Rick3452

Yesterday, as always great ICE COLD AC, today I went to get gas and NO AC. Clutch is not engageing. What should I look for??
Thanks... Rick

rixter

"ice cold" as in TOO COLD?.. a sign it's low on freon, not positve on early MYs but later have a sensor which disables the clutch when too low as to keep it from frying IIRC

wish I could help more, I'm sure one of the ac gurus will jump in though

SharkSkin

Freeze switch will allow it to operate until it gets too cold. This is the little device under the rainshild on the HVAC housing that has two wires and a capillary tube on it. First check your fuse and relay, then the freeze switch(should have +12V on either side) then the low pressure switch which should be on the dryer. Also should see +12V on both terminals of that switch.

Schocki

Ice Cold first and then no AC at all? I would bet the relay inside the control unit (center console) is not doing it's job anymore. Best option is to take the old relay out and run a couple of wires to a sturdier external relay.

Before you pull the unit check for current to the freeze protection switch. If you have no current there it is most likely the relay.
If there is current then check the low pressure switch for current. Low pressure switch has current,but no voltage to Ac clutch? Bad switch or low on charge. switch is good on both sides? Then check the AC clutch.

Here is the post: https://rennlist.com/forums/showthre...dioshack+relay

Giovanni

With no AC, do you mean no Cold air or do you mean it does not blow air at all??? If it does not blow any air most likely it is the relay. Mine does that too from time to time (controller is switched ON but no air and AC light button is pressed does not light up). I just tab on the relay panel and cold air again. Hmm, maybe I need a new ac relay but heck.

SharkSkin

Schocki's got the scoop on the control head relay. First check at the freeze switch for +12V at either terminal on the freeze switch with engine running and AC switched on If you're getting +12V on either terminal, consider that relay replacement to be a potential upgrade of secondary importance. Starting at the freeze switch will quickly tell you if the problem is in the passenger space or in the engine compartmant.

Wally Plumley has a great write-up here. Be sure you check the fuse; I don't see where Wally mentions it in diagnosing that circuit, but there is a fuse you need to check as well. I see another goof, the early cars (77-79 IIRC) won't activate the compressor clutch without the engine running. Oh well... I'll send Wally a PM.

Rick3452

Thanks for all the great ideas, I will post the outcome on this thread.
Rick

Rick3452

Hey guys, Just checked freeze switch, only hot on one side (drivers side) when running and AC on. What does this tell you experts..

Schocki

Simple: That's where your problem is unless you have multiple issues. Take the switch out and check if it works. Clean the contacts...
You can also bridge the switch for a couple of days. But you risk that the evaporator freezes to a solid block of ice :-)
You will fell this when the airflow gets low and warm. Just turn the AC off for a couple of minutes and the ice will melt.
If the switch is shot get a new or used unit from Mark Anderson...

Rick3452

Schocki,
Thanks for the quick reply. I did disconect the two wire from the switch and put a wire between them. tried several times, confirmed that the one side is still hot. But did not work. Any other iseas?? Thanks..Rick

Lorenfb

Make sure that the A/C compressor clutch wire is not shorted to ground and
that the clutch resistince is not less than 4 to 5 ohms. If either of these
conditions is NOT true, the climate control unit will be damaged.

mark kibort

disconnect the wires leading to the pressure control unit under the hood, but in the area at the base of the windshield. a bunch of spade terminals attached there . turn on the AC and then disconnect a terminal and re connect it . You should hear the clutch engage and the AC turn cold. i had this issue, and it was intermittant. it would alwasy work, but i had to do this process occasionally.
just an idea.
MK

dr bob

"...confirmed that one side is still hot." This tells me that your jumper isn't doing the job, if in fact you are saying that one side is still hot and the other side is not. If that's the case, make a short jumper wire with 1/4" male spade connectors, insert it in the circuit in place of the freeze switch. This will completely eliminate the freeze switch from the circuit. Does the clutch engage now? If not, get out the voltmeter again and measure the voltage at the jumper, reference to ground. With engine running and AC button engaged, you would normally see +12V. If you see no voltage at all, start with fuses. If the voltage is low, look at the relay in the control head. If you see 12V or more, you need to move downstream to the pressure switch and possibly to the clutch coil itself.

The current flows through the control relay, to the freeze switch, through the 16-pin connector by the jump-start terminal, through the pressure switch near the receiver/dryer, to the clutch coil on the compressor. Diagnose from top to bottom with the voltmeter, and you'll easily see where the circuit is broken or weak.

Many "problems" with 928 AC systems are tied to leaks. There are many more leaks than there are electrical problems, so before you go deep into electrical troubleshooting, consider putting a set of AC pressure gauges on the car to see if the freon level is too low due to leaks. The pressure switch is in the high-pressure circuit of the system, so in many cases the compressor will start with a very minimum of gas in the system. Once it starts, the compressor will cause the high-side pressure to rise, fooling the switch. That initial pressure, before the compressor starts, is a function of how much gas is in there, but much more related to ambient temperature. A warmer day will give you more pressure than a cooler day. Is "failure day" a cooler day than the last time you ran the system successfully? This would point me to a low freon problem, and would cause me to put the gauges on right after I checked a fuse or two.

HTH!

macreel

Rick3452... be sure your vacuum connections are
good, especially at the left fender, by the
brake booster; i.e., nothing broken/disconnected.


G'luck.

Schocki

Rick,
Just like Dr bob said in his post about the sequence of switches that are energized. That's how you search for the problem.
I would recommend to jump the switch with a fused cable and connectors that fit!

You can also check if the connection between the "cold" side of your freeze protection switch and the low pressure cut-out switch (nearby drier) is still good.