The latest from my local mechanic on the ac problems of my 95 is that he suspects ac programmer wacky. The ac rarely immediately comes on after the car has sat for the day or overnight but once the compressor finally kicks in, the air is wonderfully cold. The delay seems to be anywhere from a couple of minutes to 10 minutes. Once the system is finally on everything seems okay but before struggling with the ac programmer (which I cannot even get to without being double-jointed), can a dummy like me easily check the refrigerant charge by buying some kit in Pep Boys or Autozone?

The charging instructions in the GM Service Manual make it sound daunting (e.g., the system should be evacuated before recharging, etc.) However, I keep seeing these simple kits advertised--are they safe and reletively foolproof?

Thanks,

Doug

 

If it's blowing cold and the compressor isn't cycling, the charge is probably ok (and the '95 will shutdown and spit out a trouble code if it isn't). Otherwise, you need a manifold gage set - about $80 to see what the charge is. You can also use a scanner which will give you the high side pressure from the pressure switch, but I doubt charge has anything to do with it.

Here's how the '95 works - A/C request travels over a serial data line from the Dash Controls to the Programmer. Programmer sends the signal onto the PCM which then drives (grounds) the compressor relay as long as the pressure switch signal (on the high side line) is somewhere around .8 volts (which is about 80 psi and with it sitting still and fully charged, it should have that #). Compressor will engage as long as the low pressure switch contacts are closed and that switch closes at 50 psi (again it should have that). You could just try a new relay, but I'd troubleshoot first by checking the low pressure switch - put a meter across it and verify continuity with the engine up to temp. Then, with that verified and a/c requested, I'd wriggle around that connector and maybe even remove it and plug it back in to see if the clutch engages. If the contacts read open - replace the switch. And if monkeying with the connector gets it to work, you'll probably need a new switch and a connector. If all that checks out, a bi-directional scanner will emulate the control panel and send specific control panel requests to the Programmer. If it all works, the data lines can be ohmed out, but it's more probable that the Dash Controls are on the fritz. If the scanner generates the same response, you may need a new Programmer, but I would also want to see whether or not there's a "Yes" on the Scanner Display when you request a/c and the voltage signal and pressure readout from the Pressure Switch to rule out the PCM. If you mechanic doesn't have the right scanner, I'd see what a dealer wants to hook one up - can't imagine that it's more than an hour for diagnostics.

 

Thanks for the info but I don't have scanners handy so I would probably try the dealer for a diagnosis. I found two connectors under the hood on the passenger side. Both go to fittings on what I believe are ac lines--one of the connectors is physically higher than the other and they are on different lines. The uppermost connector has a dark blue wire and a green wire--the lower one has two or three wires (I forget). I'm not sure what these are (high pressure sensor? low pressure sensor?) but I jiggled these to see if anything would happen and this did not have any effect.

My local guy (not a gm dealer) said the type of behavior I was experiencing was a frequent problem for this ac system (and typical of an ac programmer problem) and he suggested that using the ac more would help (I rarely use the ac and it probably had been on only once or twice over the last 9 months until the latest heat wave here).

 

The 3 wire switch is the Pressure Switch. 5 volt reference from the PCM, Return voltage back to the PCM and a ground. Voltage rises with pressure.

Running it has nothing to do with it - though using it every now and then does prolong the life of the shaft seal which is somewhat problematic on the Nippondenso compressor. I'm pretty sure your problem has to do with electrons. A scan will tell you a lot and I can't imagine it costing more than 85 Bucks - assuming shop labor is similar to what it is in San Diego.