Author Topic: a/c compressor cycle times  (Read 177 times)

monkeydave

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a/c compressor cycle times
« on: September 20, 2020, 01:42:35 AM »
my a/c comes on for 5 to 6 seconds and then of for 9 to 10 seconds

this seems very short time, the a/c works perfectly cold

maybe it stays on longer the hotter the weather is, not sure


anyone else have this 5 to 6 seconds on and 9 to 10 seconds off cycle


i did hear that fast cycling is a sign of low refrigerant, the car is 2 years old with just over 10k miles   

jazzaro

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Re: a/c compressor cycle times
« Reply #1 on: September 20, 2020, 09:07:06 AM »
The amount of ON time depends by the amount of heat to be removed from the cabin.

ColinB

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Re: a/c compressor cycle times
« Reply #2 on: September 20, 2020, 09:27:40 AM »
my a/c comes on for 5 to 6 seconds and then of for 9 to 10 seconds

this seems very short time, the a/c works perfectly cold

maybe it stays on longer the hotter the weather is, not sure


anyone else have this 5 to 6 seconds on and 9 to 10 seconds off cycle


i did hear that fast cycling is a sign of low refrigerant, the car is 2 years old with just over 10k miles

I'm probably being dim here, but I don't quite understand.

On my car (which has manual control of the A/C, not climate control) I push the button, the green light comes on and stays on, and cold air comes out of the vents. Do you mean that on your car the green light comes on and off every few seconds (which doesn't sound right)? Or is there some other way of detecting that A/C is switching on and off?

If your car has climate control I would expect the A/C to function according to whatever inputs that system uses to control the interior environment (temperature, humidity, etc), and it may well switch on/off at fairly short intervals. I don't have that, so don't know how you detect if it's running or not.

culzean

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Re: a/c compressor cycle times
« Reply #3 on: September 20, 2020, 10:32:23 AM »
my a/c comes on for 5 to 6 seconds and then of for 9 to 10 seconds

this seems very short time, the a/c works perfectly cold

maybe it stays on longer the hotter the weather is, not sure


anyone else have this 5 to 6 seconds on and 9 to 10 seconds off cycle


i did hear that fast cycling is a sign of low refrigerant, the car is 2 years old with just over 10k miles

I'm probably being dim here, but I don't quite understand.

On my car (which has manual control of the A/C, not climate control) I push the button, the green light comes on and stays on, and cold air comes out of the vents. Do you mean that on your car the green light comes on and off every few seconds (which doesn't sound right)? Or is there some other way of detecting that A/C is switching on and off?

If your car has climate control I would expect the A/C to function according to whatever inputs that system uses to control the interior environment (temperature, humidity, etc), and it may well switch on/off at fairly short intervals. I don't have that, so don't know how you detect if it's running or not.

Well on aircon the input from the condenser sensor ( cold part ) sets the on - off times,  if the condenser is getting too cold and liable to freeze up it cuts out the signal to the clutch solenoid and disconnects drive to compressor ( the scroll type honda compressor is simpler and more robust than the piston ones with variable stroke,  but honda one has a fixed output volume depending on speed it is rotating so if system getting too cold the drive has to be disconnected - the piston type variable stroke ones can just alter the stroke to reduce output and the drive stays connected to compressor all the time ).   The noise of the fans is a good indication as the fans under the bonnet go on and off with the compressor clutch... I assume MK3 aircon same as MK2.  I have done tests with a temperature probe down the air  vent and different circulating fan speeds,  the higer the fan speed the less cold the air coming out of vents is - especially when outside temp over 25degC,  at about 27deg ambient with the fan running slow the vent air can get down to about 5deg, medium speed  about 7 to 8deg and at high speed 9 to 10 degC, and the compressor runs longer in hot weather,  with less off time.

If it is very hot I notice the clutch does not cut in and out at same frequency ( it stays on much longer ) as when weather is cooler, this is because the hot air passing over condenser does not cool it down anywhere near freezing point.  At temperature below 4 or 5 degC the aircon should not run at all as that is the danger zone for freezing.

The amount of ON time depends by the amount of heat to be removed from the cabin.

Exactly....
« Last Edit: September 20, 2020, 10:58:38 AM by culzean »
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monkeydave

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Re: a/c compressor cycle times
« Reply #4 on: September 20, 2020, 10:47:49 AM »
thanks guys

jazzaro

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Re: a/c compressor cycle times
« Reply #5 on: Today at 01:34:13 PM »
Well on aircon the input from the condenser sensor ( cold part ) sets the on - off times,  if the condenser is getting too cold and liable to freeze up it cuts out the signal to the clutch solenoid and disconnects drive to compressor ( the scroll type honda compressor is simpler and more robust than the piston ones with variable stroke,  but honda one has a fixed output volume depending on speed it is rotating so if system getting too cold the drive has to be disconnected - the piston type variable stroke ones can just alter the stroke to reduce output and the drive stays connected to compressor all the time ).   The noise of the fans is a good indication as the fans under the bonnet go on and off with the compressor clutch... I assume MK3 aircon same as MK2.
Many japanese cars use scroll type compressors, more reliable, quieter and efficient compared with piston compressors. Also small cars as Fiat 500, Panda and Citroen C1 use scroll type compressor, since they are cheaper.
Medium size eurpoean cars instead use variable stroke piston compressors, since they are more confortable: ok, they are a little bit noisier, but the power drag is constant so in low gears the car won't modify the gas response. Yes, you feel the difference between aircon ON or OFF, but in ON the gas response is moreorless always the same. My Jazz in 1-2-3 gear is instead much more slower at low revs with the compressor in ON, and I clearly feel when the clutch engages and disengages, especially in up and downhill; this is a little annoying, because in some seconds you have full torque avaiable, in some other seconds you have some torque less because the compressor has been engaged.
This effect is emphasized in small engines and manual gearbox (i.e the 1.3 6m Jazz), while CVT gearbox the effect is much filtered. Since japanese cars are very often sold with CVT in their major markets, we can understand why they use a scroll compressor, and why Renault and VW use variable stroke compressors in their Clio and Polos.
« Last Edit: Today at 02:25:54 PM by jazzaro »

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