A/C compressor load is dependant on ambient temperature, interior temperature (if using recirculate) and blower motor speed. As more heat passes over the evaporater the refrigerant boils faster and returned to the compressor and more “pumping” is requiered.
On a mild day (75 degrees) high side pressure may be 150 PSI. On a hot day (110 degrees) discharge pressure can exceed 300 PSI and if you have a four cylinder engine you can feel the difference in load.
Whether or not there is more of a load on the A/C system with the windows or sunroof open would depend on how it is used. With the blower motor set on a selected setting and the cabin air set on fresh air the load would be the same. For example the blower set on the lowest speed, windows up or down, no difference.
If the windows are closed it is likely a comfort level would be reached and the fan speed reduced, reducing the load on the A/C system. If using automatic temperature control and the windows are open the fan may always run at full speed.
Most cars cycle the clutch to control A/C pressure. A couple exceptions are; 1989-1990 Chrysler C-bodies (variable displacement compressors), Dodge Caliber (clutchless variable displacement compressors). I’m sure there must be other late model vehicles that don’t cycle the clutch but over all it is of the minority.
For example this is from the 2009 Dodge Caravan service manual discribing the evaporater temperature sensor;
The A/C-heater control uses the monitored voltage reading as an indication of evaporator temperature. The A/C-heater control is programmed to respond to this input by requesting the Powertrain Control Module (PCM) or the Engine Control Module (ECM) (depending on engine application) to cycle the A/C compressor as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing.
The basic principle of refrigeration is that while we
So, you resurrected a 5 year old thread in order to post an incomplete sentence that tells us nothing?
When can we expect the next installment of your thoughts?
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I enjoyed this thread even if it was ancient. I missed it the first time.
My view is different as is often the case. With all the problems of the world, hunger; wars; rumors of wars; political hatred; people abusing or killing their own family members, there is not a Rolodex big enough for me to bother to list some guy who chooses for whatever reason he has to run his a/c with his windows down. I guess I envy those whose lives are so tranquil and un-busy they have time to worry about such things.
My best friend from the USA has lung problems, and at night even when it goes down to -20 degrees, he sleeps with an open window in his bedroom.
I used to work with a guy who drove his Rambler with the windows down while running the A/C. He claimed that it was because he liked fresh air, when–in reality–his A/C was so weak that he and his passengers would have suffered heat prostration if he didn’t keep the windows down.
I stumbled onto this forum in the hopes of finding out if opening my sunroof to get some sun on long work trips w the AC on contributed to the breakdown of my AC clutch.
In red is where the heat eventually broke the electrical connection causing it to stop engaging.
Nope. The A/C clutch doesn’t know or care if the sunroof is open.
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No dispute the A/C clutch has no knowledge of sunroof configuration, but if the sunroof allowed the interior to get hotter, that might conceivably cause the A/C clutch to activate more frequently. A relationship of sunroof and A/C clutch failure seems improbable though.
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