Overheating with A/C on

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  #1  
Old 07-02-07, 09:55 PM
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Overheating with A/C on

Hello all,

Just wondering if any of you have any ideas as to why my '99 Dodge Neon overheats ONLY when the air conditioning is on (by overheat I mean a sudden and substantial rise of the temp gauge, usually sits around halfway up to the H, but when it overheats it quickly rises to about 3/4 way up... haven't seen it go all the way up yet). And doesn't even do it all the time, only some of the time, like usually only after it has been running for several minutes, and sometimes even while on the freeway with lots of air blowing through the radiator. However, it NEVER overheats without the A/C running. And once it does overheat, I turn off the A/C and the temp drops back down almost immediately.

I have tried:
1) Checking the coolant level - it never changes, topped off, so I'm not losing fluid
2) Changing the thermostat
3) Changing the radiator cap
4) Changing out the coolant, refilled with 50/50 mixture of antifreeze

None of that has worked, it still overheats. I have noticed that the power drop when I turn on the compressor is slightly more than it used to be. The air from the vents is just as cold as ever, so it still seems to accomplish it's intended function.

The temperature here is getting into the triple digits, so if anybody has any ideas as to why it is doing this, I would appreciate it. Thanks!
 
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Old 07-03-07, 05:08 AM
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Is the coolant flowing through the radiator, with the cap off you should be able to see the coolant moving through the radiator? Are the electric fans kicking in? Make sure the front of the condensor and the radiator are free of dirt, debris and bugs!
 
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Old 07-03-07, 06:52 AM
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8 year old car? Is the interior of the cooling system clean? Any buildup on the interior radiator and/or engine surfaces can alter heat transfer dramatically. When you turn on the A/C, your A/C condenser is heating the outside air that then passes through the engine radiator, essentially making it have to work harder, which it isn't doing well at. You might try a good cooling system cleaner. Also make sure any air dams, spoliers, and metal shrouds (underneath the car?) are in place, these are there to control outside air flow and direct the proper amount of air through the radiator.
 
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Old 07-03-07, 04:23 PM
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Thanks guys.

Yes the fan activates, both to keep the engine at operating temperature and activates when the A/C kicks in, and the radiator is free of debris.

Formula1, thanks for the explanation, it makes a lot of sense. I will clean out the system straight away. Although I do have another question in this case... do I absolutely HAVE to take it in to a shop to clean it out or is that something I can do myself with a garden hose and some special cleaner? Because I would prefer that method a lot more as I just moved and money is a little tight. Thanks!
 
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Old 07-03-07, 04:26 PM
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Yes you can do this yourself. They sell radiator flush kits at autostores. They are not expensive. You basically attach your garden hose to it. When you are done, you just want to run a gallon of distilled water through the system.
 
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Old 07-03-07, 04:35 PM
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Thanks! I shall give this a try!
 
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Old 07-21-07, 06:48 PM
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Ok I'm back... took so long because work sent me out of town for a couple weeks. Anyway, I've tried backflushing the radiator twice and using the radiator cleaner stuff... it still overheats with the A/C, although seems to take a little longer to do it. I have noticed one thing though, it only seems to do it when the temp is in the triple digits, it doesn't do it at night when it's like 80 degrees out side. I don't know if it is just too hot to run the AC or if it's a problem with the cooling system. I know the fan and everything works and comes on when it is supposed to. I would like to be able to fix it because when the temp is 100+ degrees is when I need the AC the most as it is a black car and gets really hot inside. Anybody have any other ideas?
 
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Old 07-22-07, 05:43 AM
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The fans are working, and you've done just about everything you could do on the basic side..........I'm sure coolant flows through the radiator.......The question is how much. As cheap as radiators have become in recent years I wouldn't even consider putting money into and old unit taking it to a radiator shop to see how many gallons per minute it's flowing........I'd simply replace it
My 71 Barracuda used to do the same thing when the radiator got to be about 6 yrs old
 
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