Rough running or low idle speed when air conditioner is operating.
The air conditioner (a/c) takes a fair bit of horsepower from the engine. A Fast Idle Control (FICD) solenoid allows vacuum pressure to operate an actuator (FIA) that increases the idle speed of the engine to compensate when the a/c kicks in.
There is a small rubber vacuum hose from the inlet manifold to the FICD (first picture) which is mounted above the brake booster. The FICD is supplied 12 volts via an Orange wire with a blue or purple stripe. Its negative is a black wire.
Another hose runs from the FICD to the FIA diaphragm (second picture) which is mounted near the front of the carby. Check the hose for splits or holes if the engine runs rough when the a/c cuts in.
When the a/c cuts in you should be able to see the FIA rod push on the carby linkage. If it doen't operate, you may need to use a hand vacuum pump to check that the diaphragm rubber isn't split or holed.
Another possibility is that the FIA operates, and the revs will rise, but the engine runs rough. If this happens the diaphragm rubber may have a small hole or split. This will become apparent when you use the vacuum pump and the actuator operates but returns to its normal position while it is still connected.
The FICD is powered by the air conditioner relay on a vehicle with a manual transmission.
A vehicle with an automatic transmission also has additional protection control via a Thermo Switch which operates an a/c cut relay, connected in series with the a/c relay.
Cooling for an automatic transmission is achieved by pumping its fluid through a core inside the radiator.
The Thermo Switch is situated on the radiator and it should have a blue and Yellow/blue wire. It operates when the engine coolant reaches 107 degrees C to cut out the a/c and off to allow the a/c to operate when the temp drops below 103 degrees C.
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