I am trying to trouble shoot my AC and early in the diagnostic, maybe the first thing, is to hook up the Tech1 and see if the compressor clutch is turned on. Well I do not have a Tech1 and am not sure I want to spend as much as they seem to be selling for. Is there another way to check and see if the output is turned on? I am planning on scan and tune software before too long. Is there some good scan software I could use in the place of Tech1 and kill 2 birds with 1 stone?

 

You can use Datamaster which is available here for download:

www.ttspowersystems.com

You also need an interface cable available here:

www.akmcables.com

You can use the software for 20x before having to pay for it. It will show you the status of the AC compressor.

 

Nice but not always necessary. And see if the low pressure switch contacts are closed first. It takes 50 psi to close them which doesn't take a whole lot of gas. The clutch won't engage if they're open (too cold or the gas is gone) or if the connection is bad. If they are closed, make sure the connection at the switch is good - wriggle it around - hold the connector on the switch. If that gets it running, get a new connector or switch. If it doesn't, make sure it doesn't have the low gas code in memory - disconnect and reconnect the battery. If it then starts and stops, it's probably out of gas. Get your scanner for other things. Buy a manifold gage set to help you rebuild the a/c.

 

Manifold gauges are a must for AC work, also you can disconnect the clutch connector and probe it for power. You do not need the Tech 1 for AC repair.

 

Sounds like just what I was looking for. Thanks

I am sure it is low on gas, this all started with a high pressure sensor leaking. I replaced the sensor but now cannot get it to take a charge because the compressor will not come on. The can of Freon I got has a gauge on it but not one of those ones that has a gauge for high and low side pressure will I need one of those just to charge it if I can get the thing running?

I thought about this but for some reason I thought the connector was a 3 pin, not sure about that now though. Is it voltage high clutch engaged, low disengaged?

 

The switch you replaced is the Pressure Sensor and is used for fan control, condition of charge and high pressure shutdown. It's a thermistor with a 5 volt reference from the PCM. The signal back to the ECM rises with pressure with each return volt being about 100 psi. The third wire is ground. The PCM usually likes to see about 80 psi or .8 volts static pressure before grounding the Relay, but more importantly, it looks for a voltage or pressure rise - as it should - once the compressor engages. If not, it shuts down and on some models sets a code. A high pressure shutdown occurs if the voltage rises to 4 or greater or 400 psi. If the reference is shorted to the return signal, you can get that, so make sure the wiring isn't nicked and that the connector is in good shape.

The low pressure switch - on the Evaporator or big line - is also monitored by the PCM - through the clutch relay - to determine if the charge is ok. All it does is see if the Relay is opening and closing rapidly and if it is, the PCM interprets that as low gas, so you get the code, and it shuts off.

To recharge, you clear the code and to keep it from resetting, jumper the low pressure switch connector with a paper clip (ie, you make sure it's a completed circuit). Hopefully you've got some gas in it and you can see if it does by ohming out the Low Pressure Switch contacts. As I said earlier, it doesn't take a whole lot to close them - but if you clear the code and start it up with an insufficient charge, it will cycle too much and the PCM shuts it back down.

Hope you got the right gas. '93 was R12 from the Factory and the only cans I've seen with a pressure gage are R134. Be sure - don't mix the two. And, since you swapped out the Pressure Sensor, start by disconnecting and reconnecting the battery first and then seeing what happens. Disconnecting that harness may have fooled the PCM into thinking there's a problem and clearing everything out of memory may get it running again.

 

I will have to check the low pressure switch and see what is going on there. I have disconnected the battery several times but not latly because I do not get any codes from the ECM or the Climate control and it acts like it thinks everything is fine. The LED does not flash and it blows air like nobodys buisness out of the selected vents its just always hot air. I had the system converted to R134 last year when the evaporator I think it is was, was replaced.

 

I got the A/C working and wanted to post thanks to everyone that helped and the solution in case it could help someone else. I got the Datamaster and cable to go with it and using the free preview scans looked to see what was going on. The A/C pressure was running 28.1psi the FSM said the clutch will not engage if it below 44psi. So I jumped from the battery to the A/C clutch and started dumping Freon in until Datamaster said I had 75psi while not pumping and the clutch unjumped. Then I could fill it normally, just had to unhook the battery a couple times cause it kept erroring out for low Freon. Now it blows nice and cool, just in time for some really hot days here. I just hope this is the last of the leaks I think it is. It was a slow leak last summer and the high pressure sensor was leaking for sure. Well thank you for the help with my first A/C repair.