78 280z A/C Problem

[NewGuy146]

I have a 78 280z and I get no power to the A/C compressor when I turn the A/C knob on. The last owner said that it worked but didn't blow very cold air and thought that the system needed charging. Took the car in for service and the mechanic said that he couldn't get the compressor to kick on - no power. Not very familiar with A/C systems thought I would ask for things to look for in trouble shooting this problem. Trying to get this solved before the good ole Southern heat kicks in.

Also, does anyone know of a good shop in Birmingham, AL that may be able to help?

Thanks!!

[Wade Nelson]

Find an Auto AC shop with good references. The AC compressor won't kick on if the low or high pressure switches in the system are tripped, meaning you've either lost all your R-12, or the system has gotten air/water in it contaminating your R-12.

AC Systems don't "need charging." Ever. What they need is leaks repaired, even very slow ones. Since R12 is no longer available you'll find it a lot cheaper just to install a FRESH compressor and dryer/receiver, and go with a R134 upgrade. Last one pound "can" of R12 I saw went for $150, and you'll need 2-3. A new compressor, dryer, AND several cans of R134 are cheaper!

The new dryer/receiver will soak up any moisture in the lines and condensor remaining after pulling a vacuum on it -- assuming you've fixed all other leaks. It's usually not compressor efficiency, but contaminants that keep systems from getting nice and cold, the old receiver is saturated -- which is to be expected after 30 years.

A R-134 conversion, done PROPERLY, will give you nice cold air. But you really need to find a dedicated AC shop, not just "Joe Mechanic" who has an AC machine. I learned all this after wasting hundreds of dollars on mechanics who claimed to do AC service but were amateurs. I leanred what it took to DO IT RIGHT - including an expensive "micron pump" and gauge that can pull a vacuum resembling outer space!

The best part about R-134 is it's cheap, so if your mechanic doesn't get it right the FIRST time, it won't cost you another $300 to recharge it a SECOND time after correcting leaks.

[Wade Nelson]

p.s. Never, ever use R-134 with "leak stop" in it, which a lot of backyarders do trying to do their own R134 conversion. After injecting leak stop into your system no AC shop will ever touch it. It will screw up their very expensive equipment. And "leak stop" doesn't work in a 300 psi system anyway.

[ZCurves]

Before you start taking things apart, you should first diagnose what is wrong.

Try this:

Check all of your Fuses.

With the engine off, connect a wire to the wire on the compressor, next touch it to the POS side of your battery. It should engage, you will hear it.

Key on On position, test the Pressure Switch by jumping the leads on the harness with a wire - If the compressor clutch is getting a signal, then it will click as it engages.

Using a wiring diagram (available on this forum or at Prospero's Garage) test the A/C relay located under the black cover next to the battery.

You can also test the Fan Switch in the dash the same way.

Once the compressor is engaged, you can then see if it is cooling -and if not, come back and re-read Wade's post or search mine on the topic. We'll get you fixed up.

[NewGuy146]

I'm a newbee so I'm guessing the pressure switch is the A/C control know in the console? I'll work out the other suggestions this weekend and see what I find and reply back.

Thanks for the quick responses.

[sblake01]

The pressure switch is under the hood, usually screwed into the receiver/drier on a factory system.

[hr369]

thats very good advise. that stop leak gums up everything

p.s. Never, ever use R-134 with "leak stop" in it, which a lot of backyarders do trying to do their own R134 conversion. After injecting leak stop into your system no AC shop will ever touch it. It will screw up their very expensive equipment. And "leak stop" doesn't work in a 300 psi system anyway.

[NewGuy146]

Ok here is what I found or didn't find. I used a wire and touched the battery with the contact coming from the compressor and it clicked. I then searched for the pressure switch and didn't see anything that was connected to the receiver/dryer. I also followed the wires from the console control through the firewall and found it didn't connect to anything.

That was also true about the wire coming from the compressor. It was just dangling there. I checked the fuses in the interior passenger side and also the wire fuses by the battery and they all look good. From what it looks like maybe I don't have a pressure switch.

[sblake01]

That's not a factory system. It likely doesn't have a pressure switch as many add on systems didn't back then.

[NewGuy146]

It looks like I'm missing something in between the control know in the console and the Compressor since those wires are loose. Any ideas before I haul this off to a A/C repair shop?

[NewGuy146]

I took the Z to a recommended A/C shop and they couldn't get the A/C to run. They were unable to get the power to the compressor. They tested the compressor and the pressure switch and they tested fine. I've done some digging and believe my A/C system is a dealer/port install. Below is a picture of the system. The A/C is controlled by a knob in the console and the Vent/Heater controls the fan. I believe it is an A.R.A system.

Does anyone have a wiring diagram for that type of system or some ideas to try?

It's getting hotter day by day and I'm not sure I will survive in a car without A/C

[sblake01]

On the back of that knob/switch there should be two wires, one that feeds power to the switch and another that sends power for it to the compressor. There's also a capillary tube that goes from the back of that switch to the evaporator core to sense it's temperature. Check to see of you have power to the wire that feeds the switch when the key is in the on position and your HVAC controls are in the position show in your attachment. If so, try jumping the two wires together and see of the comperssor comes on. That would tell you whether or not the switch is bad.

Edited May 21, 2012 by sblake01