Temperature fluctuation in a/c mode

my son has a 2001 isuzu rodeo sport with a 3.2liter v-6 engine. recently he has noticed a marked increase in coolant temp when idling with the a/c on. a recent fan clutch replacement did nothing to resolve the problem. same result with a coolant system flush and coolant replacement. upon accelerating to 1400 rpm or better, the temp goes back down to normal range. the radiator and a/c evaporator are free of debris. any ideas? thanks

Radiator fan and worn water pump would be at the top of my list.

Have you explored the possibility of high AC pressures,perhaps a recent AC charge was really a over charge.

I lean more towards poor performence from the radiator.

  1. Does this vehicle have an electric fan in front of the radiator that is supposed to come on when the A/C comes on, or when water temp hits a certain point, or when condenser pressure gets too high or some combination of conditions? Is it coming on? If you have no such electric fan, does the new fan clutch seem to connect fully when the car is warm? (turn off car and try to spin fan, should turn a little, but much stiffer than when car is cold)

  2. Next suspect, water pump has eroded blades and inadequate flow at low RPM.

  3. Radiator flush did not clear obstruction. Can you touch the whole back of the radiator with your hand? Is it uniformly hot all over?