Hello all.

I have benefited a lot from this forum over the past few years, but finally had a need to become a member and ask a question. So here it goes. Bear with me for being detailed and long winded!

In 2010 we bought a 1996 Civic LX, and the air conditioning worked great at the time. Sometime in 2011 it quit, and I never really did any diagnosis until summer 2012. I confirmed it had a bad condenser fan motor. Then waited until I had the radiator out in summer of 2013 to replace the fan. So the condenser fan works great now. While replacing the fan I noticed that some of the wires looked jerry-rigged, (possibly making the compressor run from the fan relay) and the new fan had untampered wiring, so I swapped the wiring and new motor over because the fan frame was bent on the junkyard fan. So the wiring is all back to factory.

The bearing in the pulley on the ac compressor completely gave out about a year after the AC quit, so I had to cut the belt, and now it has a new clutch and pulley, and the air gap is correctly in spec. I checked the wire running into the compressor from the plug to the compressor case and got a reading of 4.7 ohms.

I have replaced the expansion valve, and the low pressure switch, neither of which has helped.

After replacing these, I had the system vacuumed down to 29, and filled with R134A. The guy that did it didn't use a machine (which I was NOT happy about), so I have no idea how much exactly he put in. He used two 12 ounce bottles, so it should be fairly close as I think it's supposed to take 22.9 oz maximum, 21.2 oz. minimum. I don't know if that could cause the problem or not, being 1.1 oz. overfull. Is that possible? I am thinking about having a good shop evacuate it and put in the precise amount with a machine. They want $60 to do this.

So, here is my diagnosis so far. I have checked the fuses and they are both good, #17, and #56. When I push the AC button it lights up green and the engine revs up a bit like it should, and then settles down because the compressor clutch is not kicking on. So I have tried jumping the low pressure switch, and that does nothing, only make the idle go up. When the LPS connector is disconnected the engine does not rev up when the AC button is pushed.

There is only one thing I have been able to do to get the compressor clutch to come on. When I jump the terminals on the compressor clutch relay, the compressor immediately engages, and the air blown out is cold. But as soon as I remove the jumper, the compressor shuts off. I swapped the condenser fan relay into the slot for the compressor clutch relay, and that did nothing. Still no ac clutch. The condenser fan stays on the whole time as long as the AC button is on.

I am pretty sure that the thermal protector is not the problem as it is wired inline before the compressor clutch, and the clutch works when jumped, so I don't think that's the problem. Please correct me if I am wrong about this.

The one thing I haven't tried is checking the pins at the ECU. If I understood correctly, the engine idling up when the AC button is pushed indicates that the ECU is giving the signal to engage the compressor clutch. But again, I may be wrong, so if anybody could clarify this that would be great!

I am pretty frustrated having followed the diagnostics on this forum and others and still not being able to figure out why it doesn't turn on. If anybody could help, that would be greatly appreciated!

Thanks!

 

The ECU may be bad. If you ground ECU pin A17 (Blk/Red wire), does the clutch engage?

 

THANK YOU SO MUCH!!! The compressor clutch does indeed engage when I grounded out A17. I am so relieved to have found the problem after 3 years!!!

I guess I will be shopping for a used ECU.

MANY THANKS AGAIN!!!

 

 

Update: I got a used computer from eBay for $41 shipped. Plugged it in and the AC works! Praise the Lord!

I did have the blower motor go bad, and got a junkyard one for $15. So now everything works!

One last question. Should I have a shop check the R134a level since I don't know how much is in it, or is it fine to leave it since it seems to be working well?

 

I wouldn't do anything if the A/C blows cold.

 

Ok, thanks!