Help diagnose A/C problem
 

yes I have searched and rear tons of threads on this forum and many others as well.

my Z is a 2003 w/ about 75k miles on it. For the past few years it is not driven often (only to, from, and at the track basically). As far as I can remember, the a/c was working just fine and then one day only would blow hot air. I don't think it was a gradual problem.

It is blowing air, but only hot (maybe ambient, but it's hot in Miami). The clutch on the A/C compressor does appear to function (doesn't turn when a/c is off, and turns when a/c is on).

I bought a freon recharge can, and hooked it up to the low-pressure line of the A/C while running on full-blast/full-cold, but the pressure reading was 100psi (way high). It hasn't ever been recharged before should it shouldn't be this high I think. From what I've read online, it can read high if the compressor is not kicking on. But in my case the clutch appears to be operating correctly.

Does the clutch operating on the compressor necessarily indicate that the compressor is functioning correctly, or can it still be broken? Or is there something else I should be looking at?

Crazy because I have the same issue with the clutch turning on and no cold air. I replaced the high line because it had a leak in it. Vacuumed the system and recharged the system with freon. All seems to be working but no cold air.

^ hope you're not stuck driving around FL summer with the Z and no a/c.

one other random thought, my outside temperature reading is showing incorrectly also. it's been reading way lower than actual outside temp, usually around the 50s. could it be a related problem?

some more info..

radiator & condensor fan are working normally. a/c appears to be blowing ambient-ish temp air when set at cold, and blows hot air when set for a hot temperature.

Bueller...

I did some googling - being overcharged with refrigerant can cause a high pressure switch to trip, resulting in no cooling. Seems to fit your high pressure reading.

Thanks Bret. I appreciate the input. I've seen the same about 100psi being too high. That said it is supposed to be around that pressure for static pressure reading. That would point to the compressor not actually working properly, but mine isn't making any funny noises and the clutch is working as it should.

So I'm stuck trying to figure out if there is some other part that could be bad and preventing the refrigerant from being compressed as it should.

I would definitely fix the temp sensor issue. The car uses this temp reading to determine how cold of air to blow. At least in "Auto" mode.

Probably shouldn't have added the refrigerant until checking things a bit more. For example, was the compressor kicking on? Perhaps the control unit inside the cabin isn't working properly, opening up the vents to cold air from the evaporator, rather than warm air from the heater core. Or, the temp sensors inside the cabin may be bad, causing a similar issue. There are actually two different systems - one to cool/heat the air, and the other to distribute that air properly into the cabin. Until you get the system back to a proper refrigerant level, it's going to be tougher to diagnose.

Are there any shops in the area which will provide a "free" a/c check (which of course won't be free in the end, but it's a start)? If I lived in Miami, I'd be getting the a/c fixed ASAP, regardless of $, as it's already hot/humid enough here in Tampa.

I never actually added any refrigerant. I don't know much about a/c systems, but decided it would be the wrong thing to do with the reading at 100psi, as you say.

Compressor kicks on (can hear it clicking on when turning on the A/C, and can see the clutch spinning when A/C is on). I unplugged and replugged the white ribbon cable to the controls just in case it might do something, but nada.

I'm arranging with a friend to swap in his external temp sensor to see if that helps at all (will prob try disconnecting mine tonight and see if anything changes that way also). And can also try swapping his control panel and the white box. Another friend said he can get the proper gauges to check the readings from the high side and low side.

Fortunately I dont have to drive the Z at all. But I've been skipping out on track days because I can't deal with an hour+ drive to and from the track with no A/C during Miami summer.

Appreciate all the brainstorming help so far! Will report back after some more diagnoses.

Sounds like a good plan. If the stuff under the hood is working properly you should be able to feel the hard lines and see that one (hi pressure) is hot and the other (lo pressure) is cold.

The outside temp sensor has nothing to do with how the a/c system works. there is a inside temp sensor that is connected to the a/c system for when you put it on auto.

Evac and recharge the system first then go from there.

my guess would be that the inside temp sensor isn't the problem then, since the air isn't blowing cold even if it is not set to auto.

also noticed tonight that when i push the left control, iirc this would normally turn on the defroster (i think that's for the front). however, that is not happening now. that light never goes on, and the air doesn't blow out of a different vent. turning that knob works as normal though to adjust where the air blows from.

Is the compressor turning on at all? Is it staying on?

My compressor is turning on and staying on but blowing hot air. Bret if the high pressure switch trips, does it have to be reset?

as a follow up..

my friend hooked up the gauges to high and low pressure side, but wasn't able to determine a problem from that.

i ran the self-diagnostic test that is in the service manual. it fails on step-3, which indicates I should replace the A/C Contoller (white box). I continued through the diagnostics and all the temperature sensors were indicated to be working fine (weird since external temp reading is always wrong).

I'm still a bit unsure about the problem just being the a/c controller since the pressure on the low-side never drops to where it should be.

probable course of action.
1) replace the ambient temp sensor since it's relatively cheap anyway.
2) try and convince a buddy to let me swap in his a/c controller to see if that fixes the problem.
3) if 2 fails, then replace a/c compressor assuming internal damage?

any thoughts?

just to keep this going as a log...

today i was able to swap in another a/c controller (needed replacing according to fsm diagnostic). no change unfortunately.

i also tried disconnecting the ambient temp sensor to see what would happen, but no effect from that other than the digital gauge showing icy and ---- for temp. i'm sure that gauge isn't working correctly since it was reading 66 when i had the car on today, and it was more like 85 at the time.

the other sensor that failed the diagnostic test is the sunload sensor. this apparently has some effect on the air mix door and could cause the problem of no cold air i think. i'm not sure if this sensor is actually not working, or if there just wasn't enough sunlight at the time. need to try on the weekend when i can do it middle of the day, or find a 60 watt light i can take outside.

i keep thinking it must be a bad compressor since the low side pressure never drops even when the clutch is engaged. but bc the clutch engages as it should, and there are no weird noises or other signs of the compressor being bad, i'm going to try and rule everything else out first. possibly there is some other blockage in the system? expansion valve?

I'd (quietly - discreetly) push in the schrader valve on the low side and continually recheck the pressure until it drops to 45psi or so and see if suddenly you get cold air.

Your system may be over pressure, which could also indicate a blockage in the lines (as the only way to get a high reading any other way is if someone added coolant beyond spec).

that thought did cross my mind. however, 100 psi on the low side is in line with the static pressure should be. and the system has never been charged before so there is no way it should be over-charged.

it's gonna be a looonnngggg drive to homestead (track day) tomorrow.

I'm on the same mission. Went to a shop to check Freon line and supposedly they added it but for some reason my compressor wasn't getting power. I'm about to add a direct 12v line to the compressor and bypass all these damn sensors and what not. F U 350z with no A/C in Miami!!!