Engine Overheats while using A\C

[hellraiser_88]

One of my friends just bought a 1993 s-10 with a 2.8 5 speed and seem to have a cooling problem. The thing is it only overheats when the A\C is on. We've flushed the cooling system 8 times but keep geting rusty water. When we flush it out at first the water is clear, but two days later it's rusty again. The water pump, thermostat, heater core, and hose have been replaced. When the pump was off my friend flushed the motor out with a high pressure hose and that flushed most of the crap out. We're both stumped.

[Sparky2263]

When diagnosing overheating problems, you need to think in terms of removing heat. The cooling system on his truck is capable of removing the heat the engine is producing, but, when the added heat of the condenser is put in front of the radiator, it can't remove enough heat.

I'm wondering if the fan clutch is acheiving lock-up when the thermal element expands. I'm also wondering if the radiator has so much gunk in it, it's lost it's ability to convey heat to the air flowing over it. Also, is the fan shroud in place and situated properly?

[THA_BAD_ONE-0]

yea my clutch fan went bad and my 2.5l it ran hot with ac on

[T Man]

I see the rust as the problem. I think you are just getting by with the AC off, but when it is on, the rad, which is probably full of rust deposits cant do its job. Back flushing it helps, but the heat that builds up is a much better solvent and removes it, thereby giving you your rusty coolant a few days later. Just my .02