View Full Version : A/C overheats engine?
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=-
Take a look at what the pressures are doing. I suspect it's overcharged.
Bob Ayers
06-05-2008, 06:13 PM
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.
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).
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.
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.
Makg, I would say you were right. 175PSI High 175-180PSI Low. Engine Off. Well now back outside to do some draining......
Bob Ayers
06-07-2008, 12:36 PM
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.
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.
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.
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?
You have high head pressure AND high evaporator pressure.
Extreme heat, or overcharging.
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
06-07-2008, 11:48 PM
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.
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?
How much R-134a is normally needed to fill a system in a 93 Ranger that once was R-12? 2 12oz cans?
The rule of thumb is 80% of R-12 capacity. The R-12 capacity is on the blower housing label. It's usually close to 2 cans.
Soooo, if the R-12 system takes 2 cans which is 2 12oz cans which = 24 oz or 1.5 lbs, then R-134a would be about 1.5 cans or ~19oz?
Don't guess at capacity. You'll make a POS.
READ your label. Fill it to 80% capacity with R-134a (after cleanup, repair, etc.).
DesertStorm
06-09-2008, 10:01 PM
Don't guess at capacity. You'll make a POS.
READ your label. Fill it to 80% capacity with R-134a (after cleanup, repair, etc.).
Yes 80% capacity is correct. But you do not have to get the scales and slide rulers out. Charge as liquid only and slowly fill it up. Watch the suction pressure. At around 32-35# it will stop pulling down and shutting off on the LPS. Charge it a little more. 38-42# depending on temp/load. Put a temp. probe in the vent. Charge only on MAX AC with fan on high. temp out of vents will get to around 40-44 deg. F. Bring rpms up to about 2000-2500 pressures will drop back down to the lower 30's. Should be really close.
Bob Ayers
06-10-2008, 05:30 AM
Yes 80% capacity is correct. But you do not have to get the scales and slide rulers out. Charge as liquid only and slowly fill it up. Watch the suction pressure. At around 32-35# it will stop pulling down and shutting off on the LPS. Charge it a little more. 38-42# depending on temp/load. Put a temp. probe in the vent. Charge only on MAX AC with fan on high. temp out of vents will get to around 40-44 deg. F. Bring rpms up to about 2000-2500 pressures will drop back down to the lower 30's. Should be really close.
Be very careful liquid charging that you don't slug the compressor.
Well now see, that is what I did. I drained the A/C down to where the clutch would cut in and out rapidly. Then I hooked up my can of R-134a and began filling. Low side was around 18 - 20psi. Filled till low side had a reading of around 32psi. I checked my temp in cab, in center vent, a/c on max, fan on high, it read 78F. Brought rpm's up to 1000 then 1500, no change in temp. It was about 94F outside, I was in the shade, about 90F. Low side dropped to about 28psi. So I started filling again, till gauge showed 32psi, temp dropped to 62F, brought rpm's up to 1500, temp went to 60F. When I went back out to the gauges and revved the engine (do not know what RPM) high side would keep increasing, and let off throttle, would come back down quickly. Clutch never cut out though.
What is the best way to know if it is overfilled, or what to look for next? I am about ready to completely drain, replace that orfice, pump,then refill, but really do not want to do this if not necessary.
DesertStorm
06-10-2008, 09:46 PM
Well now see, that is what I did. I drained the A/C down to where the clutch would cut in and out rapidly. Then I hooked up my can of R-134a and began filling. Low side was around 18 - 20psi. Filled till low side had a reading of around 32psi. I checked my temp in cab, in center vent, a/c on max, fan on high, it read 78F. Brought rpm's up to 1000 then 1500, no change in temp. It was about 94F outside, I was in the shade, about 90F. Low side dropped to about 28psi. So I started filling again, till gauge showed 32psi, temp dropped to 62F, brought rpm's up to 1500, temp went to 60F. When I went back out to the gauges and revved the engine (do not know what RPM) high side would keep increasing, and let off throttle, would come back down quickly. Clutch never cut out though.
What is the best way to know if it is overfilled, or what to look for next? I am about ready to completely drain, replace that orfice, pump,then refill, but really do not want to do this if not necessary.
Still sounds like you have non condensables in your system. ie air,moisture. Pull a 30 min vacuum on the system and check for leaks. make sure your gauge stays pegged at 30" of HG. If it holds your good. Then charge. If you start from square 1 usually all problems and mis diagnosis will be eliminated.
DesertStorm
06-10-2008, 09:52 PM
[QUOTE=Bob Ayers;155451]Be very careful liquid charging that you don't slug the compressor.[/QUOTE
You are correct. It has to be slowly metered in. Not full blast but, 134A is a blend. It HAS to be charged as a liquid or some of the refrigerants will seperate and not be fully mixed in the system. Can cause some strange behavior. Only azeotropic HFC/CFCs can be charged as a vapor. R22/R12/R502/R500 etc etc. Old refrigerants.
now to charge as a liquid is to hold can upside down and vice versa for vapor, correct? Because every so often I "shake" (twist, whichever way you want to look at it) back and forth from 12 o'clock to 6 o'clock. Instructions on the can says to do this.
I was also wondering if my evap was dirty with dust\dirt, or who knows, maybe even mud from the P.O., would that not cause these symptoms as well? If so, what is the easiest way to get to it?
AllanD
06-16-2008, 02:48 PM
I'll add that if your engine is overheating you likely have an issue with a coolant radiator that atleast partially plugged OR you have a lazy thermostat.
My AC is working perfectly and even standing still in 95degree ambient temps the engine temp guage approaches, but never actually gets to the halfway mark
Typically the label on a '94 Ranger/Explorer evaporator housing
specifies 1.5lbs of R-134a
that is EXACTLY two 12oz cans of referigerant.
The typical Ranger/Explorer system is specified for 1.75lbs of R12.
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I ask again, to liquid charge, is this to hold the can upside down? And to do this, the best method would be how? short bursts, semi short bursts (i.e. short burst=10-20 sec, stop for 10sec then repeat\ and semi burst=20-30sec stop for 10sec then repeat).
AllanD
06-19-2008, 08:30 PM
When I am starting with an evacuated system
I add a 12oz can by holding it upside down and letting it all go in one shot.
the second can tends to go a bit slower, but you can still feel the
can "go light" as the compressor stops cycling.
Why use small cans? because you know how much is in them, I never really trusted the load cell in the recycling machine.
and besides that machine won't give up the referigerant when the level drops below a certain point, so you'll tell it to charge 1.5lb and it'll stop at 1.1 at which point you'll need to GUESS how much of a 12oz can is 0.4lbs:)
the ranger system holds 24oz or R134a so when the second can is empty
you are done.
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