AC goes from frigid to cool to frigid...

[jws3]

"AC goes from frigid to cool to frigid..."

 

Sounds remarkably like my ex wife........

[havanahjoe]

The cause is the compressor. Subaru uses a fixed displacement cycling clutch compressor system where the a/c compressor runs for a few seconds to minutes, then shuts off, cycles back on.... ad nauseum. This is because as the compressor runs and the refrigerant temperature starts to drop, the a/c low side pressure also drops to the point where the compressor shuts off. This was not a problem in 1976 when most auto a/c systems held 3-4lbs of refrigerant, there was a large buffer of cold refrigerant and a huge evaporator coil to prevent temperature fluctuations. The average auto a/c system today holds 1lb of refrigerant or less. Most modern cars (and oddly enough 1989 - 1994ish Legacys) use a variable displacement compressor that adjusts the compressor displacement based on a/c load. A variable displacement compressor never shuts off during a/c operation as long as the refrigerant charge is correct, and therefore there are no temperature fluctuations.

 

I've considered retrofitting an early Legacy compressor and bracket, but it would require custom lines.

 

Thanks for the explanation. Do cars use less refrigerant now to be better with the environment? Or what's the reason for this?

 

It sounds logical to me that there is no easy way to fix this without doing major work to the AC system, otherwise Subaru would have done it from the factory or a simple aftermarket solution would exist.

[Yamarocket630]

Cars don't "use" refrigerant unless there is a leak.

 

Lower charge systems cost less to build, (smaller heat transfer coils, smaller compressors, less refrigerant, less lube oil) and smaller compressors have lower power requirements. Back in the olden days, A/C compressors sapped 20+ hp when in use. The scroll compressor on our 2005+ Legacy uses about 5-8hp.

 

The real reason Subaru is using a cycling clutch compressor is cost. The scroll compressor in particular is very cheap to build, as it only has 2 moving parts. Variable displacement compressors are much more complex and costly.

[tbssubaru]

fwiw my car is having this problem and the dealer is replacing the compressor and evaporator under the extended warranty

[havanahjoe]

fwiw my car is having this problem and the dealer is replacing the compressor and evaporator under the extended warranty

 

It didn't use to do it before? I've learned to live with mine. Luckily it doesn't get too hot around here, so it works well on the warmer days.

[tbssubaru]

i don't remember it happening last summer , we'll see if their repair resolves it

[tbssubaru]

got my car back yesterday , the dealer put in a new compressor and condensor which was covered by the extended warranty and the a/c works much better , i don't notice the cycling now