does a/c make car run MUCH hotter?

[paulc]

my compressor needs to be replaced and i am curious as to whether or not the engine will run a lot hotter when using a/c or not. any input?

[924Sman]

Paul...With the AC on the coolant fans will run continueously which keeps the engine cooler. So in my experience in actually runs cooler when the AC is on. Doesn't mean the engine is less taxed running it but it is designed that way. Same with over heating, turn on the heater and the car drops in temp. Take notice of the temp gauge when you kick the AC on and you may see the temp drop. Sman

[carsontc]

my temp gauge does not change at all when AC is on

2nd radiator fan kicks in as soon as the AC switch is turned on

[Porsche944]

How much "hotter" the engine runs with the A/C on is a function of the outside (ambient) air temperature, air flow through the condensor, heat load from the passenger compartment, and the efficiency of the engine's cooling system.

It is not uncommon for the temp gage to climb when you are stuck in traffic, particularly on hot humid days.

However, as long as the engine's cooling system is functioning properly you should not have any problems.

[TSNAPCRACKLEPOP]

if it was a problem, porsche wound have designed an extra engine a/c unit, with the compressor integrated into the water pump.

[pearldrum]

my car gets hotter with the A/C on. One of my fans doesn't work though...

[speedy007]

why mention humid days as worse?
for this application the air molecules actually have more cooling effect, they have more moisture in each and because of this, their able to absorb more heat as they pass thru the heat exchanger. i believe you can verify this on your psychometric chart.
altho it may "seem" warmer because of the humidity.

[TCMdocs944]

Do a search of posts for "fan switches, thermoswitches, cooling problems" etc. There are a few great post that should fix the problem.

I think this is a great place to start on improving engine function/performance.

(hints)
get both fans working
change thermofan switch to a lower temp
change thermostat to lower temp if your brave
bleed, burp or whatever the system
if this fails to get both fans working ....
relays(do search)

This stuff is not $ intensive and fairly easy stuff. Just takes a little time and about a six pack.

[AaronM]

Originally posted by speedy007
why mention humid days as worse?
for this application the air molecules actually have more cooling effect, they have more moisture in each and because of this, their able to absorb more heat as they pass thru the heat exchanger. i believe you can verify this on your psychometric chart.
altho it may "seem" warmer because of the humidity.

Humid days are worse because the A/C dehumidifys air as well as cooling it. The more humid the air, the harder the A/C has to work.

Aaron

[speedy007]

not really,
the a/c is only a on and off function, using pressure regulators it runs aprox the pressure all the time, you will notice a difference in the air temp on the a/c discharge because of ambient conditions, but whats happening is the moister air needs more of the refrigerating effect to cool down.
my 88 944 has a stock 2 speed radiator fan switch in it so that when the motor gets to a certain temp the fans come on high speed. working most of the time on low speed. i know this because ive rewired it to come on only high speed, i felt the stock settings werent working well with the lt1 installation.
maybe i didnt read the first post well enough, the motor will run hotter with the a/c on but with the a/c off and same fan speed, mph and ambient temp the motor will run cooler on a more humid day than a drier one.
i believe.

[AaronM]

Originally posted by speedy007
not really,
the a/c is only a on and off function, using pressure regulators it runs aprox the pressure all the time, you will notice a difference in the air temp on the a/c discharge because of ambient conditions, but whats happening is the moister air needs more of the refrigerating effect to cool down.

If the more humid air needs more refridgeration effect for a given vent temperature, then that would cause a person to turn the A/C up higher, wouldn't it? It doesn't matter to me, since I almost always have the A/C on full-blast anyway, but I would imagine that most people don't run the A/C on MAX all the time.

And yes, the engine will build heat faster with the A/C running. As for it getting physically hotter, that should not happen. The thermostat will still open and close at the same temperatures so the operating temperature range should not change. However, the car will build heat faster since the condensor is immediately in front of the radiator and that means the air hitting the radiator will be hotter than usual.

Aaron

[speedy007]

the only action that happens is the a/c clutch is energized. either on or off. the temp is regulated by mixing different temp airs, either by electroniclly operating mixing dampers and/or controling the vacuum signal to the various parts such as the heater hot water valve. thats why/how the pressure regulating valves keep the system operating at aprox the same press/temp even thou the rpm is litterally going nuts up and down, normal driving.
max cold is usually 100% return air, or close to it. fresh ouside air is going to be warmer than the return air and is usually for the normal setting.
i believe.
and to turn up the control for more cooling is the wrong term, you can turn up the fan speed, but to get colder air, slow the air down and youll get more heat transfer than with faster moving air, it just doesnt feel as good as when the fan is blowing hard in your face. ever heard the secretary say to turn down the a/c because its too cold, shouldnt it be "turn off that friggin a/c and turn up the heat!"?
and when you adjust the temp in a 944 your trying to get the inside temp of the car, (the hole on your dash which sucks in the cabin air across a thermister on the floorboard by way of a small fan down there.) to match where your setting the dash knob, degrees. and this would be done thru the manner discribbed.
i believe.

[AaronM]

Originally posted by speedy007
the only action that happens is the a/c clutch is energized. either on or off. the temp is regulated by mixing different temp airs, either by electroniclly operating mixing dampers and/or controling the vacuum signal to the various parts such as the heater hot water valve. thats why/how the pressure regulating valves keep the system operating at aprox the same press/temp even thou the rpm is litterally going nuts up and down, normal driving.
max cold is usually 100% return air, or close to it. fresh ouside air is going to be warmer than the return air and is usually for the normal setting.
i believe.
and to turn up the control for more cooling is the wrong term, you can turn up the fan speed, but to get colder air, slow the air down and youll get more heat transfer than with faster moving air, it just doesnt feel as good as when the fan is blowing hard in your face. ever heard the secretary say to turn down the a/c because its too cold, shouldnt it be "turn off that friggin a/c and turn up the heat!"?
and when you adjust the temp in a 944 your trying to get the inside temp of the car, (the hole on your dash which sucks in the cabin air across a thermister on the floorboard by way of a small fan down there.) to match where your setting the dash knob, degrees. and this would be done thru the manner discribbed.
i believe.

Well, I wouldn't know. I've pretty much always got the A/C set to full cold and the fan on the highest setting.

Aaron

[speedy007]

me too

[Roadman_944]

My A/C compressor is disabled at present, but I turned it on one day on the way home from work in stop and go trafic just to see how much cooler it would run with both fans on. I was amased at how much it cooled. My guage went down to the first mark and stayed there. As soon as I turned it off it imediatly climed back to the second mark again. Normaly the cooling fan kicks on at just above the second mark and shuts off at the first mark. I live in Baton Rouge and it gets VERY hot here. I think it was 90*+ that day.

Any one have a usable A/C compressor for sale? I broke one of the mounting tabs off of mine. I managed to remount it to tighten the Alt. belt but I am afraid to use it. I have the wire disconected right now.

[UconnTim97]

my car runs hot in traffic, if I turn the AC on, it seems to cool the engine. But I am always nervous at how hot it gets. I think I have seen a few compressors for sale on ebay.

[AaronM]

Originally posted by UconnTim97
my car runs hot in traffic, if I turn the AC on, it seems to cool the engine. But I am always nervous at how hot it gets. I think I have seen a few compressors for sale on ebay.

Define "hot". From what I can tell, normal operation temperatures are between the top white mark and the bottom white mark. In town, the temp will usually climb up to or just past the rightmost white mark, at which point both fans will come on fully and the temperature will sink to the leftmost white mark at which point the fans will shut off and the temperature will begin to rise again. It took me a while to get used to, but it's normal. The radiator has poor airflow at low speeds, the car wants to be moving along at 40+ mph.

Aaron

[UconnTim97]

mine hangs in the far right in traffic, (yellow on my car) I still am not used to it.

[AaronM]

Originally posted by UconnTim97
mine hangs in the far right in traffic, (yellow on my car) I still am not used to it.

You might want to check on the radiator fans. Once the temp hits that rightmost mark the fans should both kick on at high speed (which is what having the A/C on forces). If the temp gets up there and doesn't come back down, then one of the fans might not be coming on. Just a thought.

Aaron

[UconnTim97]

The fans do turn on at the right most mark, but it doesn't seem to bring it down much. I tried it today without the AC on (90+ degrees out) and it never reached the right most mark. Maybe it is the AC that is causing it to run hot. I will check the fans out though. Thanx for the advice.