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Old 08-04-2005, 08:47 PM
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A/C on = Overheat?

Well, I finally got the a/c system in my 71 Riviera (455) to get cold, using Freeze 12.....

When I bought the car, the man said the previous owner had installed an electric fan that turns on by itself (and it does) whenever the a/c goes on. -- by the way the a/c must've been hard-wired because it doesn't cycle, it just stays on. The fan is about....ballpark figure 1 and a half feet by 1 and a half feet, and it's placed between the radiator and the condensor.

Anyway, I was enjoying my nice cold car today on the way to work and realized that the temperature guage was past 200... I drove a lil more and realized it was borderline on 220... Now, it didn't overheat, not that I can tell.. (no smoke, no water overflowing, no bubbling up) but I don't like running it hot like that, just.. can't be good.. not that close to an overheat.

I can't really ask the previous owner anything about it as he's now passed away, but.... I did find a water-flow restrictor in the console, but I dunno what he had planned to do with it. (u know, it looks like it goes by the thermostat and makes the hole where the water comes in the neck smaller, so it flows slower, thus reducing heat i guess?)

I was told by a co-worker (I work at Pep Boys) that it might be the clutch on the fan? I'm thinking possibly.. I mean.. stock the car should have never overheated when the A/C was on, and i shouldn't really need any electric fan set-up.. right? Or maybe I should just take the whole clutch fan idea away and put a high powered electric fan? but. ehh.. I hate relying on electric devices, to be honest.


So... here I am... -- suggestions, anyone? hello? pleaseeeee
and thx in advance

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Last edited by Fragzem; 08-04-2005 at 10:59 PM.
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Old 08-04-2005, 09:03 PM
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I believe your set up uses an expansion valve(TXV) to control evaportor temperatures/pressure. This actually restricts or allows refregigerant flow through the evap core. It has a bulb & capillary tube that are attatched to eitther the evaporator fins or the low side tube at the evaporator. It measures the amount of superheat in the refigerant (completeness of evaporation) and opens and closes as necessary to maintain the preset amount of superheat. Thus, the compressor will not cycle. One question, did you use guages when you recharged? An overcharge can cause overheating due to more load. If charge is correct, and the car still heats, it could be a lack of airflow or coolant flow causing your problem. Look to see if a whole whack of the fins on the rad and conndenser cores are flattened or plugged up with bugs, dirt, weeds, ect. Also, make sure that there isn't any crap stuck inbetween the rad and condenser. Poplar fuzz, fine grass and dead grasshoppers have been known to pile up in there. Keep us posted!
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Old 08-04-2005, 09:11 PM
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Originally Posted by sbchevfreak
I believe your set up uses an expansion valve(TXV) to control evaportor temperatures/pressure. This actually restricts or allows refregigerant flow through the evap core. It has a bulb & capillary tube that are attatched to eitther the evaporator fins or the low side tube at the evaporator. It measures the amount of superheat in the refigerant (completeness of evaporation) and opens and closes as necessary to maintain the preset amount of superheat. Thus, the compressor will not cycle. One question, did you use guages when you recharged? An overcharge can cause overheating due to more load. If charge is correct, and the car still heats, it could be a lack of airflow or coolant flow causing your problem. Look to see if a whole whack of the fins on the rad and conndenser cores are flattened or plugged up with bugs, dirt, weeds, ect. Also, make sure that there isn't any crap stuck inbetween the rad and condenser. Poplar fuzz, fine grass and dead grasshoppers have been known to pile up in there. Keep us posted!
1. Yeah I'm also guessing it shouldn't cycle.
2. My grandfather put the Freeze-12 in there, and I know for a fact he only watches the low-side guage.. never even hooks up the high side... I'll have to check the high-side pressure myself as someone else suggested also.. we only put 3 cans in there tho and the compressor says "Riviera/Skylark = 4.50 lbs"
3. I could swear there's nothing stuck in the condensor .. looked at that fan 3x coz it was.. bothering me.. lol, and i dont believe i saw any debris on the condens. or radi... but maybe if i find some grasshoppers in there I can cook them

I'm really thinking this thermal clutch on the 7 blade fan isnt working properly..
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Old 08-04-2005, 09:35 PM
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Yeah, I like to see pressures on both sides. Usually on an avereage day(75-80*F) I like to see about 150 psi on the high side, and around 33-34 psi on the low side. Much lower that that on the low side, and you'll freeze off. It's not uncommon on a hot day to see the high side go to 250 psi. I prefer to charge on a hot day, as you get a better read, and you know darn well that it will blow cold. Also, look to see if it seems to be dripping a lot off the low side hoses. This can indicate an undercharge. Toss a thermometer in the vents, and put 'er on full bore. I like to see vent temperatures around 40-45*F, this usually puts the evaporator just above 35*F. Did you evacuate the system? This can actually drop evaporator temperatures by nearly 10*F. Moisture in the system is a major hinderance to efficient operation.


Airflow is a major concern to A/C operation and engine cooling. If the fan clutch is FUBAR, then this condition could occur. If the cores are clean on the outside, also look for scale buildup in the rad, as this could restrict coolant flow in the rad.
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Old 08-04-2005, 10:58 PM
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Originally Posted by sbchevfreak
Yeah, I like to see pressures on both sides. Usually on an avereage day(75-80*F) I like to see about 150 psi on the high side, and around 33-34 psi on the low side. Much lower that that on the low side, and you'll freeze off. It's not uncommon on a hot day to see the high side go to 250 psi. I prefer to charge on a hot day, as you get a better read, and you know darn well that it will blow cold. Also, look to see if it seems to be dripping a lot off the low side hoses. This can indicate an undercharge. Toss a thermometer in the vents, and put 'er on full bore. I like to see vent temperatures around 40-45*F, this usually puts the evaporator just above 35*F. Did you evacuate the system? This can actually drop evaporator temperatures by nearly 10*F. Moisture in the system is a major hinderance to efficient operation.


Airflow is a major concern to A/C operation and engine cooling. If the fan clutch is FUBAR, then this condition could occur. If the cores are clean on the outside, also look for scale buildup in the rad, as this could restrict coolant flow in the rad.
I'm definatley going to check the pressures tomorrow... and I'll come back asap and let you know.. thx for the help........ and the radiator will definatley get checked out..

SOmeone suggested to me to clean it with Preston's cleaner (not flush) and put some new water and anti-freeze in there.. i was figuring as much as well, since I just bought the car on the 28th and only changed the oil so far... tranny fluid looks good tho.

it's supposed to be 95F tomorrow... so ill look for 200+psi?
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Old 08-05-2005, 01:26 PM
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Yeah, I'd say between 175 and 200 psi high side would be about right.
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Old 08-05-2005, 09:05 PM
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If it makes you feel any better, my '72 Nova ran around 230* with the A/C running, and the only problem I had was the usual belch-out after turning the engine off. I added an aftermarket recovery tank and had no more problems until the A/C itself bit the dust years later. It was also of the non-compressor-cycling design.
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Old 08-20-2005, 12:45 PM
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NEW FAN CLUTCH. make sure it has the thermostatic spring on the front of it. your blade should be ok. Unless your radiator is blitzed.

freeze 12 is a 134 blend. I don't care what they say, if you don't put in 134 oil you WILL frag the compressor. experience has 100% failure rate 6/6 after freeze 12, until i started installing 134 oil.

Duracool is much a better freon. duracool.com
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