I have a complex AC problem in my Civic. I need to tell you the story so that you might get a potential diagnosis of the issue:
- Car started having problems with AC in 2015. After driving for a while, the evaporator would freeze (blowing ice pieces to your face), then no longer would get cool air (after ice clogged evaporator completely).
- Once that happened, I would turn off the AC and keep fan on to melt ice, then turn AC back on... I kept doing this for most of 2015 until...
- On 2016 it finally died completely. It would not engage, the clutch would not kick in (compressor not spinning), and obviously I would not get any cool air.
- Took it to a mechanic, they said it was a bad compressor, replaced the compressor and recharged the system, and $1300.00 later I was happy with my AC working and cooling fine, but...
- I didn't use car for 3 days, on 4th day I start the car and guess what? No AC, no clutch engaging, no cool air. I took it to the same mechanic (they have a 1-year warranty on the work...) and they told me they were not able to figure out the problem... and to bring it back other day and leave it. Fine, I haven't brought it back until I get more information myself. Somehow I suspect they didn't do a right diagnostic the first time, and perhaps I paid $1300 to change a compressor that was not really the root cause!
- I take it to a HONDA dealership, they say is the ECM/computer... they come up with some weird story that there is oil in the ECM connector and the computer is leaking oil? Seriously? I don't buy that crap. So I start doing my investigation and reading about AC myself. Of course, the dealership wanted to charge me $900 to replace the ECM which scared me away immediately.
Here's my investigation after reading about Civic 2007 electrical circuits, AC, sensors and so forth:
- All fuses are OK and working. I tested every single one in the AC circuits.
- The relay that kicks in the compressor/clutch is fine. I tested it outside the car, using power-supply and multimeter.
- The clutch is not the problem, I manually verified that it engages. Now, when I jumper the high-current terminals to force the clutch/compressor, it almost makes the engine stall. It sounds like the compressor cannot add any more pressure into the system, or there is some obstruction (at least that's my theory). Another possibility is that the new compressor is broken as well? Who knows.
- FYI, the relay that kicks in the AC is controlled by a ground enabled by the ECM/computer. That signal is never received as the clutch never engages, the relay is good, and I verified continuity from the relay terminal to the ECM pin. Apparently the ECM is simply protecting the system due to input from some other sensor, perhaps that the pressure is too hight in the system?
- I also need to mention that when you start the AC in the dashboard panel, the cabin blower starts as expected. However, the AC condenser and radiator fans are not engaged (both should come on), instead they remain off (again, this should also be that the ECM is not sending the signal).
- With the car completely off, the pressure readings I get are 113 PSI(low side), 110 PSI (high side) which I really don't understand much. I can't read any dynamic pressure as the compressor is not kicking in as mentioned.
Update 8/23: The cabin self-diagnostic function (tests control unit, blower, air mix and mode motors, evaporator temp sensor) detected no issues. So I guess that rules out any problem with the control unit or evaporator temperature sensor.
Now, having said all this, what is the most likely root cause of the problem? Bad pressure sensor? Bad evaporator temperature sensor? Problem in the evaporator valve or orifice tube? Any way to check the previous components?
Now, there is a remote possibility that indeed it is the computer. Is there any way to check if that's the case?