masongardner

Hey guys, long time lurker, but first post for me. Need some help from the experts on here. 2007 Civic Ex A/C issue.


My problem is that my compressor runs ALL the time. Doesn't matter if the A/C is on or off, doesn't matter if the defrost is on or off. Doesn't matter if the temp is set to hot or cold. Doesn't even matter if the air is turned completely off. My compressor is always running. It is always engaged and never releases. And in this process it freezes the low pressure line and stops blowing any air out of my vents, hot or cold.


The main thing is that the compressor and A/C work fine in the city, but 5 minutes or so on the interstate and the lines are frozen solid. I am assuming this is because the clutch is always engaged and it is spinning so fast on the interstate that it freezes over quickly.


I have done some searching on other threads and a few things before just jumping on here to ask.


I swapped relays with the a/c clutch relay, didn't make a difference, so I am guessing the relay is not bad (thought I am going to buy a new one tomorrow just in case),


I unplugged the compressor from the top of the alternator and of course it shuts off, along with the fan.


The other thing I did, I was hoping this would point to being the problem, was I unplugged the control panel inside the car. When I did this, the compressor released and was not running. I was trying to find what controls the compressor, telling it when it needs to be working or at rest. I don't mind replacing parts, but don't want to go replacing everything if I don't need too.


Thanks for your time and info, hopefully get this thing fixed here pretty soon.

Star1967

Puzzling does it make any odd sounds? Kinda like whirring sound or a scraping?

Star1967

Have you tried cleaning the switch on the console? A little compressed air might dislodge dust and or debri. Also you might try plugging a toggle switch or click button to see if it is a bad switch it might just be a simple $5 fix.

ezone

Wait, you said it still runs the AC even when the panel is turned off? Needs the control panel.

masongardner

I have not tried cleaning it, are you thinking that maybe the switch it stuck down or something? I will pull the panel apart tomorrow and take a look at it. When your talking about a toggle switch, do you mean replacing say the A/C button with a toggle to see if its bad? Does say the A/C button have more signal output to the compressor than the max a/c or visa-versa? Thanks!!

masongardner

I did the self diagnosis both when it was running correctly and when it was frozen over and no codes either time.


The compressor runs when I have the air switched completely off, but when I unplug the control panel the compressor clutch releases and the fan turns off.

ezone

Needs the HVAC control panel.

masongardner

Is the evap temp sensor the one behind the glovebox somewhere? Maybe I will take a shot at that tomorrow also, assuming its not too expensive. Going to replace the relay (5 bucks) and see if that does anything. I don't think it will since I swapped with the fan relay and nothing changed, but you never know.

ezone

Don't waste $5 on a relay, don't waste coin on the temp sensor either.


The HVAC control panel is bad. Replace it.

masongardner

Is it a common problem with these guys? I hope its as easy as replacing 1 part. That would be nice.

ezone

Apparently it is becoming more and more common as they age.

I've only seen one 8th gen car with a bad HVAC control unit (the panel) at work so far this year, but there have been several more found bad on the forums.

masongardner

Cool, ill see if the local junkyard has one tomorrow, if not, amazon or ebay. Thanks for the help. I will be sure to report back.

masongardner

I'm sure somebody knows, but what is it that tells the compressor clutch to engage and disengage before it freezes. Temp sensor aomewhere?

ezone

If your control panel were working correctly, the evaporator temp sensor would tell the panel what the temperature in the core is, and the panel decides when to cycle the compressor off and on. (cycles at roughly 36-42 degrees or so, high enough so it does not freeze up)

As it stands now, your control panel is bad keeping the compressor running all the time --- even when the panel is turned off.

(The panel failure is actually keeping the "AC Request" signal to the PCM turned on, the PCM is what operates the compressor and fans based on that request.)


The compressor (and fans) shut off when you unplugged the panel so it's not a stuck relay causing it.



I'd have no problem replacing the HVAC control panel based on what you have written.

masongardner

Finally have a day off work tomorrow, going to try to find a panel in my area and replace it. Thanks for the info, always curious on how this stuff works.

masongardner

Big shout out to you guys! Looks like the hvac panel I got from the junkyard fixed my problem! I can commute in a cool car now (without it freezing over). THANKS YOU GUYS!

masongardner

You were spot on!! Thanks for the help!

ezone

YW

tdwpgtp

I hate to revive an old thread, but I'm not making any progress on my car. It seems to have all the same symptoms EXCEPT it continues to run after I unplug the control panel.Unplugging the compressor plug near the alternator turns the system off, as does removing the relay, and when I cut the wire from the PCM to the relay box (to cross out the possibility the wire shorting to the chassis somewhere). I ran a temporary new wire from the PCM to the relay and the compressor and fans still ran.

Any other ideas? Is there anything else that can command the PCM to give the AC relay ground? Is there anything between the heater control panel and the PCM that could cause an issue?

ezone

Because the PCM is part of the system: hvac > pcm > compressor

I'd plug in my scanner and view live data.......see the status of AC REQUEST (y/n) and see if the PCM is actually commanding the clutch relay and fans to be on, or off.
THEN I use that info to decide my next checks.

tdwpgtp

Is that something I can do with my cheapo bluetooth scanner, or do I need a real scanner?

Additionally, I DID replace the multiplex unit, since it was 15 bucks at a junk yard. So far it seems to have fixed the issue, but since it has always been intermittent, I am going to give it some time. HOWEVER, now with the new multiplex unit, the keyless entry no longer works. There shouldn't be any programming that needs to be done for the multiplex, correct? I did notice that the original fuse box had a fuse for heated seats, even though the car never had heated seats, and the new one does not have contacts for a fuse there. Is it possible that they used the heated seats fuse for the keyless entry receiver? Or is there something else I am missing?

ezone

I have no clue what data your cheapo unit is capable of.

If it worked before you replaced the fusebox but now it does not, logic says whatever you did has everything to do with why it doesn't work now.
Wrong fusebox? (IIRC there was something like 15-20 different part numbers in the Honda parts catalog over 5 model years)
Wire plug not fully seated in the box (or missing)?
Fuse(s) not in the correct slot(s)?

BTW in earlier reply I may have just assumed you have a 2006 or newer car because this thread is 8th/9th gen, not 7th gen.