Bad AC Compressor?

[Carbo]

For the past few weeks, my '97 Civic has been idling rough, almost bucking you might say, whenever it's am idling and the AC is on. The AC is blowing nice and cold, and when I'm driving there are no issues. But as soon as I hit the red light or slow down the rough idling starts again, almost to the point of stalling. It feels as if the compressor is kicking on and off.
Any ideas? Thank you.

 

[exdeath]

How low does the idle drop when stopped with AC on and does it jump back up when the AC is turned off?

Compressor is fine if it's blowing cold. Compressor clutch is fine if it goes away when the AC isn't on.

Sounds like an AC idle up switch isn't working. AC and power steering have aux idle control valves that open up and allow air to bypass the throttle to increase engine idle when AC or power steering are in use. This is to compensate for the severe loads placed on the engine and prevent the engine from stalling at idle.

 

[Carbo]

Shut the AC off and the idle smooths out and is steady at about 700 rpm. With it on, idle flucuates wildly as the compressor kicks on and off.
When driving, the AC blows ice cold.
Idle switch? I'll look into this. Also, I was thinking the fan on the AC side might be the problem.

 

[Bartman39]

Agreed (with exdeath)...:thumbsup: Sounds more like an engine issue and not compensating for the AC compressor being engauged...? IAC...? (Idle Air Control) Not sure if that car has one but should being EFI...

 

[Carbo]

Took a look at things this morning. What I noticed is the condensor fan isn't turning when the AC is on. I have to assume this is the issue.
Is the replacement the entire fan assembly: shroud, fan, and motor? Or just the motor? How manageable is this repair for a do-it-yourselfer?

 

[5150MyU]

Should be just motor and blade-you can hook up a test light to see if fan should be powering up.
Or bench test the fan.

 

[Carbo]

Don't have any of the the necessary equipment you describe. It's probably best if I bring it to a local shop.

 

[5150MyU]

NAPA test light 12-15dollars that will let you diagnois it-radioshack DVOM-18-24dollars--save you big bucks if you do it yourself.

 

[5150MyU]

If it is a single fan unplug the TWO wire connecter and connect a test light between the two pigtail wires-it should light within 20-30 seconds with the A/C on-if it doesn't you have other issuses.

 

[brblx]

get a cheap DMM from sears or even harbor freight. test light works too, but it's more useful to have a meter.

as stated, see if there is voltage and ground at the fan connector with the AC on. if there is, the fan is bad. if not, locate the fan relay and see if it is coming on. if it's not, check voltage and ground at the relay control terminals. if that's good, it's the relay, if it's not, the PCM is probably not commanding the fan on.

the fan issue itself should not cause the idle issue. it'll cause the AC to be warm, as the high side will overpressurize, but this generally doesn't have much effect on engine idle other than the compressor cycles a lot more, which could cause a lot of variation but not poor running, unless the engine is just very sensitive to the increased load of the 250-300psi+ high side.

it seems odd that the AC is cold. it should be warm with the car stopped, if you feel the low side lines they might get a little cold but the high side lines will be scalding hot. with gauges, the system pressures will read like it is overpressurized, but it's just a lack of cooling of the high side which results in a low side that is unable to cope (causing warm evaporator/warm air from vents).

the car may have an additional fan for the AC on the front of the radiator. are you sure that no fan is running?