Car AC Compressors: Speed Control & Temperature Regulation

[Charles123]

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

 

[Mech_Engineer]

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.

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.

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.

 

[Charles123]

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

 

[mindheavy]

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.

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.

 

[Charles123]

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

 

[mindheavy]

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.

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.

 

[Charles123]

"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...

 

[Charles123]

Example of speed variation (AC Inverter)
http://www.youtube.com/watch?v=gHHYnzgn-_M&feature=related