AC causes car to over heat

bdemat

Member
Sep 22, 2018
20
1
13
Acworth ga
Hello, every one, have a 90 mustang GT. Car runs great accept when I run the AC. Going down the road the air gets cool but not cold. When I am at idle, it gets warm and the car starts to over heat. Soon as I go down the road it starts to cool down again, both the temp and the AC. New radiator, water pump, thermostat, fan and fan cluch. I realize it's a airflow problem but the car is almost stock, what's the cure. Also while not running the AC the temp is perfect even at idle.
Any advise would be appreciated.
 
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MustangIIMatt

I need something stupid to play with
Mod Dude
Mar 7, 2002
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Hello, every one, have a 90 mustang GT. Car runs great accept when I run the AC. Going down the road the air gets cool but not cold. When I am at idle, it gets warm and the car starts to over heat. Soon as I go down the road it starts to cool down again, both the temp and the AC. New radiator, water pump, thermostat, fan and fan cluch. I realize it's a airflow problem but the car is almost stock, what's the cure. Also while not running the AC the temp is perfect even at idle.
Any advise would be appreciated.
Check your fan clutch. Drive the car until it's up to operating temperature, shut the car off, pop the hood, and try to turn the fan. If it turns easily, you need a fan clutch. If it has only slight resistance, you need a fan clutch. If it won't turn or is stiff as hell, it's not the fan clutch, you'll need to look elsewhere in the cooling system.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Check the air damn under the radiator support, it a plastic piece that runs vertical below the radiator, also there are two pieces, one on each side of the radiator that close off the opening. I would also make sure the condenser in front of the radiator is clean or does not have a bunch of junk between it and the radiator.
What temperature is it getting up to?
Has the ac been worked on recently?
 
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bdemat

Member
Sep 22, 2018
20
1
13
Acworth ga
I had it recharged about two yrs ago. The air damns are all intact but I did notice that there is quite a bit of over spray paint on the bottom of the condenser. About two inch high. Think that might have an affect but it just started this week. It runs normally at the lower quarter mark with out the AC. With the AC it got iin between the half and the 3/4 mark before I turn it off . I took the engine idle up and the engine temp started back down.
 

mikestang63

SN Certified Technician
Aug 27, 2012
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In the garage
the AC turned on adds more heat into the engine. You say you have a new radiator, fan, fan clutch, etc...
can you feel the air sucking into the condensor good or is it weak... a clogged condensor will cause this.
you can also take a hose and spray out debris caught in the condensor
Make sure there isnt any trash between the condensor and the radiator
Is your AC system in good shape? no clogs and fully charged
stock radiator or aftermarket.. did you get all the air out of it
are you running an overflow and is it working properly
did you put a new radiator cap on it and test it- is it 16lb
You sure you put the belt on right- dont laugh if you have it on the wrong way it will spin the water pump clockwise. the smooth side of the belt goes against the water pump pulley
Check the fan clutch to make sure it is working properly
Is the shroud good- not cracked and up against the radator
are all the air dams in place
The stock clutch fan pulls over 3000 cfm and should be sufficient to keep your car cool
 

bdemat

Member
Sep 22, 2018
20
1
13
Acworth ga
the AC turned on adds more heat into the engine. You say you have a new radiator, fan, fan clutch, etc...
can you feel the air sucking into the condensor good or is it weak... a clogged condensor will cause this.
you can also take a hose and spray out debris caught in the condensor
Make sure there isnt any trash between the condensor and the radiator
Is your AC system in good shape? no clogs and fully charged
stock radiator or aftermarket.. did you get all the air out of it
are you running an overflow and is it working properly
did you put a new radiator cap on it and test it- is it 16lb
You sure you put the belt on right- dont laugh if you have it on the wrong way it will spin the water pump clockwise. the smooth side of the belt goes against the water pump pulley
Check the fan clutch to make sure it is working properly
Is the shroud good- not cracked and up against the radator
are all the air dams in place
The stock clutch fan pulls over 3000 cfm and should be sufficient to keep your car cool
[/QUOT the radiator is new stock from AZ. I will try washing out the condenser and have the AC system checked. Question, how far should the fan be away from the radiator? Mine is 2, 2 1/2 inches away.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
You didn't say if there is a shroud.
You need to get a mechanical gauge and install even if it is zip tied to the wiper arm. This way you can tell what your temps are actually reading.
 

bdemat

Member
Sep 22, 2018
20
1
13
Acworth ga
I do have the factory shroud, but they don't sit flush on the radiator. There's about a 1/4 inch gap on both sides all the way down. The fan is about 2 to 2 1/2 inches from the radiator, I am wondering if I should get it closer with a spacer. It's an all stock car I am assuming that it was manufactured that way.
 

bdemat

Member
Sep 22, 2018
20
1
13
Acworth ga
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HoboNC

New Member
Mar 7, 2020
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Sanford, NC
Engine hot at idle while watching the fan turn the engine off if the fan keeps spinning you have a bad fan clutch. I like to see them not turn more than a few turns when I turn the engine off...