Need help with Air conditioning symptoms

[slightlyevil]

Have my theory of what's gone wrong, but after reading a lot of previous threads on aircon issues, I'm not 100% sure I'm correct. Before I go buying parts I'm hoping the braintrust can help me confirm what's going on. Here's my symptoms:

- When car is running (engine on), and AC is OFF, there is extremely cold air coming from vents. It comes out slowly when care is stationary but comes out more when car is moving.
- Cycling the AC on/off etc does not actually turn stop the cold air, it just changes the vent fan speed and what's on the CCU readout.
- Turn AC/fans on, and it now actively blows cold air out.
- Setting AC to 'auto' and changing temp, the fans come on to push air but the temp stays freezing cold.
- Turn the heat on full, it's still cold air coming out, not really any hot air.
- Fan speed knob does control the fan speed/turn it off with no problem.
- Constant quiet whine coming from engine compartment, changes with engine RPM.

more things I noticed in testing:
- After removing the AC clutch relay, there's no longer any cold air coming through the vents which tells me the compressor clutch isn't stuck in 'engaged'. This was my original theory, dang.
- Trying to cycle through the modes on the CCU it doesn't change the venting location, it only wants to blow out of the main vents not the floor or windshield vents.

 

[Old Guy]

It seems like the AC compressor is permanently engaged. Confirm that it is running even though the AC is turned off. On the presumption that the compressor is permanently running, pull the compressor clutch relay and test it. If the relay tests bad then replace it and check operation. If the relay tests good, then start the car up with the relay removed. If the compressor operates with the clutch relay removed, chances are that the compressor clutch is stuck in the engaged position (not even sure if that is possible). If the compressor does not operate, the compressor relay is ground switched via the ECM. There may be a short to ground on the wire between the relay and the ECM causing the relay to operate or the ECM may be getting a false signal from the CCU (the CCU does not have direct control of the clutch relay).

You could also check the clearance between the compressor pulley and the clutch pressure plate. Absence of clearance would be an indicator that the clutch is stuck in the engaged position although in my exceedingly limited experience, I have never heard of that happening.

 

[slightlyevil]

Thanks for that. I haven't tested the relay yet, but when I pull it, the cold air is gone from the vents, just blowing ambient air, so I assume that means at least the compressor clutch is working. I've noticed though that when I cycle through the different 'modes' on the CCU, the vent doesnt change, it just keeps blowing through the main vents. It won't switch to the floor vents or the windshield vents.

 

[Old Guy]

Run the CCU through its self test mode. If the self test fails, then you have a CCU issue which may not necessarily be the CCU itself. However, given the capacitor issues in the NSX electronics, chances are that the CCU needs the capacitor 'fix'. If it passes the self test, you may still have a CCU problem; but, you need to eliminate the other possible cause for the compressor running which is a false ground on the connection between the compressor relay and the ECM. This presumes that the compressor relay has not welded its contacts in the closed position.

 

[bruckner]

Do condenser fans run with ignition, regardless of what input is on CCU?

 

[Old Guy]

Do condenser fans run with ignition, regardless of what input is on CCU?

Not on my 2000.

The condenser fans are controlled by the cooling fan control unit. Given the age of your car, it may be suffering from the capacitor induced funky electronics blues. Is your rad fan (also controlled by the same unit) running all the time? That might be an indicator of a control unit problem. The fan control unit gets a signal from the CCU so if the CCU is also suffering from the capacitor blues it could have gone south and is sending a false signal to the fan control unit causing it to operate. You will need to go through the diagnostic procedure in the service manual to determine which is causing the problem.

 

[bruckner]

Not on my 2000.

I was asking the OP.

 

[Old Guy]

OK - no, with no reference to 2000 model Yr.

1991 and 2000 systems essentially the same. The fans should not run with just the ignition enabled.

 

[bruckner]

1991 and 2000 systems essentially the same. The fans should not run with just the ignition enabled.

Not asking whether they should or not, asking OP whether they do run. I'm fairly well versed in how these systems "should" work, yet often don't, as is the case here.

 

[Old Guy]

OK, misunderstood the nature of the question.

 

[RandyD]

Same issue with my 91

OK, misunderstood the nature of the question.

Hi I was wondering if you ever found the solution to this problem I am having the same exact problem with my 1991 NSX as well I’ve checked the relays and they are fine?

Thanks