The air conditioning on this vehichle worked fine and then, after a
> winter of disuse, whenever I put the heater switch to A/C either High,
> Normal or Econo mode , the fuse blows in the fuse block. The heater
> blower motor works fine in "vent" and "heater" mode. The fuse also
> blows if I put the heater switch in defrost mode (windshield) but only
> if I slide it all the way to the extreme right (defrost+engine fan).
Sounds like the compressor is drawing too much current,it may be seized or close to it.The reason the fuse blows also when you put it on defrost is because the compressor is used when in that mode.
> The problem seems to be linked to the radiator electric fan motor
> since when the heater fuse blows, the raditor fan stops working. I've
> learned this the hard way of having the engine overheat once on my way
> to work. I have changed 1 or two of the fan control relays in the > vehicle.
Another reason why it leads me to believe it may be a compressor problem.The fan comes on when the compressor engages.If the compressor does not work,the fan will not come on either when you put it in the a/c or defrost mode.As for the fan going out completely to cause you to over heat I think the 2 circuits may some how share the same fuse.Im not sure and am surely not an expert on the subject,but it would be worth it to have the compressor checked out.Especially if it is the original compressor.
> Anyways, any suggestions are greatly appreciated. I'm a tinkerer and
> don't justify bringing it in to an A/C shop to have them stiff me with
> a huge bill for a 1990 cavalier.. I have Haynes and Chilton manuals > for this car.
No need for them to give you a huge bill.Ask them how much a diagnostic charge is.If its like 40 bucks tops,then it may be worth your while to pay it and then do the work yourself.Let us know how you make out.