1992-95 OBD1 LT1 computers need a number of inputs to permit/activate the A/C clutch relay output. You'll need:
-A 3-wire A/C pressure sensor mounted on the hi-side line
-A 3-wire A/C Evaporator Temperature Sensor Module with remote (wired) sensor probe mounted in the evaporator core itself
-An A/C Clutch status wire (just tie into the green wire that goes to the A/C clutch)
-An A/C Request Signal (from the Fiero HVAC control panel)
(The LT1 PCM controls the A/C clutch relay much like how the stock Fiero system works.)
The A/C Evap Temp Sensor module is a small box with 3 wires going in and 2 coming out mounted inside the donor LT1 car behind the glove box and you should be able to get to it quite easily (at least in F and B body applications). What you can't easily get to is the actual sensor probe which is attached to this small module via the 2 wires because the temp probe itself installs into the evaporator core, which is buried in the HVAC housing. What I have done in the past was just cut the remote probe wires so I could get this "module" out of the donor car. Then I've wired up a standard GM intake air temp sensor to this module and installed the temp sensor into the evaporator box in the engine compartment (or in the case of the Fiero, it would be in the front trunk compartment). When I've done this, the PCM enabled A/C operation and didn't have much issue with me using an IAT sensor as the temp probe for the A/C evaporator temperature module.
[This message has been edited by Darth Fiero (edited 08-09-2013).]