Hi all,

I have a 2001 Honda Civic EX, 5mt coupe. Have had some issues in the past and you guys have been a huge help...hoping the same again!

Anyway, my AC recently stopped working. I dug through the forums and did the simple stuff. Jumped the switch side of the relay and the compressor kicks right on...so no issue with the clutch solenoid. Dug from there into the pressure switch which tested continuity as it sat there...refrigerant is good. Probed the relay terminals and found 12v on one side of the relay solenoid to ground on the battery but the opposing terminal would not go to ground after pressing the switch. (open to ground regardless of switch) The switch inside the car glows green and appears to be working yet no go. I tried to find continuity between said 'dead' relay connector to ECU/PCU red wire in connector E behind the glove compartment. Could not get a reading there but it's cramped so not a whole lot of confidence in my measurements.

Anyway, has anyone else had this issue? I've read sometime the entire multiplex interior fuse panel goes bad but I'm not having issues with locks, windows, security or CELs.
Also have read some potential issues with the blower motor transistor but my blower seems to be working just fine.

Also, I do not hear any 'relay' type click inside the car when pushing the AC button. I cannot recall now, but does your car 'click' when you push the button? (Is there a relay in the car I am overlooking?)

Any and all suggestions are much appreciated! Thanks for the help!

 

When the button is pressed, the control panel pulls the wire to the pressure switch (I think it is blue) to ground. If the switch is closed, this signal passes through to the MCU which then sends a multiplexed signal to the ECU. Then the ECU turns on the relays for the compressor and fans.

So you should measure voltage at the pressure switch while pressing the button on and off. If the voltage goes to near zero on both wires, control panel is OK and the MCU or ECU or relay or fuse for the relay is the problem. If voltage doesn't change, run the control panel self test. It could be the evaporator temperature sensor, which is connected to the control panel. When the sensor detects the evaporator is colder than 40 F, the control panel will cycle off the compressor, though the light in the button will remain lit.

When the ECU gets the command to start the compressor, first it increases the idle speed slightly. This can be a way to tell if the MCU is working.

Do not jumper stuff to force the compressor on. Running the compressor without the condenser fans will quickly create a dangerous overpressure that can blow a hose or the compressor.

 

Thanks for the info mk378!

Yep, you are right about the overpressure. I just needed to see if the clutch was working so I jumped it for all of 5 seconds.

Anyway, I just measured the voltage at the pressure switch relative to the neg side of the battery I find this. One side is always hot running 12-13v irregardless of ac button. The other side shows open when measuring voltage and open in continuity to neg, but when the ac button is pushed (light on) this terminal goes continuity to the battery. (ground)

So since I do indeed have voltage at one terminal and not the other does that mean it's my control panel? If the voltage goes to near zero on both wires, control panel is OK

I'll have to look up the control panel self test and then give that a try next.

Let me tell you this though...so it's winter here in Minnesota and it's been cold for a while...well below 40 F for many days. So I don't need the AC so much for cooling, I need it to defrost my windows when the car is full of warm breathing people. So I'm wondering if the unit is always below 40F, what implications does that have? Is my ECU looped in an off cycle?

I also tried the simple, RPM test. Usually when the AC would kick in there would be a noticeable drop in RPM plug a dog on the car...that's how I noticed the AC was out...no dog in performance or RPM when the switch was applied. Paying careful attention this time, I turned the blower on medium and pressed and released, pressed and released the AC button. It lights up each time but I did not notice any change...not even a marginal one.

Thanks again so much for your thoughts and experience. I sincerely do appreciate the help and your generosity! Any other key things for me to check other than the control panel self test?

Thanks again!

 

Man mk378, you know your stuff! I'm impressed!

Anyway, found your instruction on how to run the diagnostics. Ran it (kinda fun how the HVAC system does a little dog and pony show at that moment) but had no blinking lights. Guess that means my system is cool but more I read the more I think perhaps the cold temperatures are messing with me.

Thanks again and further thoughts?

 

Voltage change on one side of the switch but not the other means that the switch is open (or the plug is not making contact). The switch will open normally in cold conditions because all the refrigerant has condensed and the vapor pressure of the refrigerant is too low to close the switch (50 psi, corresponds to about 45 F I think). That is probably the case here. Bottom line is the A/C will not engage while the outdoor temperature is below freezing. Performance can't be evaluated very well except in hot weather anyway.

So I'd say quit worrying about it until spring. In cold weather run the defroster with outside air not recirculated.

 

Thanks again MK, you're right on.

So today we had a heat wave in Minnesota...this usually happens when it snows. Temperatures today topped out near 25F today (Down right balmy) and I let my car idle for a while in the parking lot to see if I could warm everything up enough to test some ideal gas law. It must have gotten warm enough build pressure or to unfreeze something because the system did kick in today. Compressor clutch and condenser fan ran like normal. Thank goodness! No spendy car parts! (I also closed the internal damper to heat up the evap switch inside the car.)

Feel kinda stupid for chasing a dead end but learned a lesson today. Thanks again for your support and advice now I just hope anyone else that happens upon this issue in the tundra is able to fine the answer here.

Thanks again!

 

Hey I'm new to this site. I just bought a 2000 Honda civic Si without an a/c compressor on it. The guy said that it quit working so he took it off. The rest of the a/c system is still there. I just bought a new a/c compressor and drier. Should I replace anything else since the lines have been open for probably about a year now. I think I might replace the expansion valve too, but I was talking to a guy at a tire shop that mentioned something about replacing the one of the a/c hoses because it has a part in there that you cannot buy separately. Can anyone tell me what I need to replace besides the compressor and drier? Thanks.

 

im going throuhg the same project right now as well. i went to NAPA to get parts and the guy at the counter said if you are going to get a new compressor you will need to get the drier and evaporator to get the 2 year waranty. the compressor was a refurb and cost about 340 but the drier and evaporator were an extra 40 bucks more. so with everything it came out to about 380. and i get the 2 year warranty. hope this helps.