Frequent A/C hiss above 2500 RPMS

[Thayer.Hirsh]

Hey all,
So, the dealership couldn't figure it out, other message boards
couldn't. Can you???

I have a 2007 2.5i Outback 5sp. Whenever I have the A/C on the
highway, every 10-30 seconds i get a hiss from the dash (what i
suspect is the expansion valve.) I can hear it over the radio and
get's quite irritating on long drives. Right after the hiss, i notice
that the A/C blows out much colder air. I hear nothing driving around
town and also notice that the cold air is more consistent, that is not
this cold air/ warm air cycle.

I did a little test in the parking lot and noticed that A/C will hiss
if i rev the car up to 3000rpms while in nuetral. Lower RPMs seem to
be fine for the A/C

Any ideas what could be wrong? Thanks for all of your help

 

[Porgy Tirebiter]

Hey all,
So, the dealership couldn't figure it out, other message boards
couldn't. Can you???

I have a 2007 2.5i Outback 5sp. Whenever I have the A/C on the
highway, every 10-30 seconds i get a hiss from the dash (what i
suspect is the expansion valve.) I can hear it over the radio and
get's quite irritating on long drives. Right after the hiss, i notice
that the A/C blows out much colder air. I hear nothing driving around
town and also notice that the cold air is more consistent, that is not
this cold air/ warm air cycle.

I did a little test in the parking lot and noticed that A/C will hiss
if i rev the car up to 3000rpms while in nuetral. Lower RPMs seem to
be fine for the A/C

Any ideas what could be wrong? Thanks for all of your help

What do the High Side/low side gauges say when you do this?

 

[AnneCULaw]

What do the High Side/low side gauges say when you do this?

Sorry, I'm not sure what the HIgh Side/low side gauges are. Is that
like the pressure before and after the expansion valve? Thanks for
the help!

 

[AS]

I have experienced the hiss you refer to due to:
- Low refrigerant charge, usually together with some gurgling.
- Defective expansion valves which sometimes get as bad as to squeal
when the compressor cuts in and out.

good luck!

 

[Thayer.Hirsh]

What do the High Side/low side gauges say when you do this?- Hide quoted text -

- Show quoted text -

Sorry, what are those gauges? Would you know anything about the
relation of RPM to the exapnsion valve?

 

[Thayer.Hirsh]

What do the High Side/low side gauges say when you do this?- Hide quoted text -

- Show quoted text -

Sorry, what are those gauges? Do you know if there is a relationship
between engine RPM's and the expansion valve use>?