OK I have a new compresser & clutch. freon is right on using gauges. Ac controler contacts cleaned & working. AC works great in the garage, BUT when I give it to the Wife itworks for a couple of miles and shuts down. At that time the controler lights flash and it throws a 09 code in the 00 setting. When it is throwing the 09 code there is no power to either side of the low pressure switch. If I disconect the battery wait 10 min. everything goes back to blowing cold air. Any ideas?

 

PCM monitors opening and closing of the Low Pressure Switch and Pressure rise from the Pressure Sensor to determine if there is a low charge condition. I'd suspect that the Low Pressure switch is intermittent. Often it's the switch, but take a good look at the Connector. Try wriggling it around to see if it will duplicate the code. It could also be losing the Pressure sensor signal, so you might just make sure there's a good connection there, though an open or shorted to ground Pressure Sensor signal should also generate a engine trouble code - something in the 70's for an OB1.

 

there are two switches in the lower line going onto the evap. and there is one in the upper line. Do you know what each one is? my helms FSM is at home

 

Low Pressure is on the Outlet/Suction or larger line and has 2 wires which is simply connected/or spliced inline with the ground or driven side of the Compressor Relay. Pressure Sensor is on the Inlet/Liquid or smaller line from the Condensor and has 3 wires - PCM reference (5 volts), ground and PCM return. It's like a thermistor and the signal or voltage return rises with pressure with each volt being approximately 100 psi. PCM recognizes a static pressure in the area 80 psi or .8 volts as being normal, but whatever the signal, it's programmed to look for the pressure or voltage return to rise when the compressor engages. Best to monitor what it's doing with a Scanner, but your problem sounds like an intermittent at the Low Pressure Switch.

 

Thank you very much. After you posted this I told the four seasons (B&W) tech. what you said , he then asked me if I had changed the factory low pressure switch out for the one needed when you convert to the new style freon. I had not and now have ordered the proper low pressure switch.

 

If there's a screw between the terminals of the stock switch, it's adjustable and I'd check any switch that you install for proper calibration. Hook up you gages and monitor the low side. With the a/c on max, disconnect the blower motor and when the air flow ceases, low side pressure will drop. For R134 (the new stuff), the switch contacts should open at 22.5 psi and the compressor should shut off. For R12 (the old stuff), the threshold is 25 psi. Assuming there's a screw between the switch terminals, you adjust the threshhold by turning it counter clockwise to lower it; clockwise to raise it. 1/2 to 1 complete turn is a good place to start if it isn't right (engine off). Then plug the blower motor back in. Restart it and let it run for a few minutes on max to restablize it and then disconnect the blower motor again to see where it is. Adjustments usually take a few trys.

Seriously doubt that the cutoff threshold has anything to do with the low gas code - assuming it's clean and fully charged. All the PCM is looking for is a rapid cycling of the switch contacts. A fully charged system rarely sees a low side of 25 or 22.5 psi (and if it's 70 degrees or better at the Condensor, it won't drop this low). Stock specs are no more than 8 cyles per minute and at lower ambients, the contacts simply open and remain open for a considerable amount of time - they shouldn't exceed the stock threshold of 8 cycles, or if they do, it's because the orifice is clogged up with junk.

 

SunCr --- Thank you.