1990 Honda Accord intermitent A/C problems


I have a 1990 Honda Accord. I’m having problems with the a/c unit. In the early AM when I switch on the A/C, clutch does not engage and only blows hot un-conditioned air. After about 20 minutes of driving I can feel the compressor clutch engage and the A/C starts to work and blow cold conditioned air. The a/c has been checked out for leaks. None were found. They find nothing wrong with ac unit. Any advice?


The a/c has been checked out for leaks. None were found. They find nothing wrong with ac unit.

Who were they and what all did they check? If it was not an A/C shop, I would suggest taking it to a A/C shop, not just a shop that also does A/C work.


It was an A/C shop and they weren’t able to duplicate the problem. The A/C worked perfectly in the shop.


This may be near impossible to figure from my vantage point but here’s a few possibilities.

One, the most likely IMHO, would be the thermoswitch that is located between the AC switch and the compressor. This is temp dependent and could go stupid.
This could also be bypassed with a jumper wire for test purposes to see if the problem disappears.

The other is trickier. The compressor relay is controlled by the ECM, or engine controls computer.
Maybe it’s possible a temp sender has gone stupid or there’s an internal fault in the ECM. This would be hard to verify unless the AC is inoperative in the hands of whomever is checking it.

It would be easier to jump the thermoswitch and see if the problem goes away. If it does, that should answer the question. Hope some of that helps anyway.


Thanks for the replies. I’ve noticed that as soon as the A/C button is turned on, both fans operate but the
clutch on the compressor does not engage until after 20-30 mins. The A/C mechanics told me the fans working as they should.


With both fans operating when the AC button is energized, I’ll revise my earlier theory; a.k.a, wild guessing. :slight_smile:

I made reference to a thermoswitch previously. After taking a look at a schematic, if the thermoswitch is defective the fans will be inoperative.

When the engine is cold and the AC is inop. the red/blue wire at the compressor relay should be checked to see if it is grounded. The ground is provided through the ECM.
The comp. relay wiring is coded this way.
Black/yellow on TWO terminals should power up with the key in the ON position.

The red wire at the relay should have power with the AC on, and ONLY if the red/blue wire is grounded through the ECM.

The red/blue wire at the relay should have power and ground through the ECM. This is what triggers the comp. relay.

About all I could recommend is the wiring I listed checks out when the engine is cold and the AC is inoperative.

With an intermittent, the problem would likely fall on a faulty comp. relay, ECM glitch, a burned or corroded wire connector at the relay or clutch coil, or possibly a faulty compressor clutch coil.
Hope that helps anyway.


Thank Ok4450 for narrowing down the list of possible problems with my a/c.


Can you leave it at the A/C shop overnight? It sounds like whatever the problem is, the engine has to be stone cold for it to show.


I might have to just that.


ok4450 you were in the ball park. The A/C specialists diagnosed a faulty compressor relay switch. They topped off the system with about 7 ounces of R12 and added oil to the compressor and it works like new again. Thank you all for your help.