bumb...
i found this...of another topic..
"Given you just had work done done on the car I'd say the ambient sensor is unpluged ( it should be the little black lump next to the horns, behind front bumper).
Like GTScotT said its a common thing, mechanic forgets sensor, A/C thinks the outside temp is -40C or something and fires up the heater 4 ya
There are 2 other sensors, one at the back of the dash ,left side (sunLoad) and one just to the left of the steering columb (interior temp).
Any of these left unpluged/faulty will screw up ya AirCon (usually with the heat your gettn) "
"have a search on SAU for heater threads you should find plenty of info on the heater. being a 33 owner I'm not familiar with the 34 BUT if ya stick ya head under the glove box and hit the 'recircualte air' button, you should see a 'rod and lever' arangement mo0ving, thats the cowl door. Same goes 4 the heater cores tap, change the temp and something will move to direct the water flow.
like I said though do a search. I'm sure I've seen full removal guides and all. "