A/C overheats engine?

reno · Jun 5, 2008

What would make my A/C periodically overheat (temp rises WAY up) my engine? Sometimes the A/C will not blow very cold and the temp rises and rises, I turn off the A/C when the temp gets around the "A" in Normal. If I turn it back on (A/C) and use the water hose and blast the condenser, usually it blows ice cold again. Temps here have been in the upper 90's and humidity has been high.

I have a theory on what the prob is, but am hoping it is not that, will be a very EXPENSIVE repair that won't get done for quite some time.

Thanks
-=Reno=-

MAKG · Jun 5, 2008

Take a look at what the pressures are doing. I suspect it's overcharged.

Bob Ayers · Jun 5, 2008

I suspect it's your fan clutch going bad. Unless there is something else causing the engine to overheat: Blocked radiator, thermostat, or air bubble in the system. If the ECT sensor detects that the engine is too hot, the PCM will shut the AC compressor down.

reno · Jun 6, 2008

I will hook up the manifold guages this afternoon and report the readings.

Bob Ayers,water pump and fan clutch was changed about a month before I bought truck (still have the reciept from PO).

MAKG · Jun 6, 2008

It's possible for almost any new part to be DOA. New does not mean good.

However, if it were the fan clutch, issues would show up at idle or very low speed only.

reno · Jun 6, 2008

Makg, you are right. Truck never runs hot. I have let idle for 15 minutes when I flushed the system and never went past the O in Normal, and this was in 92 degree weather. This started when I decided to run the A/C the other day. The P.O. fixed the A/C, but that does not mean correctly. It is possible it is overcharged (I hope so), I was beginning to think blockage, possibly at the orfice tube.

reno · Jun 7, 2008

Makg, I would say you were right. 175PSI High 175-180PSI Low. Engine Off. Well now back outside to do some draining......

Bob Ayers · Jun 7, 2008

reno said:
Makg, I would say you were right. 175PSI High 175-180PSI Low. Engine Off. Well now back outside to do some draining......

NOOOOOOOOOOOO!!!! You have to check the pressures with the engine running! The low and high side pressures will equalize without it running.

reno · Jun 7, 2008

Already done Bob,but I believe i have blockage.

A/c ON MAX, @ Idle ~800rpm, Low=50psi and High=300psi, after 5 min Low=42psi and High=280psi. Vent Temp went from 80 degrees to 68degrees, then brought idle upto 1000rpm for 3min, vent temp dropped to 62degrees.

Now I noticed when I rev up the engine the High side keeps going up!! I got to 400psi with no problem. Low side hardly moved (dropped about 3 -5 psi 42-40psi). I drove the truck down the road at 30 mph, A/C on max, drove about 10 blocks total, temp dropped to 57degrees, but compressor seemed to pull a LOT of H.P. from the engine.

MAKG · Jun 7, 2008

Without knowing the ambient temperature, I can't say for sure, but those sound like very high pressures.

Unless it's hot as all heck. 175 PSI static corresponds to over 120 deg (underhood!).

Note you will also get anomalous high pressures from water contamination.

reno · Jun 7, 2008

Ambient outside air was about 94 - 96 and was possibly WAY past that under the hood. Believe me I felt every bit of that heat!!

High Head Pressure I believe is an indicator of blockage, right?

MAKG · Jun 7, 2008

You have high head pressure AND high evaporator pressure.

Extreme heat, or overcharging.

reno · Jun 7, 2008

I filled the system back up (I drained to much and clutch was cycling like crazy!! on for 10 secs, off for 15, then on, then off....), but anyways, filled to 30 psi Low side and clutch was cycling correctly. Then I used my old gauge I still had before I bought the Manifold gauges, the old one has a "Color chart" on it. Blue=filled, yellow=alert and red=danger. It was in the middle of the Blue. But I notice after letting the truck idle for 15 - 20 min, it climbed, so that is when I hooked up the low side of the manifold gauges and got these readings, I would guess it is still in error on my behalf to have a slight to much charge, I used almost a full can of R-134a, more like a little over 3/4ths. It blows cold, not freezing cold like my kids car or the wifes van, but cold, ~57 - 62 degrees in 94 - 98 Temps (Ambient). I think I am going to change that thermostat (if thier is one :dunno:

) and Radiator cap. No pressure relief came from the cap when I lifted the release, and coolant rushed out, and did not seem to be circulating like it should. Temp gauge was showing no sign of high heat either.

DesertStorm · Jun 7, 2008

MAKG said:
You have high head pressure AND high evaporator pressure.

Extreme heat, or overcharging.

R-134a will usually run around a 40# suction when the interior of the truck is very hot. He needs to check his super heat and sub cooling to determine if it is overcharged or has a restriction. If sub cooling is very high it has a restriction. If sub cooling is low it is overcharged or does not have enough airflow over the condenser. In 90+ deg ambient conditions a normal subcooling would be 10-15 deg. If it is much over 20 i would start to look for a restriction. As for discharge pressue 134a should be about 200 max. after that you will start damaging valves in the compressor. 280 is waaayyy to high. Superheat will be around 18 to 20 deg when cab is warm and drop to around 10 to 12 when cab is cold. Direct Orfice Expansion systems do not respond rapidly when under a heavy load condition.

AND-- if non condensables aka air is in the system the same problems will occur. If a proper vaccum was not pulled on the system air will be in the system and cause extreme problems/damage. And as for the compressor pulling alot of HP it is overheating and trying to lock up thus the feeling of it pulling more power than required. The compressor oil does not like to be too hot. The cool suction gas cools the oil and the bearings.

reno · Jun 8, 2008

What is "Super Heat" and "Sub-Cooling"?

I was looking up parts in a online junkyard parts lookup for some approx prices, what is the difference between a integral compressor and a hang-on?

A/C overheats engine?

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