Car Overheats when running a/c

[catera00]

I've been searching the boards and Google for this and have seen some mention of it but no resolutions posted.

My car temp stays near the middle point on the gauge even in hot 100 degree weather. But as soon as I turn on the A/C and the A/C fan turns on, the temp goes right up to the red zone. This is true if I'm on the highway, in town traffic or parked in my garage (I tried killing myself to escape the problems this car has but it overheated and stalled out). Kidding of course =P

so the temp will go right up to the red zone within 20 seconds or less as soon as that A/C fan comes on. Then it goes right back to normal operating temp as soon as I turn off the A/C and the A/C fan shuts off.
The A/C fan is the key here. Nothing changes until it turns on.

The facts:

-I have what I believe to be an oil cooler/ heat exchanger coolant leak due to it leaking from the rear top of the motor. The bypass valve is new so it isnt leaking from there.

-I have to refill the coolant tank about once a month.

-I just replaced my alternator

-Radiator fins look strait.

-no garbage or leaves etc between the radiator and A/C radiator (condenser I think its called?)

-Cooling and A/C fans function and seem to be starting and stopping properly.

-I have pleanty of coolant in the tank. 50/50 pre mixed orange coolant.

-Have not had any A/C work done recently. (I read that an over or under charged that it will generate a ton of heat)
Had a new Compressor installed at the dealer 2 years ago.

-All hoses are good

-Replaced both Auxillary water pumps and heater bypass vales and had a coolant flush 1.5 years ago.

I'm in Arizona so I need to keep my A/C running at all times in the summer. So any help is very much appreciated.
Thanks.

[lakesidepark]

that is a very rapid rise in temp and drop in temp...are you sure that the engine is actually overheating? You covered the fan operation (full ON all three fans when AC is on). The aux water pump is not ON at this time but the heater aux pump should be ON.

I had noted with my car that the temperature in hot weather actually went down with the AC on!

Another note: the orange coolant (Dex-Cool) can form a gel-type of sludge if it is exposed to contaminants or air. however I might expect overheat problems regardless of AC setting if this was causing it. Still, good to address the leak.

i would at this point find a way to verify that what you are seeing on the gauge is actually what is happening with the temperature. May also need to check AC hi and low side pressures with a set of manifold gauges to verify the pressures are OK. I can only think (if the temp IS rising) that the AC compressor is either seizing, , has the wrong pressure (too high - if it was too low it wouldn't come on), or has too much oil that is backloading the compressor. Still, it would have to put on a lot of load to get the temp to rise soooo quick.

1) electronic problem causing temp sensor input error when AC is energized
2) AC compressor backloaded due to high pressure, clog, or seizing
3) Dex-cool sludge / gel clogging cooling system (but would expect symptoms regardless of AC setting)

[catera00]

Originally Posted by lakesidepark

that is a very rapid rise in temp and drop in temp...are you sure that the engine is actually overheating? You covered the fan operation (full ON all three fans when AC is on). The aux water pump is not ON at this time but the heater aux pump should be ON.

I had noted with my car that the temperature in hot weather actually went down with the AC on!

Another note: the orange coolant (Dex-Cool) can form a gel-type of sludge if it is exposed to contaminants or air. however I might expect overheat problems regardless of AC setting if this was causing it. Still, good to address the leak.

i would at this point find a way to verify that what you are seeing on the gauge is actually what is happening with the temperature. May also need to check AC hi and low side pressures with a set of manifold gauges to verify the pressures are OK. I can only think (if the temp IS rising) that the AC compressor is either seizing, , has the wrong pressure (too high - if it was too low it wouldn't come on), or has too much oil that is backloading the compressor. Still, it would have to put on a lot of load to get the temp to rise soooo quick.

1) electronic problem causing temp sensor input error when AC is energized
2) AC compressor backloaded due to high pressure, clog, or seizing
3) Dex-cool sludge / gel clogging cooling system (but would expect symptoms regardless of AC setting)

Yes, I see the gelled coolant on my engine block so maybe a flush for testing sake? But like you said, there is no cooling problems any other time so that most likely isnt a problem. I wont rule it out though

And that IS a ridiculously fast rise and fall of temperature. I dont see how an engine can come back down from overheat status with the red warning light on, to normal temp in like 3 seconds. I dont see how heat could dissipate that quickly sitting in my garage.
How can I test or verify that its actually getting that hot without blowing a head gasket? (And this question is for anyone that might know)
I am Being very cautious not to over heat it. I just had a new head gasket and head installed 2 years back and no longer have a warranty to pay for it.


Aux heater pump is flowing. Aux circulation pump comes on I believe when idling or when the heater is going.

What should the A/C readings be? I have a gauge I can slap on the high and low sides.

Thanks very much for your reply.

[catera00]

I looked at the bottle of coolant I used to fill up my tank a couple weeks ago and noticed I hadnt bought 50/50 mix. So I filled up the tank with 100% coolant. I wonder if that is having an effect on the temp? Still doesnt explain the rapid rise and fall but I figured I'd throw that out there.

[lakesidepark]

I do not know the 'spec' pressures. However on mine I am running at about 35psi low / 175psi high (80 degrees ambient temp at idle full ON 60 degree AC setting) with no problems.

I think you are right about the aux pump. It may also run when all fans are on HI. I'll look at my notes this weekend I made when i was investigating my overheat problems a couple of years ago.

I suggest try an experiment to see if it is actually AC load causing the rapid rise (it may work it may not). Try to locate the wire that plugs into the AC compressor clutch and disconnect; then test and engage AC. This will remove the compressor load but the fans should still come ON, if it was an engine load problem it should't show overheat; if it is an electrical problem it MAY show overheat (if it is an electrical load or short problem caused by the fan circuit it should show the same symptom). Also note the difference in your alternator load (voltage gauge on dash) and see if there is a drastic drop in voltage when fans kick in.

As far as measuring the actual engine coolant temp change when this happens to see if it is true? Not quite sure the best way to do that and see the response as fast as the gauge would see it. But I would think a thermometer on the stainless return tube passenger side would measure the heat rise quick enough to verify if the gauge is working right and you actually do have overheat before it is too late to shut down. Would try to use the most responsive temp probe or thermometer I could get - if the actual engine coolant temp is going to the red zone in 10 seconds you don't want to run too long past that.

[frank moran]

most all scan tools will read the temp as quicly as it rises. Try AZ, they may have a scan tool they could help you with. (A code reader wont do what you want).

[yermo13]

hello there!
well, very interesting i did what you suggest to unplug the wire that connect the AC compressor i let it ran and the temp. never rise like it was before but i really appreciate this suggestion and hopefully someone point us in the right direction to found out how to fix the electrical problem if it is a common problem..with instructions..
thanks you made my day...

for those that need to check this use your Car Jack to lift your car below your motor from the driver side you'll see the plug is easy to disconnet....

[catera00]

Originally Posted by yermo13

hello there!
well, very interesting i did what you suggest to unplug the wire that connect the AC compressor i let it ran and the temp. never rise like it was before but i really appreciate this suggestion and hopefully someone point us in the right direction to found out how to fix the electrical problem if it is a common problem..with instructions..
thanks you made my day...

for those that need to check this use your Car Jack to lift your car below your motor from the driver side you'll see the plug is easy to disconnet....

So youre saying it was the a\c load that was making your car overheat then and not the fans? that seems like a serious problem. I'm kinda thinkin my problem is related to another prob I am having with the battery not getting enough juice from the alternator. (I think its a bad battery cable). It seems like mine overheats when the battery is low. When the a/c fans kick in, the battery voltage drops down to the 1/4 mark on the gauge and I'm thinkin thats causing my cooling fan to not spin fast enough to cool the engine. When I hook up a battery charger and tun the ignition on I can hear the cooling fan speed up as soon as i turn on the charger. Just a theory at this point.

[frank moran]

Originally Posted by catera00

So youre saying it was the ac load that was making your car overheat then and not the fans? that seems like a serious problem. I'm kinda thinkin my problem is related to another prob I am having with the battery not getting enough juice from the alternator. (I think its a bad battery cable). It seems like mine overheats when the battery is low. When the a/c fans kick in, the battery voltage drops down to the 1/4 mark on the gauge and I'm thinkin thats causing my cooling fan to not spin fast enough to cool the engine. When I hook up a battery charger and tun the ignition on I can hear the cooling fan speed up as soon as i turn on the charger. Just a theory at this point.

you may have a bad pos bat cable, also check the condition of the alt wire that runs from the rear of the alt to the starter, this was a problem and a undersize wire at one point. The voltage drop when you put on the ac is not right. The best way to check the pos cable is to do a voltage drop on it, the cable may look good from the outside but they do build up corrosion under the insulation. This was a problem I had at one time with my 97. Also look the neg cable over .

[angelgalindez]

I bought a clean 97 Catera with only 39,000 miles about 5 weeks ago. The day I got it, it overheated on me (the a/c was on) and the radio went out whenever the car was on, but not when it was off... The dealer had the problem fixed for me, got it back to me the next day and said it was a wire to the radiator fan.

A few weeks go by and I take my car to the shop to get a few problems diagnosed (A/C, Temp controls, Cruise control). I was getting no cold air, and the air would flow only out of the front vents. It wouldn't switch between floor, windshield, and vents. Also the heat wouldn't come on...

The shop charges me for 4 hours labor and says the ac control head was unplugged. Refrigerant charge was low, and there was a leak at the compressor housing. He also said I should replace my alternator because the output was low @12.8 Volts and that the starter motor would not engage... He estimated me at $2,622.75.

I guess plugging in the "ac control head" was enough to get air flowing to the vents, floor, and windshield... and the heat works now too. I have ac for a little while since he recharged the system before finding a leak in the compressor housing.

I paid my $320 for 4 hours of labor and headed home to find a good deal on parts online and attempt the work myself since I just got a set of 97 Catera Shop Manuals. (this was yesterday 5/12/09)...

Today I get out to run some errands (I had the ac on) it was about 92 degrees today. After about 20 minutes of driving in about 92 degree heat my radio goes out and I hear a slight hiss coming from the fuse box area so I figure somehow I blew a fuse out of nowhere... Then I notice my temp gauge steady climbing so I headed home asap. I got home just as the temp light came on and it had just made it into the red zone. I park and noticed the orange anti-freeze pouring out the bottom. I couldn't get my hood open so I didn't see exactly where it was coming from but it was closer to the passenger side of the engine.

I finally get the hood open, the overflowing has stopped and I cant really tell where it game from... but while looking around I notice something unplugged. I get my shop manuals and find that its another water pump (electric) the one under the coolant tank. I didn't connect it back yet, engine too hot...

Now I'm starting to think that the dealer unplugged that ac control head and that water pump to prevent my car from overheating... Because before the mechanic plugged the ac control head back in I was driving around fine for about 4 weeks, no overheating, and radio was good.

Does anyone have any good advice on where I should start with this car? I really like the car and with only 39,000 miles I paid $5000. I thought I got a good deal. The car is really clean and drives great when not overheating... Sorry I made this so long. Any feedback is appreciated, thanks.

[angelgalindez]

I bought a 97 Catera with only 39,000 miles for 5k about 5 weeks ago. The day I got it, it was overheating and the radio went out (ac was on while this happened). I called the dealer and he had it fixed for me. He said the mechanic told him it was a wire to one of the engine fans. Once I got the car back I was doing some investigating around the engine and found that the heater water pump was unplugged. I plugged it in and it immediately came on and stayed on for awhile even while I had the car off. I then unplugged it until I did more research on it, I didn't want to drain the battery.

A few days after getting it back I noticed the ac was not getting cold and I could not get the air to circulate through the floor or windshield, it would only come through the front vents. Also the heat would not work either. I decided to buy a set of the dealership shop manuals on eBay for $60 to try and do some work myself. I figured I would have the shop diagnose this problem for me and then try to do the work.

The shop charged me $320 for 4 hours of work and said that the ac control head was unplugged, the refrigerant had to be charged and that my alternator was running low @ 12.8 Volts... Apparently plugging the ac control head in fixed my issue of not circulating the air to the appropriate vents (floor, windshield, vents) they all work now The shop also recharged the ac system but told me there was a leak at the compressor housing. So I'll have air temporarily until in all leaks out.

I took the car in on Saturday 5/9, I got it back yesterday 5/12. Today I took the car on a few errands and after about 20 minutes of driving the radio went out and I heard a sizzle coming from the fuse box. I figured I blew a fuse out of nowhere...odd. Then I notice the temp gauge start climbing (oh..no...) I headed back home asap. I pulled in just as the temp light came on. When I parked I saw orange coolant spilling out of the bottom. I couldn't get my hood open so I didn't see exactly where it was coming from but it was from the passenger side of the engine compartment. I believe it was from the coolant tank. I also checked the fuse box to find fuse 10 (CLAMP 15a) was fried. I replaced it, turned the ignition to ON and it instantly burned it up (dang). I must have a short somewhere...

After thinking about the issue for awhile I am thinking that the dealer took it to someone who just tried to bypass my real problem by unplugging some of my heating/cooling system (ac control head, heater water pump). I was driving the car and it was running great for 4 weeks, without ac... now that the ac control head was plugged back in though I get this overheating, radio out problem.

Does anyone have any idea of where I can start fixing this problem? Any feedback is appreciated, thanks

[R-Caddy]

May be Heater Valve. DO NOT let the engine overheat ! ! ! Or the heads will go! And yes, old wires can also be a problem, just like ones that some mechanics like to "splice"... Spend some time with split wire loom and electrical tape under the hood. You will find more that a couple inches of wiring that needs care and new covering.