Sometimes it can get too cool in the car. I then dial back the temp a little. Does the compressor run just as much whether the temp is set to cold, midway or over to the red?
When you run your ac but set the temp at midway:
- Thread starter gypsyman
- Start date
my uninformed guess: with climate control with temp sensors, yes. on a regular hot cold slider no it just reheats the air more.
On a modern day car the A/C compressor only runs when the system determines that the cabin temperature is above the set temperature. Or if it is hot outside the compressor will run most of the time but on cooler days the compressor will cycle on and off more frequently.
Zenmervolt
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The compressor will cycle on and off based on A/C system pressures and engine load (the compressor will shut off on most modern cars if you floor the throttle, for example), not based upon temperature settings. You do not reduce compressor use by choosing a warmer setting if the A/C is still on. A warmer setting just changes the mixing proportions of air through the system via the blend doors. On most modern cars, if you set the system to "Defrost", it will automatically engage the A/C regardless of the master setting in order to dehumidify the air and more effectively defrost the windows. The "Max A/C" setting (typically only present on American cars, especially Fords) simply switches the airflow to recirculate, thus continuously cooling the same air from inside the cabin instead of drawing in hot air through the cooling system. This allows the cabin to cool down faster. It does not make the compressor run any additional amount.
ZV
ZV
ViviTheMage
Lifer
Somewhat on topic with AC in cars...but when I use my AC its all of the way to COLD, and the fans at 2 , out of 4 -- if its hot enough out.
when I get about .5 miles from home, or 1 miles I turn the AC off, and just let the fan go...I have thought it was better for the compressor for some reason. Rather then just letting it run until I park, and leave the AC on until I turn my car off.
when I get about .5 miles from home, or 1 miles I turn the AC off, and just let the fan go...I have thought it was better for the compressor for some reason. Rather then just letting it run until I park, and leave the AC on until I turn my car off.
Demon-Xanth
Lifer
- Feb 15, 2000
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Just as a side note, I tested it at the track, A/C on drops my 1/4 mile times by a quarter of a second.
Edit:
By drop, I mean I get 15.75 vs. 15.50
Zenmervolt
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Doesn't matter. The compressor has its own lubrication supply and doesn't gain anything from being given a cool-down prior prior to parking.
ZV
ViviTheMage
Lifer
Demon-Xanth
Lifer
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Zenmervolt
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Very, very indirect relationship and then only for systems that use an orifice tube instead of an expansion valve to control refrigerant expansion.
An A/C compressor will turn itself off when:
1) System pressure becomes too low.
2) System pressure becomes too high.
3) WOT is signaled from the throttle position sensor (most modern cars, but not all).
4) Evaporator becomes too cold and begins to ice up.
In systems that use a orifice tube, the flow of refrigerant is controlled by cycling the compressor since the orifice size is fixed. In systems with an expansion valve, flow is controlled via adjusting the expansion valve's orifice size.
Temperature setting really doesn't have an effect on how much the compressor runs since under normal conditions it is only turned off if the evaporator becomes too cold, which is independent of the temperature setting as the air is blended after it has gone through the evaporator and not before.
Fan speed, however, will have something of an affect on how much the compressor runs as higher fan speeds pass more air through the evaporator and help keep it from getting too cold. Lower fan speeds will result in the evaporator staying colder and the system will disengage the compressor more often to avoid having the evaporator ice up.
ZV
Jeff7181
Lifer
- Aug 21, 2002
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You're gonna make me dig out my MACS books, aren't you?
As far as I remember, Max AC runs the compressor continuously (or at full capacity if you have a variable displacement compressor)... barring the conditions you mentioned... WOT, damage to the system, overheated engine, iced evaporator, etc. Maybe that's changed in the past 7 or 8 years, but I kinda doubt it.
LTC8K6
Lifer
- Mar 10, 2004
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I'm sticking to my guns for now.
The compressor runs less if the temperature is set higher as far as I can tell. Both of my owner's manuals seem to indicate that higher temp settings are more economical and that Max or Recirc are the most economical supposedly because the recirculated air means the compressor runs less.
That can only be if the cycle time of the compressor is linked to the temp you set, I think.
I have confirmed that Max does not run the compressor continuously in either of my cars.
The compressor runs less if the temperature is set higher as far as I can tell. Both of my owner's manuals seem to indicate that higher temp settings are more economical and that Max or Recirc are the most economical supposedly because the recirculated air means the compressor runs less.
That can only be if the cycle time of the compressor is linked to the temp you set, I think.
I have confirmed that Max does not run the compressor continuously in either of my cars.
Jeff7181
Lifer
- Aug 21, 2002
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That's right... because it will run continuously until the evaporator starts to freeze over, you floor the accelerator, the engine is overheating or if there's some indication of a problem somewhere in the system. (not sure what kind of sensors they have now days) Your compressor cycles when set to Max AC because one of those conditions is being met.
funboy6942
Lifer
- Nov 13, 2001
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OK, MAX on cars all it does is closes the trap door from fresh air to recir the air in the car now, it really doesnt get colder because the compressor is working more, but because it is cooling already cooled off air, and not 100 degree outside air coming it, it is more efficient, and cools a hot car faster this way.
As for moving the slider for hot and cold. All you are doing is opening and closing yet the same trap door with a butterfly valve. It allows the hot air from outside to mix with the ac air. The more you move it to hot, the more it closes off the cold side and allows more hot air in. IT DOES NOT stop your ac compressor from working. The compressor has two modes for itself. ON and OFF, other then that it operates the same way for no matter really what you put the slider at. This is true for all the middle class cars out on the road with a slider to go from hot to cold which is activated by vacuum the engine produces. 50K cars and above may be different, I dont know, never worked on one as of yet with computer controlled temp stuff, but I would have to assume it works the same way opening and letting outside air in more, or less, depending on what the temp is set to.
Dont believe me, turn off your car and move the slider quickly for hot to cold and you will hear a door, or flap under the dash open and close. Start your car and move from floor-vents-dash, and you should hear a hissing noise and it uses a vacuum operated valve to go to the different spot on the cars dash.
When you have the ac going and turn it to max, the ac sounds louder, because usually the flap to recir the air is on the passengers side, near the heac/ac fan blower, which is why it sounds louder, and more like a real vacuum is being used in the car, but the whole time you going from norm to max, or hot to cold, have someone watch the compressor operation under the hood and see if the clutch ever disengages except for normal operation. it wont, because like I said the ccompressor has 2 modes, off, when the front part is not spinning, and op when you hear a click noise, rpms go down and back up, and the front part of the compressor clutches hook up and start to spin the compressor to make the compress gas to make cold happen.
Hope this helps, but in no way are you saving anything by making it 80 instead of 72 in your car other then making it uncomfortable for you because your thinking your saving gas when you are not.
OH on min settings, if you car has it, may be called BI-level, the compressor should be doing alot of turning on and off, as if the system is low on freon, other then that, its is still 2 modes, on and off, and the temp changes by opening a flap or falve under the hood to let more or less outside aitr into the car. Thats it.
As for moving the slider for hot and cold. All you are doing is opening and closing yet the same trap door with a butterfly valve. It allows the hot air from outside to mix with the ac air. The more you move it to hot, the more it closes off the cold side and allows more hot air in. IT DOES NOT stop your ac compressor from working. The compressor has two modes for itself. ON and OFF, other then that it operates the same way for no matter really what you put the slider at. This is true for all the middle class cars out on the road with a slider to go from hot to cold which is activated by vacuum the engine produces. 50K cars and above may be different, I dont know, never worked on one as of yet with computer controlled temp stuff, but I would have to assume it works the same way opening and letting outside air in more, or less, depending on what the temp is set to.
Dont believe me, turn off your car and move the slider quickly for hot to cold and you will hear a door, or flap under the dash open and close. Start your car and move from floor-vents-dash, and you should hear a hissing noise and it uses a vacuum operated valve to go to the different spot on the cars dash.
When you have the ac going and turn it to max, the ac sounds louder, because usually the flap to recir the air is on the passengers side, near the heac/ac fan blower, which is why it sounds louder, and more like a real vacuum is being used in the car, but the whole time you going from norm to max, or hot to cold, have someone watch the compressor operation under the hood and see if the clutch ever disengages except for normal operation. it wont, because like I said the ccompressor has 2 modes, off, when the front part is not spinning, and op when you hear a click noise, rpms go down and back up, and the front part of the compressor clutches hook up and start to spin the compressor to make the compress gas to make cold happen.
Hope this helps, but in no way are you saving anything by making it 80 instead of 72 in your car other then making it uncomfortable for you because your thinking your saving gas when you are not.
OH on min settings, if you car has it, may be called BI-level, the compressor should be doing alot of turning on and off, as if the system is low on freon, other then that, its is still 2 modes, on and off, and the temp changes by opening a flap or falve under the hood to let more or less outside aitr into the car. Thats it.
Zenmervolt
Elite member
- Oct 22, 2000
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Originally posted by: Jeff7181
You're gonna make me dig out my MACS books, aren't you?
As far as I remember, Max AC runs the compressor continuously (or at full capacity if you have a variable displacement compressor)... barring the conditions you mentioned... WOT, damage to the system, overheated engine, iced evaporator, etc. Maybe that's changed in the past 7 or 8 years, but I kinda doubt it.
I've been under the impression that the compressor always runs essentially continuously unless those conditions are met. The exception being that, in an orifice tube system the compressor has to cycle (or, in the case of a variable-displacement compressor, vary capacity) as that is the only way to regulate the refrigerant flow since the expansion orifice is of a fixed diameter as opposed to an expansion valve system that can regulate to some degree independently of the compressor's status.
I know for a fact on my older cars that the temp sliders only controlled the mixing flaps in the system and had no connection whatsoever to the electrical controls for the compressor. The only thing that the A/C system "knew" was that the A/C button on the dash was engaged or not, or whether one of the scenarios I mentioned in my other post was met (low/high pressure, icing, WOT).
ZV
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 11
- 81
Originally posted by: Zenmervolt
Originally posted by: Jeff7181
You're gonna make me dig out my MACS books, aren't you?
As far as I remember, Max AC runs the compressor continuously (or at full capacity if you have a variable displacement compressor)... barring the conditions you mentioned... WOT, damage to the system, overheated engine, iced evaporator, etc. Maybe that's changed in the past 7 or 8 years, but I kinda doubt it.
I've been under the impression that the compressor always runs essentially continuously unless those conditions are met. The exception being that, in an orifice tube system the compressor has to cycle (or, in the case of a variable-displacement compressor, vary capacity) as that is the only way to regulate the refrigerant flow since the expansion orifice is of a fixed diameter as opposed to an expansion valve system that can regulate to some degree independently of the compressor's status.
I know for a fact on my older cars that the temp sliders only controlled the mixing flaps in the system and had no connection whatsoever to the electrical controls for the compressor. The only thing that the A/C system "knew" was that the A/C button on the dash was engaged or not, or whether one of the scenarios I mentioned in my other post was met (low/high pressure, icing, WOT).
ZV
Right... that's what it does when Max AC is selected. When Max AC is not selected it will cycle the compressor more often as it doesn't need to run as often or as long to maintain the desired temperature (or temperature range depending on whether there's actually a temperature sensor) in the cabin.
On older cars yes (by older I mean 70's... I'm not sure how sophisticated they were in the 80's and 90's), they were either on or off and mixed warm/cool air to give you the temperature you wanted. But that's why newer cars are so much more efficient when running the AC compared to old cars... they don't run the compressor needlessly.
On a related note, my dad used to tell me it's not good to turn the A/C off immediately after turning it on. Is there any truth to that. Did it apply to olders systems and doesn't apply any more?
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