Fuzzychaos

From here for testing the HVAC comes the below step.

3. While holding both the switches down, turn the ignition ON (II), then release both switches. The recirculation indicator and the rear window defogger indicator come on. The recirculation indicator goes off 2 seconds later and the A/C indicator comes on (if you have A/C), then the self-diagnostic will begin. About 10 seconds later, the self-diagnostic will finish and the A/C indicator turns off.

So I have AC in my car which is presently not working. Why would the A/C indicator not come on during this test? There is no error reported. Pressing the AC button turns the light on and off without engaging the AC. I've tested all the rest of the hardware that I can find troubleshooting steps for and the clutch can be forced to engage by shorting the relay socket in the right place.

I fail at step #13 with voltage on the red wire here.

My ECU has been replaced with a junkyard front end collision and reprogrammed by Honda. Does that mean that they forgot to 'enable' AC in my ECU during the programming?

Fuzzychaos

So it's 2 years later and still never was able to get this fixed

Anyone have any idea what would make the heater control panel think that there is no AC in the car? Turning the A/C on and off by pressing the button causes the light to turn on and off but the diagnostic check doesn't turn it on. Is there a signal controlling this?

Fuzzychaos

Funny, went out to pull the multiplexer and low and behold the AC light comes on, when it was pulled down out of the holder. So now it works properly during the self diagnostic check Now on to other checks since it still isn't getting the AC clutch to engage.

Former User

When you press the A/C button, do the radiator and condenser fans turn on?

Fuzzychaos

Yes the fans turn on properly now. The problem is the compressor thermal switch is not working, after jumping it the compressor clutch engages. The heater console AC button turns the clutch on and off correctly.

It also had a faulty engine temperature sensor and the fans weren't turning on when they should which caused the head gasket to blow when the engine overheated while driving about 1500 miles, after the engine temperature sensor was replaced the fans turn on normally now.

The next issue is that it still doesn't blow cold air. Honda troubleshot the AC and said the thermal switch was bad a long time ago (even though they didn't find the fault with the multiplexer, I could only confirm this after the multiplexer started working. They also said there's no leaks and the pressure switch shows a short which is somewhere in the good range.

I will perform a pressure check with an AC manifold and see if there is correct pressure and the conditions of the high and low side to check for blockages. I'll remove the blower as well to see if I can see the condition of the evaporator. The condenser fins are little damaged but since the fans are working I was expecting the AC should blow even a little cold air.

Any other suggestions to check the AC?

In a few days we'll start working on the head gasket replacement once the engine is out (will get a few things done at the same time), replace rad, cleaning, gearbox bearings...

Fuzzychaos

So while we had the engine out to replace the head gasket we replaced the expansion valve (just in case it was bad) and later connected a new dryer/accumulator at the AC shop and did the vacuum and recharge (oil done first). The AC works correctly now. The only issue is that we noticed a very very small leak at the manifold on the high pressure line going into the expansion valve before any work was done. That is on the engine side of the firewall. That leak got quite a bit worse with the high pressure and it's bad with a very slow leak. Not sure it can be fixed without replacing that huge 2 hose assembly.