A/C compressor stuck "On"

[georgeNCSUee]

Hi there!

I recently got a 95 240SX SE , wrecked, totally stock, and I am in the process of fixing it before I start with the mods (if I ever do). Right now I am trying to solve the A/C problem that's giving me headaches (and low mpg #) and although I searched around, I can't seem to find an answer for. What happens is I cannot turn the A/C off. It works ok (meaning that I can turn the compressor on and off as I please) the first half a minute or so after I start the engine after it’s been off for a while but after that, once the ignition switch is turned to 'ON', the compressor clutch engages and doesn't disengage until the ignition is switched off. It doesn't care if the A/C main switch is 'ON' or 'OFF' or what speed the fan switch is, or what button of the air direction control is pressed.

What I know for sure is that the push control unit gets power, the lights, fan speed control, and air direction control work, and when I turn the A/C switch on and off, the condenser fan starts and stops and the engine rpm increase and decrease a little, like they are supposed to, but the compressor stays engaged. If I disconnect the push control unit harness, the clutch still remains engaged. Taking out the A/C relay or disconnecting the pressure switch does disengage the compressor. I do not believe it’s a stuck A/C relay since I measured it and it looks good, and it clicks when the compressor engages.

Anyone, please help! The stock KA is weak enough without the A/C drag, but here in NC it’s still way too hot in the middle of the day to just take out the relay. Plus, I have to have everything work right, or else what’s the point of having it.

Thanks for any input!

George

[NISTECH]

It sounds as if it is stuck in defrost mode. Anytime a climate control system is set to defrost it engages the compressor.

[georgeNCSUee]

Any idea which component of the system would cause that problem? And when the A/C controls are disconnected, the compressor should be disengaged, right? Since my compressor remains engaged even with the controls disconnected, does that mean that the A/C control unit is OK and the problem is somewhere else (like the ECU)?

[NISTECH]

Try swapping the relay with another of the same kind. See if that makes a difference. It could be the relay is hanging on once it is engaged.

[georgeNCSUee]

Right on, man! The relay was the problem even though I measured it and all. I feel extremely newbieish.

But the most puzzling thing is that after I replaced the A/C relay with the fog lights one (they were the same type), the fog lights still work right. Weird or what?

Thanks again!

[NISTECH]

less of a load on the relay. It will likely cause it to hang up again sometime down the road. IIRC its the blue relay which is like 12bucks at the dealer. I would suggest picking one up just in case.

[georgeNCSUee]

Well, it seems that the problem is not totally fixed. Actually, I do not think it was the relay (yes, it was the blue one). The thing is, I not sure if it's starting to get stuck again or if whatever part was causing the problem in the first place is returning to normal operation. Now, after I turn off the A/C, the clutch remains engaged for a little while but after that it disengages. I am going to further monitor this to see if the 'stuck time' get longer or shorter. But if it begins to stay stuck 'on' all the time, what do you think the problem could be? Thanks!

[NISTECH]

Your gonna have to see if the compressor is actually getting a voltage when it is stuck. You do this by back probing the connector on the compressor. It may very well be the clutch disc is dragging on the clutch assembly allowing it to stay engauged. This would be due to improper shimming of the clutch disc [pretty rare for that to happen]