked for RE Michels, a huge distributer of air conditioning, heating, and refrigeration equipment. She also sold testing instruments. she told me this that they loaned out test equipment and specialized tools to the Good Customers and for the “not so Good Customers,” they had to rent the stuff…

That would suggest the PCM is enabling the compressor but there is a malfunction with the clutch, replay, fuse or wiring. First step, check for power to the A/C compressor clutch.

Is the light in the A/C button flashing?

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I don’t understand. You have a problem that has proven very hard to solve, and you’d rather have the advice of random strangers on a general interest car forum than a/c experts?

Maybe he is asking for replies from A/C technicians, not people that give up so easily and go to a repair shop. Some members have said there are many experienced auto technicians on the message board.

You don’t say whether the compressor clutch is engaging. If it is, then the compressor has failed. If it does not, then basic diagnosis with a voltmeter and wiring diagram is the next step. Check for + and - at the clutch and work backwards from there. A/C clutch relay failure is a common problem for that era, enough so that I always kept 3 in stock at the shop.

Obviously low refrigerant isn’t the problem.

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That’s called knowing your limits. Of course there are good technicians on this board, not the point. He’s one , he’s stumped, dealer’s stumped, time to find the best you can and get hands on the problem.

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I don’t know if he has started to diagnose the problem and the dealer never had the opportunity to diagnose this problem. Years ago, the vehicle was taken to the dealer because of a loss of refrigerant, the gauges show that there is sufficient pressure for the compressor to engage, a leak is not the problem.

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I ended up having to take an after-hours service call, now I am home, and I just looked at the car again. If I start the engine, and the A/C is off, the compressor clutch is disengaged (the center hub does not move). If I turn on the A/C, the indicator light on the A/C button lights up solid, the engine RPMs increase, and the compressor clutch stays disengaged (the center hub still does not move).

I see value in tackling a problem you don’t yet know how to solve. Some people find doing so satisfying and you may learn something.


Start the car, turn on the A/C, tap the clutch hub with a broomstick.


Step 1 would be to check for 12 volts at the a/c clutch connector. If no, move on to step 2. If yes, disconnect and reconnect that connector 3 or 4 times to wipe the contacts. If still no clutch engagement check for continuity through the clutch coil. If no continuity, the clutch is bad.
Step 2
120 psi should be enough pressure to close the pressure switch, so probe for 12v on both input and output sides of the switch. If 12v only on one side of switch, tap switch gently with handle end of screwdriver. If that doesn’t work, replace pressure switch.

I’m assuming in all of this that you’ve first checked for 12volts on both sides of the A/C fuse.

I have not tested anything electrical yet. I will try to find the time to do that today…

Just for the heck of it check the air gap of the clutch. if it is too big it will not engage. I have had this happen in the past.


Any developments?

Haven’t had time to look at the car, as I am working crazy long hours right now. I stopped at home to eat, and to get out of the 103 degree heat for a little bit, but I still have at least two more service calls. I plan to look at the Corolla over the 3-day weekend.

Overtime is great, isn’t it? Hopefully if you’re on call this weekend it’s holiday double pay. Someone has to keep the HVAC systems of the world running. I’m glad it’s someone with the integrity you have.

Stay cool my friend, and let us know what you find on the Corolla.