| This year after fixing a burnt injector and doing the 60K service I decided to tackle the a/c system in my 1994TT. I have learned a few things: 1. The a/c system in the Z is NOT a clutch cycling system. The temperature in the evaporator is SOLELY controlled by the expansion valve, by way of an oil filled tube and bypass plumbing. When the evap oulet temp approaches 38F the expanding refrigerant is rerouted directly to the compressor. 2. The ground for the electromagnetic coil that operates the a/c clutch is provided by the ECU. 3. Two fail safe circuits that interrupt power to the comptressor's electromagnet are incorporated into the a/c system for protection. One is the dual pressure switch, which "monitors" refrigerant level. If system pressure gets too low or too high and the switch opens up cutting the ground to the a/c relay. The other is called the Thermo Control Amplifier. This monitors evap temp and if it gets below 38 will provide a 12VDC signal to the ECU which in turn disconnects the ground to the clutch magnet. The a/c in my car works well, but just for one or 2 minutes when for no apparent reason it quits cooling. A minute later it cools again and thus lives in a clutch cycling mode. During my testing I bypassed the dual pressure switch and relay, powering the clutch directly from the battery. NO CHANGE. clutch still cycles. This suggests that it is the ECU that is causing the cycling via the TCA. The possibility exists that the expansion valve has failed and the TCA is doing its job but the discharge air is never that cold so my guess is that the TCA is malfunctoining. Since this device provies a 12 volt signal (when it thinks the evap is too cold) disconnecting it would prevent the ECU from responding by cutting the ground. Is there a source for the pinouts of the ECU connector? I did no see them in the FSM. I know the TCA is in the air box next to the evap but getting to it is another matter. I thought I would push its wire off from the ECU connector for testing. Any help or ideas would be appreciated. PS I filled the a/c with R134a till the gauges reached the specified values for 88F according to the FSM.
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