Car AC Compressors: Speed Control & Temperature Regulation

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Discussion Overview

The discussion revolves around the control mechanisms of car air conditioner compressors, particularly those driven by engine belts, and the differences between air conditioning systems and refrigerators. Participants explore how compressor speed is managed, temperature regulation methods, and the implications of refrigerant circulation.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that in belt-driven compressors, speed is not controlled; rather, the compressor operates through an on/off solenoid clutch based on system pressure.
  • Others argue that the compressor's operation is influenced by the engine's idle speed, which must be sufficient for proper compressor function.
  • There is a suggestion that temperature control is achieved through vent door adjustments in the passenger compartment, rather than through compressor operation.
  • Some participants question the role of refrigerant velocity in cooling efficiency, noting that adequate high-side pressure is necessary for cooling to occur.
  • A later reply mentions that electric air conditioners are becoming more common, especially in hybrid vehicles that can turn off the engine during stops.
  • Participants discuss the core differences between air conditioning systems and refrigerators, noting that different refrigerants are used due to varying operational requirements.

Areas of Agreement / Disagreement

Participants express differing views on the control of compressor speed and the role of refrigerant circulation in cooling efficiency. There is no consensus on the effects of refrigerant velocity on cooling rates, and the discussion remains unresolved regarding the specifics of temperature regulation methods.

Contextual Notes

Participants highlight that the discussion involves assumptions about system pressure and the operational characteristics of different air conditioning systems. The implications of refrigerant type and system design on performance are also noted but not fully explored.

Charles123
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How is the compressor speed controlled in a car air conditioner, in compressors driven by engine moved belts? Is temperature controlled just by on/of of the solenoid clutch?
Electric air conditioner (automotive), not driven by (directly) by engine, is widely used today?
Another question, not related to car systems. What are the core differences between ac and refrigerators? Is the refrigerant type the main issue?
Thank you
regards
 
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Charles123 said:
How is the compressor speed controlled in a car air conditioner, in compressors driven by engine moved belts? Is temperature controlled just by on/of of the solenoid clutch?

Yes, the compressor is switched on and off as needed by monitoring the system's high-side pressure.

Charles123 said:
Electric air conditioner (automotive), not driven by (directly) by engine, is widely used today?

There are some models out there that utilize them, mainly vehicles with engines that automatically turn off during stops such as hybrid vehicles.

Charles123 said:
Another question, not related to car systems. What are the core differences between ac and refrigerators? Is the refrigerant type the main issue?

Analytically they are basically the same. They use different working fluids due to different operating requirements.
 
Thank you for your answer.
So in belt driven compressors their speed is not controlled, there is just an on/off switching as needed, doesn’t matter the engine rpm? The temperature is just controlled by this plus the mixture of air that passes through the evaporator and air that does not?
Related to refrigeration systems, their core dimensioning factors would be what? Compressor speed? Pipes diameter? Plus as you mentioned the refrigerant type…
Regards
 
Charles123 said:
So in belt driven compressors their speed is not controlled, there is just an on/off switching as needed, doesn’t matter the engine rpm?

The minimum engine idle speed (RPM) is high enough to allow proper operation of the compressor. The 'click' you hear as a car is running with the A/C on is the compressor clutch engaging and disengaging to either build up pressure (the high side pressure Mech_Engineer spoke of) or stop building up pressure. Once this pressure reaches a low enough point, the compressor clutch is once again engaged.

Charles123 said:
The temperature is just controlled by this plus the mixture of air that passes through the evaporator and air that does not?

Temperature is controlled by moving vent doors inside the passenger compartment. Not the compressor.
 
Thank you for your answer.
"The minimum engine idle speed (RPM) is high enough to allow proper operation of the compressor. The 'click' you hear as a car is running with the A/C on is the compressor clutch engaging and disengaging to either build up pressure (the high side pressure Mech_Engineer spoke of) or stop building up pressure. Once this pressure reaches a low enough point, the compressor clutch is once again engaged."
But the compressor keeps running at all times?
“Temperature is controlled by moving vent doors inside the passenger compartment. Not the compressor.”
But the velocity of the refrigerant fluid circulation doesn’t affect the rate of cooling, like in other AC systems?
Regards
 
Charles123 said:
But the compressor keeps running at all times?
No. If the compressor clutch is not engaged, the compressor doesn't run. Only the pulley continues to be driven by the belt.
Charles123 said:
But the velocity of the refrigerant fluid circulation doesn’t affect the rate of cooling, like in other AC systems?
Regards
I'm not certain what effects the velocity of the refrigerant has on the rate of cooling. When there is an adequate amount of High Side pressure, cooling will take place. And once that pressure drops to a low enough amount, the compressor clutch is told to engage, and the compressor starts building High Side pressure again.
 
"No. If the compressor clutch is not engaged, the compressor doesn't run. Only the pulley continues to be driven by the belt."
Of course...

"I'm not certain what effects the velocity of the refrigerant has on the rate of cooling. When there is an adequate amount of High Side pressure, cooling will take place. And once that pressure drops to a low enough amount, the compressor clutch is told to engage, and the compressor starts building High Side pressure again."
If the refrigerant is not circulating there will be no cooling...
 

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