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Very strange problem with A/C.
While sitting still (engine running of course) the A/C will run as it's supposed to. Regardless of RPM (Except at WOT) the compressor stays engaged and the coolant fan runs.
When I drive the car, however, the A/C compressor is shut off after a very short drive. (Maybe .3 miles) It will not come back on unless I shut off the car (ignition to OFF) then start the car again. This is repeatable.
Even more interesting is that if you cycle the A/C manualy, it will run as long as you want it too, so long as you cycle it every 15 seconds or so. So while driving: turn on A/C, count to 10 and turn to off, count to 5 and turn to MAX A/C... You can do this forever and it will always come back on.
Monitoring the A/C clutch relay reveals that the signal from the computer is disengaging the clutch. That lead me to a sensor problem so I started monitoring those. I first checked the reference voltage from the PCM which is supposed to be +5 volts. It's at 5.04 volts rock solid.
As far as I know there are only two sensors in the system; the evaporator temperature sensor and the coolant pressure sensor. I've monitored the voltages of these sensors while sitting and driving.
The evap. sensor ranges from 1.2 to 1.4 volts depending on heater fan setting whether sitting or driving.
The coolant sensor ranges from 1.6 to 2.0 volts depending on engine RPM while sitting. The voltage varies between 1.8 and 2.2 volts while driving. I thought this was the most likely cause, except that the compressor doesn't shut off at the high point of this sensor's voltage range. It has shut off at several voltages within this range.
To eliminate these sensors as the cause, I chose a value in the middle of these voltage ranges and held that voltage constant. (with a variable resistor) I got the same result by holding constant either sensor.
So with pressures normal, sensor inputs normal and everything mechanically sound... WHAT AM I MISSING?
Is the computer monitoring a sensor I've not discovered? Does the operation of the A/C require some other input that isn't being met?
Please help me...
While sitting still (engine running of course) the A/C will run as it's supposed to. Regardless of RPM (Except at WOT) the compressor stays engaged and the coolant fan runs.
When I drive the car, however, the A/C compressor is shut off after a very short drive. (Maybe .3 miles) It will not come back on unless I shut off the car (ignition to OFF) then start the car again. This is repeatable.
Even more interesting is that if you cycle the A/C manualy, it will run as long as you want it too, so long as you cycle it every 15 seconds or so. So while driving: turn on A/C, count to 10 and turn to off, count to 5 and turn to MAX A/C... You can do this forever and it will always come back on.
Monitoring the A/C clutch relay reveals that the signal from the computer is disengaging the clutch. That lead me to a sensor problem so I started monitoring those. I first checked the reference voltage from the PCM which is supposed to be +5 volts. It's at 5.04 volts rock solid.
As far as I know there are only two sensors in the system; the evaporator temperature sensor and the coolant pressure sensor. I've monitored the voltages of these sensors while sitting and driving.
The evap. sensor ranges from 1.2 to 1.4 volts depending on heater fan setting whether sitting or driving.
The coolant sensor ranges from 1.6 to 2.0 volts depending on engine RPM while sitting. The voltage varies between 1.8 and 2.2 volts while driving. I thought this was the most likely cause, except that the compressor doesn't shut off at the high point of this sensor's voltage range. It has shut off at several voltages within this range.
To eliminate these sensors as the cause, I chose a value in the middle of these voltage ranges and held that voltage constant. (with a variable resistor) I got the same result by holding constant either sensor.
So with pressures normal, sensor inputs normal and everything mechanically sound... WHAT AM I MISSING?
Is the computer monitoring a sensor I've not discovered? Does the operation of the A/C require some other input that isn't being met?
Please help me...
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