[rl968]

My AC had always worked well, until recently. Doesn't blow cold. System is charged, compressor works, fan kicks on, fuses fine and all controls at the dash work. Looks like a wiring issue. I have the wiring diagram, but wondering if there is a common procedure to follow and what to look at first. Thx

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[MB968]

Can we assume from your comment that the compressor works, that you can observe the clutch engaging on the compressor? And, you know the system is still charged, because there are no bubbles in the sight glass when the unit is operating. Or you've put a gauge on the high pressure line and see the right pressure.

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[psuphoto]

Just curious, how do you know its charged? Is it possible it has a new leak since it was charged?

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[rl968]

Compressor works, gauge used, no leaks. It's a wiring issue, where to start?

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[tamathumper]

Do you always get hot, or just no cold? Clark's Garage has a series of troubleshooters on common AC problems. Try HVAC-02 to start.

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[MB968]

Haven't been to the Clarks gar., but usually a very good resource.



Another simple check, assuming it is electrical, will allow you to confirm that the system is functioning correctly. Check the wiring diagrams to be sure, but normally the clutch on the compressor is already grounded. Maybe someone else here can confirm, but I've never seen any compressor that wasn't wired this way. So, when you turn the a/c on, it powers the line running to the clutch/compressor with 12 v. To check the clutch, you can pull the single line that goes to the compressor. Use a fuse in-line wire (in case there is a short, it will blow the in-line fuse) to connect this line to the hot side of the battery. This should engage the clutch/compressor; and allow you to check the system with the engine running. As long as the clutch engages and turns the compressor, you should get cold air. This will at least tell you that the basic system is functional and you just need to trace why the 12 volts isn't getting to the clutch.

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[gbarrier]

You say gauges. What are the pressures? Does the compressor stay on? Blower motor working? Give us something to work with here.

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[madridcab]

What about the heater valve, is it working, or constant heat?

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[rl968]

Compressor is not getting 12v. There is a break somewhere I think, or a bad relay.

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[rl968]

Anyone know how to remove the dash HVAC control unit? I think there is a bad ground in there. When I push AC button it lights up and I can feel compressor kick on, but I think there might be an issue with the temp control or the unit itself. Defrost also not kicking on cold air. Just a guess since I know compressor works and holds a charge.

[quote name='madridcab' timestamp='1371764386' post='144645']What about the heater valve, is it working, or constant heat?[/quote]



How can I tell if heater valve is an issue? Where is it located?

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[tamathumper]

If you have issues with temp control but the unit appears to function and the compressor kicks on, have you checked the tube that connects the little round grille in the dash to the air temperature sensor on the inside of the firewall?

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[rl968]

I see the grill next to cig lighter, but How do you access inside of firewall and get behind the grill?

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[tamathumper]

As I recall, if you remove the glovebox you should be able to see both ends of the tube. There is also a very small screw inside the little round grill if you want to take off the dash ribbon that it's in - there's a procedure on Clark's Garage for that as it's very easy but not intuitive (there are covered screws).

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[DaveN]

Little covered grille spins about 20-30 degrees ccw (?) and pops out to reveal the screw.

I find that temp sensor hose, at least on my S2 and 968, about 1 cm too short to stay on with pressure - probably shrunk with age. I had to stick a tie-wrap about mid span to stop the hose from sagging and falling off one end or the other.

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[rl968]

What does that hose do that would cause AC not to work?

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[DaveN]

It samples the ambient air in the car and feeds the climate control with that air. There is a small fan (reportedly) at the end of the tube and if it get plugged or stops turning the A/C has no idea what temp the cabin is and therefore starts to warm or chill you to the wrong levels.

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[rl968]

pulled the cover, dont see much, looks like a hole leading to nowhere. what am I supposed to see? removed the screw but that did nothing. does glove box need to come out to get bettet view?



could there also be a problem with the temp control switch in dash? how do you get at the unit? remove vent and instrument panel?

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[DaveN]

You have to remove the glove box to see the hose attached to the vent circle; it could have come off the A/C control unit. The A/C unit comes off with just 4 screws after you remove the knobs and the filler plate. Be careful if you remove the unit as the tabs are quite brittle and may crack if you tighten the screws too much upon installation.

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[Cloud9...68]

Is this the tube you guys are talking about?:



   



Mine fell out when I was poking around under the dash a couple of years ago when I was preparing to pull my engine. If this is the correct tube, and if I understand the posts in this thread correctly, I need to remove the glove box, which will give me access to the back of the little round grill in the dash. The other end of the tube goes into air temperature sensor on the inside of the firewall. I think this is correct, at least in theory. Does anyone happen to have a picture of the air temperature sensor (aka AC control unit), showing me where it's located? From the descriptions, it sounds pretty easy to find, though. Also, does the end closest to the accordion section of the tube go into the little round grill, or the AC control unit? Thanks.

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[DaveN]

That's the tube. It's pretty easy to find out where it attaches to the A/C. As I recall the end of the hose is almost directly behind the little front grille connection with just a slight "S" bend upwards with the accordion part being the front (cabin) connection.

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