Strange AC behavior I have never seen.

[Chris142]

07 civic 4D with a 1.8L 4 cyl,107F. Ac works good when idling or driving over 35 mph. When driving over 20 mph or under 35 mph the ecm turns the ac clutch off. I evac and charged it to spec.al Also replaced the plugged cabin filter. No change.

I'm stuck on this one.

 

[Cujet]

Wow that is odd I wonder it it's related to a full throttle acceleration cutout.

 

[mattd]

Can you view ac pressure data via scanner while driving? Maybe there is a sensor within that parameter that shares the 5VREF with the ac pressure sensor and it pulls down the voltage intermittently. There has to be some parameter out of spec for the ecm to command the ac off

Are you sure is COMMANDED off and not just showing the clutch is disengaged?

 

[Chris142]

Originally Posted by Cujet
Wow that is odd I wonder it it's related to a full throttle acceleration cutout.

You don't have to mash on it. Just cruising 30 mph= no ac.

 

[AC1DD]

I seem to remember that there was a relay under the hood that becomes defective that results in this situation. Can't remember exact details though.

 

[mk378]

Have you looked at the coolant temperature? Likely a high ECT reading (either genuine or false due to bad sensor) would disable A/C. Hondas do strange things when the cooling system is not full.

This is assuming that it really is the ECU disabling the clutch not the well known lemon relay or the clutch itself.

 

[Chris142]

Originally Posted by mk378
Have you looked at the coolant temperature? Likely a high ECT reading (either genuine or false due to bad sensor) would disable A/C. Hondas do strange things when the cooling system is not full.

This is assuming that it really is the ECU disabling the clutch not the well known lemon relay or the clutch itself.

Coolant 198f. The computer is actually commanding the clutch to go off.

 

[newtoncd8]

Try the compressor clutch coil.

From the Civic forums for a similar problem: "Your compressor clutch coil has begun to fail. Very common problem on these civics. I was a dealer tech for 4 years and I replaced many of these coils. (usually the clutch too) I recommend an aftermarket compressor. The honda parts will be more money than an aftermarket compressor assembly."

p.s. I am not a technician in anyway, just searched a bit. If I am way off, disregard.

 

[Nukeman7]

It is probably a bad or marginal A/C clutch coil assembly. I believe it uses the same compressor as the 2007 CRV which received a warranty extension because of the high failure rate as described in this Technical Service Bulletin:

Honda TSB 12-072

Have you hooked up a test light to see if the clutch electromagnet coil input lead is receiving 12V when the clutch disengages?

 

[clinebarger]

Originally Posted by Chris142

Coolant 198f. The computer is actually commanding the clutch to go off.


Can you monitor the head pressure via a scan tool PID? If not.....You could always monitor the output voltage at the sensor via a T-pin & multimeter.

Below 28 psi (.68vdc) or Above 455 psi (4.57vdc) will cause the PCM to disengage the compressor clutch. A faulty sensor & intermittent shorts to Ground or 5 volt reference can cause these issues.

 

[clinebarger]

There is also a evaporator temp sensor, But I don't have voltage charts for it.

IIRC.....It will cut the A/C Request when the Evap temp gets to low. Where a Pressure Sensor issue does not affect the A/C Request status.

 

[Chris142]

Originally Posted by Nukeman7


Have you hooked up a test light to see if the clutch electromagnet coil input lead is receiving 12V when the clutch disengages?
yes I connected a digital test light to the wire.
Its not the coil. The 12v power is being turned off by the ecm.

 

[Chris142]

Originally Posted by clinebarger
Originally Posted by Chris142

Coolant 198f. The computer is actually commanding the clutch to go off.


Can you monitor the head pressure via a scan tool PID? If not.....You could always monitor the output voltage at the sensor via a T-pin & multimeter.

Below 28 psi (.68vdc) or Above 455 psi (4.57vdc) will cause the PCM to disengage the compressor clutch. A faulty sensor & intermittent shorts to Ground or 5 volt reference can cause these issues.

I taped guages to the windshield. Low was 40-45 psi and high was 230ish.

 

[clinebarger]

I understand the actual pressure readings are OK, You're a professional & never doubted you checked that.

A faulty pressure switch or shorted wiring is what I'm referring to.....The PCM can't see your gauges brother

 

[Chris142]

Originally Posted by clinebarger
I understand the actual pressure readings are OK, You're a professional & never doubted you checked that.

A faulty pressure switch or shorted wiring is what I'm referring to.....The PCM can't see your gauges brother

But why off @20 mph and back on @35 mph like clock work. Not 20 mph one time and 23 the next. 20 and 35 every time and repeatable.

 

[clinebarger]

I don't have a good explanation for that other than the sensor may have some Open &/or Shorted places in the Potensiometer?

Of course.....I'm just pointing out a place to check for faults. The PCM only has a limited number of Inputs for it to disable the A/C clutch relay.....

A/C Request from the control head
ECT to high
A/C head pressure to low or high
WOT operation

 

[Warstud]

Originally Posted by Chris142
Originally Posted by clinebarger
I understand the actual pressure readings are OK, You're a professional & never doubted you checked that.

A faulty pressure switch or shorted wiring is what I'm referring to.....The PCM can't see your gauges brother

But why off @20 mph and back on @35 mph like clock work. Not 20 mph one time and 23 the next. 20 and 35 every time and repeatable.

Maybe designed that way due to overheating under 35 mph.

 

[mattd]

Did you read my post??

 

[Chris142]

Originally Posted by mattd
Did you read my post??

Yep. We dont have that sophisticated of a scanner.

 

[mattd]

Hmm. That may be the only way you're going to find this one.