AC query, regarding on off - Team-BHP

tsk1979 · 5th April 2006, 11:57

Most air conditioned units and refrigerators have this warning. Wait for 3 minutes before restarting after a switch off. Infact newer samsung ACs when switched on do not start the compressor for 3 minutes after starting. There are also stabilizers which switch on after a delay.
Now come to the car scene. you will find your AC switching off and on frequently due to automatic climate control thermostat etc., If such frequent compressor on and off can damage the home AC, cant it damage the car AC or shorten the life? Or are car AC compressors made differently so that this does not impact them so much?

revharder · 5th April 2006, 12:47

in cars if you are manually doing that ON-OFF to the compressor than you are surely damaging the unit.

the machine itself diagnoses when the pre-set temp has reached it will cut off the compressor and will restart it on its own sensing the increase in cabin temperature.

same goes for the home ACs etc.
as soon as the pre-set temp is reahced compressor get cut-off. and gets restarted when any increase in temperature is noticed.

and that 3 minutes delay-start is used to protect the compressor from the fluctuations in electricity. say if the electricity is continuously fluctuating then that 3 minute delay will give you enough time to switch your unit OFF.
moreover, say, if units gets started and just after it got started, electricity goes OFF or fluctuates highly, then the unit may get damaged.
so that 3 min delay is used as precautionary measure to let the electricity supply stabilize!

turbo_c · 8th April 2006, 01:10

I think it has something to do with the fact that your home AC's compressor runs on electricty while your car's AC compressor is driven by the engine.

Your home AC's compressor is basically a large motor. Motors draw huge amounts of current when they are starting (upto 10 times the running current). That's why you may notice that the bulbs in your house dim slightly for a fraction of a second when the compressor starts up. The 3 minutes waiting is probably to give the compressor's motor windings time to cool off, since it might get quite hot with that huge starting current.

In your car, the worst thing that the AC can do by switching on / off often is increase the wear on the belt & clutch mechanism of the compressor but even with this, the compressor in your car would probably outlive the car itself !

- T u r b o C -

manik058 · 15th April 2006, 23:29

though being a newbie here, what i have known is that a compressor does the same thing as its name suggests. it comresses the gas and throws it into condenser with a high pressure, when a compressor is switched off the chain of compression and gas circulation stops and the gas(pressurised) in the condensor or pipes starts moving backwards to normalise the pressure in the whole unit. If u start the compressor b4 it gets normalize then it is surely gonna put extra load on the unit.
i guess it explains the 3 minute delay.

5th April 2006, 11:57	#1 (permalink)
tsk1979 Team-BHP Support Join Date: Feb 2005 Location: Noida, New Delhi Posts: 8,793 View My Garage	AC query, regarding on off Most air conditioned units and refrigerators have this warning. Wait for 3 minutes before restarting after a switch off. Infact newer samsung ACs when switched on do not start the compressor for 3 minutes after starting. There are also stabilizers which switch on after a delay. Now come to the car scene. you will find your AC switching off and on frequently due to automatic climate control thermostat etc., If such frequent compressor on and off can damage the home AC, cant it damage the car AC or shorten the life? Or are car AC compressors made differently so that this does not impact them so much? __________________ Reclaiming.....!

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5th April 2006, 12:47	#2 (permalink)
revharder BHPian Join Date: Jan 2006 Location: New Delhi Posts: 406	in cars if you are manually doing that ON-OFF to the compressor than you are surely damaging the unit. the machine itself diagnoses when the pre-set temp has reached it will cut off the compressor and will restart it on its own sensing the increase in cabin temperature. same goes for the home ACs etc. as soon as the pre-set temp is reahced compressor get cut-off. and gets restarted when any increase in temperature is noticed. and that 3 minutes delay-start is used to protect the compressor from the fluctuations in electricity. say if the electricity is continuously fluctuating then that 3 minute delay will give you enough time to switch your unit OFF. moreover, say, if units gets started and just after it got started, electricity goes OFF or fluctuates highly, then the unit may get damaged. so that 3 min delay is used as precautionary measure to let the electricity supply stabilize!

8th April 2006, 01:10	#3 (permalink)
turbo_c BHPian Join Date: Jul 2005 Location: Pune / Mumbai Posts: 130 View My Garage	I think it has something to do with the fact that your home AC's compressor runs on electricty while your car's AC compressor is driven by the engine. Your home AC's compressor is basically a large motor. Motors draw huge amounts of current when they are starting (upto 10 times the running current). That's why you may notice that the bulbs in your house dim slightly for a fraction of a second when the compressor starts up. The 3 minutes waiting is probably to give the compressor's motor windings time to cool off, since it might get quite hot with that huge starting current. In your car, the worst thing that the AC can do by switching on / off often is increase the wear on the belt & clutch mechanism of the compressor but even with this, the compressor in your car would probably outlive the car itself ! - T u r b o C -

15th April 2006, 23:29	#4 (permalink)
manik058 Newbie Join Date: Apr 2006 Location: ghaziabad Posts: 1	though being a newbie here, what i have known is that a compressor does the same thing as its name suggests. it comresses the gas and throws it into condenser with a high pressure, when a compressor is switched off the chain of compression and gas circulation stops and the gas(pressurised) in the condensor or pipes starts moving backwards to normalise the pressure in the whole unit. If u start the compressor b4 it gets normalize then it is surely gonna put extra load on the unit. i guess it explains the 3 minute delay.