Cycling Aircon

[leonb]

After not using my aircon for about 6 months (winter period), it did not want to work when using it for the first time. So I got it checked out by dealer. They said the compressor could not kick in because of low pressure, and refilled - apparently no leaks.

So it worked, but I could feel that it did not make as cold as when it worked previously.

I let the car idle, put the aircon on coldest setting. I then put my hand on the cold silver/metal part of the aircon pipe (the part that is not insulated in engin compartment), and listen to the the engin. Doing this, I could hear and feel that the compressor is working for about 1 min, then cuts out for about 30 sec, and then kicks in for about 1 min. This cycling continued.

Ambient temps is about 25 deg C. As I said, the air comming from vents is cold, but wen it get very hot (30+ deg C), I can feel the aircon struggling to make car cold fast. It used to be better.

Is this cycling normal? Somewhere I've read about the compressor tripping out of high pressure if the gas was loaded at a too high pressure. Is this a typical symptom?

Also, I read that with adding gas, oil needs to be added. What is this oil, and where is it normally added. What will happen if oil is not added during regas.

The car is a 99 C280.

Thanks

 

[jaymanek]

Normal... thats how the pressure is maintained in the system...

 

[Andy W]

The system has to be charged accurately by weight, if the system is overcharged the condenser back fills with liquid and leaves little room for the vapour to condense into a liquid thus increasing the discharge vapour presure which will cause cycling on the high presure safety switch. If your vehicle is fitted with a liquid sight glass (eye) on top of the receiver/drier check that is full while holding the revs of the car at about 2000 rpm, if it is bubbling then it is short, if it remains full it is charged, difficult to tell if overcharged. The two pipes that pass through the bulk head, a large pipoe and a small pipe, the large pipe should be cold and wet the small pipe should be warm, if the small pipe is very hot it will cycle on hp switch as either your condenser coil is blocked with dirt, the condenser fan is not running or it is a hot day and you need to be moving to allow air to be forced through the condenser. If the big pipe is cold and wet and the small pipe is cool then probably overcharged.

Dont overlook the obvious that the system is cycling correctly on temperature.

Hope it helps.

 

[Glenn Smith]

The only way to properly diagnose is to run with gauges fitted to the high and low side, one simple check is to check condensor is not blocked and that heater is not hot due to leaking valves.

 

[leonb]

Normal... thats how the pressure is maintained in the system...

I cant believe it is normal for a compressor (or any other machinery) to cycle on/off in 30 sec intervals.

I used to see condensed water dripping from underneeth the car when using the A/C. I dont see any water drops anymore. Could this indicate the problem?

 

[fnkhan68]

my w124 has f/f aircon and the compressor works intermittently, ive been told that the are supposed to work like that to maintain the pressure and temperature. i still get cold air regardless.

 

[Andy W]

I cant believe it is normal for a compressor (or any other machinery) to cycle on/off in 30 sec intervals.

If it cold inside the car it will cycle as there is what we call "no load" on the evaporator, if you warm the car interior up first then put it on cool the evap will be loaded and then run longer, if it is not blowing cold then you have problems with the system either gas charge or expansion device or blocked filter drier to name but a few.

 

[blassberg]

Cycling aircon? My bike doesn't have that option...