ac compressor cycling

[JungloSonic]

Very strange.. I checked a 2012 sonic Lt with 1.8L that a body shop was selling. The compressor on it was also cycling every few seconds as was the fan...very much like mine but Ozonetrooper, yours does not do that..so what gives..are older models designed to cycle rapidly? I will check other similar cars if I get a chance.

 

[ozonetrooper]

I am not saying the cycling may not be normal, I am saying, that in all of the years and things I have worked on, that is not how everything else has worked.

 

[JungloSonic]

Thanks for the clarification. You said that yours does not cycle like this. Did you check that or did you assume this based on experience and that your ac cools fine or did you look at the physical compressor? Mine works to cool the car but looking at the compressor, cycles frequently (maybe in hot weather it will stay on a bit longer?). My concern is that if the compressor cycles too frequently, the compressor clutch might quit sooner than later.

 

[ozonetrooper]

Let me clarify even more !

If the compressor is not running it is not making cold air and the air coming from the vents will be warmer than when the compressor is on.

It has just started to cool off here but we have just dropped down from triple digit weather. Even my white color does not keep the car from getting hot inside when not in use.

I ride with a vent blowing on me and I am sure I could tell if the compressor is cycling instead of constant running.

'sides, I have done alot under the hood, and know from watching the clutch on the compressor, it stays locked up when the a/c is on.

My fan does not run unless the a/c is on, and it does cycle off and on.

 

[JungloSonic]

so my a/c compressor used to turn on for longer. over time it has gone from 10 sec on time to now 4 sec on time..then off for about 12 sec then repeats. Is a small leak a likely cause or could it be a sensor (like pressure sensor). Does pressure sensor degrade gradually or is it usually binary (works or doesn't). I had replaced the high pressure line that has the pressure sensor attached. All were tightened to spec except the sensor which I estimated to around 8 ft/lbs..then the system was refilled. The low pressure when the car has been off for an hour or so is reading around 67-70 psi

 

[JungloSonic]

does anyone know the torque spec for ac pressure sensor?

 

[ozonetrooper]

I believe the pressure sensors either work or they don't.

There are a few things that can cause the compressor to short cycle.

Is your radiator fan running ?

In the off cycle the low side pressure is usually equal to the high side, with the low side gauge being against the stop/120+ psig.

 

[JungloSonic]

yes, the radiator fan runs (cycles). I don't think the low side gets to 120 psi but I need to get checked out.
I thought the sonic doesn't have a low pressure switch.. just high pressure switch (transducer) on the high pressure line by the compressor? Also I have noticed that as the weather is starting to warm up (17 degrees celcius) , the compressor cycles a bit longer on the "ON" position before cycling off.

 

[ozonetrooper]

I have read that the outdoor air temperature sensor has input to the compressor run time.

My OAT sensor does not show on my radio screen but my a/c does work as normal.

 

[JungloSonic]

Well then I will track the compressor "On" time as the temperature warms up further.

 

[bbsux]

OP make sure the radiator fan is running. My 2013 would cycle like that when the fan not was running (At idle AC would work fine when driving around cause the ac radiator got cooled by the air). Check the fuze in the box (with a multimeter cause those J type fuses can be hard to see sometimes) I replaced my fan before I figured out it was the fuse because it looked good

 

[JungloSonic]

When I have a/c on and recirc off, the compressor seems to be on for longer before cycling off especially on hot days. When on recirc, it cycles more frequently. When cabin fan is on on HIGH leads to longer compressor on cycle before cycling off. The radiator fan seems to cycle on/off and I think that is normal.