How do you know if the two electric fans under the grille are running at the correct speed? With AC on, both run, and can be heard above the rest of the noise from this mobile tea kettle. If they were "slow" that could cause AC air flow problems at idle, which goes away at speed. Can I rule them out as the problem by having the truck idle, and manually turning AC compressor on/off while watching AC guages and thermometer stuck in the center duct? Would this procedure be a good test for expansion valve or compressor problems?

 

I think problem is compressor or expansion valve or both. Here is results of today's tests under the shade tree:

90 degrees ambient, coolant 183 after 15 min idle at 700 rpm, no AC on.
Battery volts 14.0, switch on AC with interior fan at max - 13.81 volts
Also switch on head lights - 13.74 volts - so alternator is charging battery even at idle. Metered wire to fans for condenser - 13.05 volts. Put plastic soda straw into operating fan blades - each fan shredded the straw. So fans seem OK.

Set up large 120 volt fan to blow into front grille. At idle without AC it dropped coolant from 183 to 178. With AC, no change from previous stated problem of rising coolant temp.

Here a AC guage readings:

700 rpm (idle) - 70 low / 435 high - high limit switch kills compressor, pressure drops to 325 - 350, compressor comes back on, cycle repeats. Warm air, low side line to compressor warm to touch.

1500 rpm - 50 low, 405 high, vehicle cools off, center duct at 44 degrees

2500 rpm - 40 low, 295 high, vehicle cools slightly more

Thinking slight overcharge, I removed some refrigerant. Low side in the 35 range, high side starts around 250, then slowly crawls up to above 350, cooling declines, coolant temp heads up to 221. Turn off AC and it will drop back to 178- 183.

Thinking this may be a compressor that just can't do the job at idle. Or is it a bad expansion valve that is sticking? If expansion valve, why would it work OK at 1500 rpm and up?

 

Previous owner made splice near top of radiator and reversed fans. So they subtracted air flow instead of increasing it (making water radiator hotter) and made condenser appear to have fins blocked with mud (no air flow). Put fans right and success. Made a new thread about it.

THANKS!

 

Awesome! Nice catch.