Nissan Repair: 1990 Nissan 240SX A/C Problems, 1990 nissan 240sx, nissan 240sx

Question
I have a 90 Nissan 240SX that for the last couple of years has been having intermitten AC issues.  It'll randomly start blowing hot air and then start cold again.  It started to be more noticeable over the last few months as it would get  hotter when I was stopped then become cold again as soon as I was moving.  The problem was that as soon as I stopped the car, the water in the reserve tank was boiling.  And then it progressed to boiling and filling up the reserve tank and letting off steam and finally overflowing.  At this point the temperature gauge would read really hot (just under the white 'H').  Had a mechanic look at it and he found that the AC fan wasn't working at all.  But couldn't figure out which of the sensors was causing this.  He changed the thermostat, the cap, flushed the radiator and then provided me with a temporary fix - he wired the AC fan directly with a fuse...when I turn on the AC, the fan would kick in immediately.  Seemed fine for a few days, but now its back up to its old tricks.  The temperature gauge stays within what it's always been a line and half above center.  But the car is back to having the water in the reserve tank boiling and steaming and spilling over.  Any thoughts?  I may need to take it to a dealer to get this looked at and am afraid this might be an expensive fix.

Thanks

Answer
Joe,

The airconditioner turns on the auxillary fan when the compressor is on via a relay.  I would change the relay.  If he hard wired the fan to the compressor I would think the fuse has blown since there is too much of a load on one circuit.  The overheat problem is not a problem when the airconditioner is off?  If this is the case you have found the problem on your car.  If not I would have the cooling system checked for exhaust gas to see if the head gasket has blown.  This car is known for this problem and I have replaced several.  So, first I would check the fan for the airconditioner and see if it works when the airconditioning is turned on and if it is not working go to the first steps.  In either case replacec the relay and wire the fan up properly.  Also, be sure to check the radiator to see if it is plugged and needs to be recored or replaced.  I like to go with more substantial radiators when I replace them to give better cooling.