Sab

I recently started to have some AC problems, where the compressor does not come on.

I replaced the relay in the control unit and had the system evacuated and refilled.

It seemed fine at first, but now the compressor stopps again intermittently.

What else could cause the clutch to disengage? Once the clutch kicks out I tried to jump the high pressure switch and no change. I fed power to the cable that goes to the clutch and it kicks in and AC works.

We rechecked the system pressure and it reads 37 at idle and 27 at high RPM if I remember correctly.

dr bob

The power goes from the relay in the head, through the freeze switch under the cowl at the base of the windshield. Goes through the pressure switch, then back through that multi-pin electrical connector by the jump-start terminal at the right fender by the radiator, then through a single-pin connector just above/forward of the compressor, where the engine harness passes across the front of the engine. That single lead drops through the compressor bracket to connect to the clutch.

So where are you injecting the 12V to test?


Also-- the pressure switch is in the high pressure side of the system. Should be in the 150PSI range when the system is in service/running.

HTH!

Sab

thanks Bob, I was injecting power at the connector in from of the timing belt tensioner.

Does anyone have a troubleshooting guide for the AC. Where it should have what power...

This is driving me nuts, I just wanted to check it and now the AC works and is ice cold. And this after I have been roasting in the car all day.

SharkSkin

Start here: https://www.928gt.com/T-WallyHVAC.aspx

Sab

Thanks Dave, got it.

The antifreeze switch has 12 volts on both connectors as soon as the AC button is pressed (motor running or not).

Now the confusing part...
The pressure switch has about three volt on one side and almost nothing regardless if the AC is turned on or off.

Right now AC is ice cold. Am I looking at the wrong pressure switch? Right on top of the high pressure connector, correct?

SharkSkin

You may be looking at the pressure sensor sensor switch, #19 in the diagram attached. From the wiring diagram, it seems to be a variable resistance to ground, so your reading seems to check out. Try checking at #17, the low pressure switch. If you're not getting a signal past that point, then you may be low on freon or have a bad switch. Either way it'll take AC service equipment to diagnose further.

Sab

thanks Dave, I checked the wrong switch...

So hopefully it's the low pressure switch. I did already check system pressure and it seems fine.

After evac-ing the system and refilling, how much if any oil should go back in?

SteveG

If you evaculated properly, high is on the dryer and low is under the intake tube passenger side, you shouldn't have lost any oil. Was there evidence of oil leaking? If so, it is a waste to refill it with refrigerant w/o fixing the leak, and to be sure about oil drain the comprssor and refill, too much is as bad as too little. If no oil was evident before, you should be good to go; but then why was it low in the first place?? Are you saying you now have the correct pressures when the engine is running (2000 rpm) and the system on high? You might try a PM to Wally or Dozman, they might have the oil capacity, I think it is only 3-4 oz and takes a special injector tool,unless you remove the compressor; the fitting is the same schrader as the freon. RE freon, my system with rear air takes 37 oz.

SharkSkin

Not sure about the oil, but I've been told it depends on how much oil you've got trapped in the system already, which has to be estimated... even if you pull the compressor and tip it to drain all of the oil out that you can.

Sab

OK, the system was never low on freon. But when we started to troubleshoot it seemed as if the low pressure valve had a leak (hissing noise when removing the blue cap). So we changed the valve. It looked as if my tech took out the valve before the system was completely evaced and some messy and sticky stuff sprayed out. I also had some dye in nthere to see if any leaks are aparent.

Now it was not enough to really make a puddle, but I lost somethin other then 134a.

How would I go about making sure there is the right amount of oil in there?

I guess I will have to evac the system yet again if it really turns out that the low pressure switch is toats.

If the system is evacuated from the low pressure valve, do you loose enough oil for it needing replenishment?

SteveG

If it was evacuated correctly, you shouldn't lose any oil. To my knowledge, the only substances in the system are refrigerant and oil. As to the sticky stuff, that sounds like what happens when 134 is contaminated with R12. But I'm not sure. I do know it is a different oil and you can't just evac R12 and put in 134, it has to be flushed, some say all seals have to be changed. If there is sticky stuff in there, and it circulates, it will clog the expansion valve and/or interfere with the operation of the condenser and evap. If it works at all, you can get brass caps for the valves, but you said you replaced the valve?

dr bob

The pressure switch screws on to a fitting that has a schraeder valve in it. You can take the switch off, and the schraeder valve will close to prevent loss of gas. No evac/recharge required, assuming that the valve isn't damaged.

DIY trick: That switch/valve port is a very convenient place to attach the vacuum pump, for those of us that don't have a recycling/evec/fill machine. Pull vac from there, and you can evacuate the charging manifold and hoses all the way to the bottle.

FWIW, I have --NEVER-- seen one of these switches fail. They often get replaced by folks who refuse to believe that the car leaked out a full charge of gas in a few days or less. The gauges tell the true story.

Sab

OK, I found the leak.
It is in the worst possible place. It seems to be in the high pressure hose going from the dryer towards the passenger sideand then back towards the firewall.
It seems to leak from the compression fitting and not from the seal at the screw connection.

How in the world will I get that line / hose out of there and back in? t seems you have to take half of the engine out to replace it.

Any way to fix that without removal? Or any tips on how to go about this?

This obviously had to happen just as we are getting into the high 80's here again...

Thanks,

bdstott

Am I the only one that thought of this when I read the thread title?

Sab

what?