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Engine overheating when ac is on
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manedg
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Aug 12, 2012, 5:16 PM
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Engine overheating when ac is on
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Hi AC gurus. I got 95 mitsu montero sr with 185k miles. First mechanic replaced comrpressor with reman around 145k. Cold air did not last long, mechanic 2 replaced expansion valve and worked fine. After a few months. engine overheats when idling. Mechanic 3 replaced evaporator, expansion valve, and condenser, still overheats on idle. At idle. lowside is 35-40, high side -s 250. At 2500 rpm, lowside is 55, high side -s 350, temp is 60degrees. I noticed that compressor is always engaged on idle and 2500rpm. Replaced both compressor and ac fan relays, still compressor is always engaged. Engine does not overheat when ac is off in heavy traffic. Is reman compressor causing engine overheat? Thanks.
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Hammer Time
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Aug 12, 2012, 5:36 PM
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Re: Engine overheating when ac is on
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Sounds more like a fan clutch problem.
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manedg
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Aug 12, 2012, 6:52 PM
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Re: Engine overheating when ac is on
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I forgot to mention that the fan clutch was also replaced but it did not help. Yesterday, I had the radiator replaced as well. After everything was in place, I thought he got it working because I saw the compressor and fan turn on and off a couple of times, and then that was it, the compressor was engaged again all the time. During radiator replacement, he also tested the thermostat in boiling water, it does open at boiling temp. We don't know what to do next, and no, I have no intention of getting rid of this vehicle. Thanks.
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Hammer Time
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Aug 12, 2012, 6:57 PM
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Re: Engine overheating when ac is on
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You have to have some type of restriction to the air going through the radiator. The air conditioner cannot be the cause of the overheating. Something else is the root of that issue. The A/C just works it a little harder.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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manedg
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Aug 12, 2012, 7:29 PM
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Re: Engine overheating when ac is on
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I am actually thinking about that too. However, I am wondering though why the engine doesn't overheat in heavy traffic when ac is off.
One thing I notice though, is that the digital temp goes high on idle even when ac is off, but engine doesn't overheat. On this case, could it be that the the computer is sending signal to the compressor to work harder?
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Hammer Time
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Aug 12, 2012, 7:33 PM
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Re: Engine overheating when ac is on
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No, the compressor is either on or off. It labors the cooling system more so concentrate on that. Your A/C pressures also point to lack of air flow.
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manedg
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Aug 12, 2012, 7:40 PM
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Re: Engine overheating when ac is on
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At this point, can you give me any suggestions on what to do next? Thank you so much.
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Hammer Time
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Aug 13, 2012, 3:09 AM
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Re: Engine overheating when ac is on
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I've already told you. The area that would affect both the AC and engine temp would be air flow across the radiator and condenser.
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Tom Greenleaf
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Aug 13, 2012, 5:31 AM
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Re: Engine overheating when ac is on
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Lot's of stuff already on this and quite apparently is a "heat transfer" issue or lack of. Air flow as Hammer suggests would be highest on the list. New fan clutch could be junk out of box - got the T-shirt on those.
High side pressure is too high for me and points right to airflow issues as long as charge is known good. There's a 'maybe' clue in that this will run fine w/o A/C on which does add heat and load to engine but can handle that to a point so I wonder about general engine cooling ability with so many cooks in this kitchen already not finding exact problem yet just maybe cooling system for engine alone needs more checking.
Things like is water pump producing enough flow, hoses allowing enough flow. Air dams and shrouding all intact. Engine has some system to act as a by-pass such that water pump is continually pumping coolant around to maintain uniform engine temp. Can't know or spend a day figuring out each design for each model of everything ever made but could be a separate hose, use heater core or built into design of water pump on the engine most commonly.
A problem here would be rare but some elusive issues come from engine back heat as in it could be hot enough in the wrong places to defeat what should be adequate air flow. That would be rare as said but if this remains elusive with all other things ruled out I'd be chasing that as a cause,
T
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Hammer Time
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Aug 13, 2012, 5:47 AM
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Re: Engine overheating when ac is on
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Although a water pump with the fins rotted off could explain the overheating, I wouldn't expect it to effect the A/C pressures the way it is.
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Tom Greenleaf
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Aug 13, 2012, 6:19 AM
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Re: Engine overheating when ac is on
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Understood. Somehow, somewhere heat is not being exchanged at the places needed..............??
T
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manedg
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Aug 13, 2012, 7:05 AM
Post #12 of 17
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Re: Engine overheating when ac is on
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Thanks to both of you. Water pump(oem) was replaced at 145k which is 2 - 3 yrs. ago together with valve stem seals, timing belt, belt tensioner, etc.
I checked the pressure this morning(82F) whle the engine is cold and here are the readings...
at idle
low side - 35
high side - 180
at 2500rpm
low side - 30
high side - 180
AC temp inside the car was 58degrees F
I'll drop the vehicle this weekend to a reliable shop and have the engine temp checked. BTW, the fan clutch was aftermarket, I wonder if it needs an oem.
Is it normal for the compressor to be always engaged though? I am still thinking that the compressor is putting a lot of load to the engine at idle speed. The label under the hood says 27oz is required for R134a, I remember the last mechanic putting 24oz, I wonder if addign 3oz more would make the compressor on/off.
Again, thanks for the help.
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Hammer Time
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Aug 13, 2012, 7:25 AM
Post #13 of 17
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Re: Engine overheating when ac is on
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Stop assuming something is good just because it was previously replaced. That means nothing.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
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Aug 13, 2012, 7:43 AM
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Re: Engine overheating when ac is on
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Just notes:
Fan Clutches: Probably most OE are made to spec by an outside concern so I can't say every 'aftermarket' one is bad or even has the propensity to fail or not be up to par by that alone.
At a loss to describe exactly what you should expect by more that an experienced feel, sound of air flowing strong when it should. Some may not be thermostatic and just pull the same amount warmer or cooler - a waste if so. Fan blades with one that is pulling plenty of air thru is doing its clutch thing and firming up its grip meaning a high percent of pulley speed is also the fan speed and if so in that state that fan should stop turning quite quickly with engine shut off (by a helper) right in front of you. It wont coast much in that state if spun with a stick (keep hands out of fans please) as adequate proof that it is working.
Your pressures noted and temps: The thermodynamics is so pressure/temperature sensitive you need to know real temps at exactly the locations needed. Not a forecast but the real temps of air vehicle is dealing with and real output temps taken best at a center vent in cabin. The air temp in general inside a vehicle isn't the point yet.
In your test it seems engine was cool and no flow to radiator yet. Radiator is after the condenser and shouldn't be a huge factor and systems designed for that.
Right now your pressure look good but unsure of real temps noted. The 3 ounce undercharge known to that is probably a thought out decision by the tech charging it. I'll suggest to default to slightless less than slightly more when things demostrate a need to deviate from any known exact weight of charge. Real close is still critical.
Still thinking. This vehicle is not listed as one with common problems from new like you are experiencing that I could find,
T
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manedg
Novice
Aug 13, 2012, 10:09 AM
Post #16 of 17
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Re: Engine overheating when ac is on
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Ok folks, I think I am starting to see the light at the end of the tunnel. I did a little reasearch and the people at cartalk.com mentioned that If the coolant looks murky, it could be a sign of a blown head gasket.
Prior to having the radiator replaced over the weekend, I drained the radiator and indeed it was murky. This is actually the reason why I had the radiator replaced. Transmission oil runs through the bottom of the radiator and I thought the radiator is somewhat leaking oil and it is getting mixed with the coolant. No wonder the ac fan and compressor engaged/disengaged during the first few minutes after the radiator has been installed. I can bet with myself that if I drain the cooloant again, it will be murky.
I am bit surprised though that oil pressure reading looks nornal at idle and high engine rpms.
Thank you so much for all the info, I think I know what direction to take for now.
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Tom Greenleaf
Ultimate Carjunky
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Aug 13, 2012, 12:31 PM
Post #17 of 17
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Re: Engine overheating when ac is on
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I think we call all agree on one thing - no engine = no A/C so take care of engine, cooling system flushed with soaps or whatever it takes to be clean of oil. Bad enough to have oil in coolant and horrors if coolant gets in trans or yikes - both ways! Trans fluid or oil in coolant will be more than just murky it can get like shaving cream. The overheating then brings about the head gasket concerns so chase that to rule it in or out too.
First things first. Hope it cooperates and limited problems from the oil,
T
(This post was edited by Tom Greenleaf on Aug 13, 2012, 12:35 PM)
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