A/C rapidly cycles - '05 Impreza

When the A/C is on fan speed 1 and I am idling (can only actually tell when idling), the A/C cyles on for about 5 seconds then off for about 5 seconds repeatedly. Turning the fan speed up to 2 lessens the frequency of the cycles and so on for higher fan speeds.

While I believe A/C cyling is normal, is this frequency of cycling normal? If not, what could be causing the problem?

Thanks!

Reply to
Dave Botsch
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Think of it like the thermostat on your furnace. (if you have one of course) The furnace will cycle on and off according to your demand for heat. The duration of time the furnace is in operation depends upon the current temperature in the house and the temperature you set on the thermostat.

The car A/C works in a similar way. When you have the fan on low speed, you aren't putting as much demand on the system and it is able to satisfy the demand quicker. (that's where you get the cycling from) When the fan speed is higher, you are pulling more air across the evaporator warming it up faster and putting more demand on the compressor. This will make the compressor kick in and stay running longer.

At higher RPM the cycling will happen more often because the compressor is turning at a faster rate. Therefore, it is able to meet the demands faster. It works just like your refrigerator, except that the compressor in your fridge turns at a constant rate.

Reply to
Henry Paul

Right. However, it seems to me that cycling on and off every 5 seconds would place a lot of strain on the compressor and significantly shorten its life.

So, you're say> Think of it like the thermostat on your furnace. (if you have one of course)

Reply to
Dave Botsch

There might be a problem with the clutch itself or a sensor related to it. Do you have your temp control on max cold when you use your A/C? Also, do you notice a difference in the cycling rates when the temp inside the car is cold or hot?

Refrigerant is cool stuff. It boils at around -20F so if you keep it under pressure, it will stay liquid longer. The liquid passes into the evaporator with hot air blowing over it, this cools the air and boils the liquid. The gas runs through the compressor, which adds heat. It then runs through the condenser out in front of the radiator. There is condenses back to liquid and heads back to the evaporator.

This whole cycle takes a certain period of time. If the compressor runs too fast for too long, the liquid won't fully boil and it will make it back to the compressor. This is a very bad thing. That's why there is a clutch mechanism to cycle it on and off.

Do you have problems getting cold air from the A/C?

Reply to
Henry Paul

Reply to
Dave Botsch

if its cool out and cold in, duh

Reply to
I'm Right

Our 2001 Forester does that as well. I think it is a design flaw. It can't possibly be good for the compressor clutch and everything else. My

2004 Nissan might cycle every 60 sec under the same condtions.
Reply to
Rob Munach

Reply to
tcassette

You might have it checked out, but I wouldn't worry about it too much unless the system stops working. Mine cycles frequently as well, but mine works great as far as cooling. I have a '96 Impreza.

I had a Jeep Cherokee before. That engine would only see 2k rpm and above on the highway and the A/C in that rig worked the best around 2k so I had to run in a lower gear to keep the rpms high enough for the A/C to do me any good at all.

Reply to
Henry Paul

Reply to
Dave B

Reply to
Edward Hayes

Dave, I just picked up an '05 Impreza RS manual wagon last week and I have the same exact problem. I thought that it was about 10 seconds to recycling, but it defintely is a short cycle. Cud be 5 seconds. The system works fine and I have no other problems with the A/C.

--Felix

Reply to
Felix

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