I have been having with my A/C being a little cool and then getting hotter and hotter. We have Freon in the A/C system and the clip in the air box lid is in tack. I have the electronic control system. I was wandering what the A.T.C.(temp. control module or also called Power module relay) do? This piece is bolted with 3 seven millimeter screws on top of the evaporator core housing and has two plug in's. I was wondering if this could cause my A/C to get hot out of the vents if it is bad. Any knowledge of this piece would be grateful.

 

I have an 88 coupe w/ electronic temperature control also:

On the top of the evaporator are 2 connectors, this is the Blower control module. it is solid state, it receives input from the electronic control (.5 to 5 volts), and varies the supply to the blower from 4 volts to 12 volts to change the blower speed. (12 volts is max speed). The symptoms yyou describe lead me o believe this is not your problem (fan is running, and speed changes to demand--right?)

1) the in car temperature sensor, is located just above the drivers head (slots in plastic). Thi feeds to the "electronic module" to adjust temp accordingly.
2) the compressor cycles on the pressure cycling switch, turns off on low freon pressure (lo freon charge or not enough heat load). This is the "switch" on top of the evaporator. (compressor off @ 25#, on @ 47#)
3) On the return line to the evaporator are 2 switches, one opens on "hi pressure" to tell the ECM the AC is on so it starts a fan, the other trips the compressor on excessively hi pressure (indicates the condenser has lost cooling).


4) you can perform an electronic diagnostic test: I start w/ the engine running A?C in auto, temp set to 65...
press and hold the rear defog button, then momentarily press the manual fan up button. the display should show -01
If this doesn't work then press and hold the ext temp button and momentarily depress the auto fan speed button the display should show -01.

with -01 showing you are in the diagnostic mode, press the warm button to advance to -08
press the cool button.

here are the error codes listed in the manual:
oo program number (mine displays this, the A/C works fine???)
01 feedback potentiometer open
02 Ambient sensor open
04 Ambient sensor shorted
08 In-car sensor open
16 In-car sensor shorted

it further states other numbers are displayed more than 1 problem is detected

good luck, I'll look in if you have more to ask.