A/C rapidly cycles - '05 Impreza

[Dave Botsch]

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!

 

[Henry Paul]

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.

 

[Dave Botsch]

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 saying at fan speed 1 the compressor is cyling more often when
the engine is running at higher rpms (as in the car is in motion), ie the
compressor is cyling on and off more often than every 5 seconds (like, say
on for a second, off for a second)? That doesn't sound good at all.

 

[Henry Paul]

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?

 

[Dave Botsch]

Yes. temp control is on max cool. When the A/C is cycled on, the air that
comes out is quite cool. So, no problems getting cool air out.

 

[I'm Right]

if its cool out and cold in, duh

 

[Rob Munach]

Yes. temp control is on max cool. When the A/C is cycled on, the air that
comes out is quite cool. So, no problems getting cool air out.

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.

 

[tcassette]

My 96 Outback A/C has always cycled frequently. The dealer told me it was
normal. It has always cooled fairly well, but in the last 2 years or so the
A/C clutch makes a loud clicking noise whenever it engages for about the
first 15 minutes of operation on a hot day.

 

[Henry Paul]

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.

 

[Dave B]

Took it to the dealer. Service folk said cycling that rapidly in the low
fan speed position is completely and totallly normal.

 

[Edward Hayes]

Me thinks you may find the system low on freon. Have that checked with a
gage set to check hi and lo side pressure. Eddie

 

[Felix]

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