Yugo Splattski

I have a 2008 Civic 1.8L engine, When the ambient temp is above 105, the a/c pressures are 30L/250H at idle. And stays there. A/c working great. Then when I simulate a 70mph at 2500rpms the pressure reach 20L/325H when it cycles off. By the way I have a Floor fan in front of the condenser when simulating. It will cycle this way Reach 325High off. 250High back on. Then I take away floor fan and drop rpms to idle. To simulate doing 70mph and then hitting stop traffic on free way then idling. The clutch cycles off then take a very long time for the pressure to drop to 250H to cycle on. and the condenser fans have kicked off when the clutch did. and i'm idling with no air flow thru condener. Then i put floor fan in front of condenser and the pressures will drop quickly and cycle back on. I would think if the condenser fans stayed on at that high 325 at idle it would drop way faster. i changed a/c pressure switch and temp sensor. I have read the a/c pressure sw is what works fans. should these fans be on.?

ezone

High pressure cutout spec is around 455 PSI.
Your 325 shouldn't be excessively high pressure.
I'd be checking this value on my scanner to make sure the pressure sensor is accurate with the PCM..

What's your coolant temp when the AC is shut off? The AC will be shut off if it sees an overheat condition.


Speaking of coolant temp, there are known problems with the temp sensor and wiring in the bottom of the radiator. The sensor can leak through the pins, corrode the wire terminals, and cause codes, and possibly mimic an overheat condition to the computer.


Thermal protector went open circuit?
How about the evap temp sensor, is it accurate?

Fans should be on low speed whenever the compressor clutch is engaged. The AC pressure sensor (NOT a traditional switch) gives pressure data to the PCM to prohibit operation at very low and very high pressures, and switch the fans to high speed-- typically around 210-230 PSI.


HTH

Yugo Splattski

When it is 105 deg. or higher the pressures are higher. I know this is normal.In the evening or a cooler day system works good.The pressures are lower. The engine temp never gets over 190. thermo protector ok.
What is exactly happening to me is When im comming home in rush hr. get on freeway I go approx. 70mph at 2500 rpms. then i hit the usual traffic , dead stop and idle my way on freeway for some time. This is when the a/c stops blowing cold. So i simulated the same situation in my driveway to see what was happening. and I found that when the pressure is at 325 and comp. cycles off the condenser fans cycle off with the compressor and the preesure drops very slow to reach 250 to cycle back on. at a idle without the forced air or condenser fans. The engine temp is ok and the compressor temp is under 210. I believe the refrigerant is to warm and needs the condenser fans to stay running even though the compressor is cycled off the fans stay on and there is no problem, But they cycle off with the compressor. And at a idle without the forced air the pressure just sits or drops slowly. At a idle the system is very happy sits at 30/250 it is when i come from 70mph to a idle and the pressure is built up

Yugo Splattski

Fans should be on low speed whenever the compressor clutch is engaged. The AC pressure sensor (NOT a traditional switch) gives pressure data to the PCM to prohibit operation at very low and very high pressures, and switch the fans to high speed-- typically around 210-230 PSI.

I have not noticed 2 speeds at any time. They seem to be at high when the compressor kicks on. I just read somewhere that the pressure switch is a 3 funtional switch. Turns comp. off at 455 hi or 28 lo and kicks fans to hi above 255psi Mabe im missing the 2nd speed in the fans, But they still run when the compressor is on, when the compressor cycles off the pressure is above 255psi , should the fans stay on in 2nd speed and are not?

ezone

Ok maybe no? I got that info from a general Honda application chart, not specific to Civic.


On your model car it's not a switch. It's a 3-wire pressure sensor, capable of telling the PCM actual high side pressure data at all times.

My wiring diagram shows
low speed fan control coming from terminal A4 in the PCM, and
high speed fan control coming from terminal A5 in the PCM.
There's more than just those wires involved, but there is provision for both low and high speed operation.

I'm staring at wiring diagrams, I can't check an actual car here:
Once the compressor cycles off, the fan control is given to the radiator temp and engine coolant temp sensors.. So if the coolant temp is not high, the fans shut off when the compressor clutch is shut off.


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If your system repeatedly hits 325 and shuts down, I wonder what the PCM is seeing from the high pressure sensor? (GOOD scanner needed to see that value!)
Is the data value true and accurate??
If you had some wiring issue causing incorrect output value (voltage) from the high side pressure sensor, I might better understand your car doing what you described.

I also wonder what value the PCM is seeing for ECT2 (again need a good scanner), the temp sensor in the bottom of the radiator.

And AC request signal and clutch control signal, and fan control high and low signals.


I don't know for certain which scanners can give the data values I mentioned, as I am able to use Hondas HDS scanner for this.

HTH

Yugo Splattski

Once the compressor cycles off, the fan control is given to the radiator temp and engine coolant temp sensors.. So if the coolant temp is not high, the fans shut off when the compressor clutch is shut off.

I ran it again last night, when sun was down and the temp was lower and the comp. cycled off at lower pressure and the fans stayed on almost all the way to cycled on , shut off for a brief moment. until the comp cycled on and they came back on,
You say the fan control is given to the radiator temp sensor. the one in the bottom of the radiator? Thats the only one I haven't changed yet.

ezone

Not quite what I said:

the fan control is given to the radiator temp and engine coolant temp sensors..

Text is vague about which one operates the fans. I assume it's the one in the radiator, but I didn't see that in print.
It could even use both for all I know-- one having priority over the other, like a backup system.


Pull the connector off that temp sensor and inspect the terminals for wetness and/or corrosion? Most of the time when I have seen those have a problem there was a code related to open circuit and very LOW temp noticed in the data...

...but if that sensor were to fail with a false high temp reading.....