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Discussion Starter · #1 ·
Hello all, and thank you in advance!

A/C recently stopped working in my 2004 Subaru Outback Limited (CA-spec emissions, if that matters) and I got my hands on a set of gauges. The following two states are what I have observed so far:

Car off, resting pressure:
High: 100psi
Low: 85psi

Car on, A/C on (cooling fan engages, as does the compressor clutch):
High: 100psi (essentially no change)
Low: 0psi

I haven't been able to find a similar scenario in my searches, and am not familiar enough with the system to start pulling parts... has anyone seen a similar scenario?

What additional info would be helpful in this diagnoses?
 

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Sounds undercharged to me- compressor is successfully moving refrigerant from low side to high, but it runs out of supply from the low side before it has made a dent in the high side.

I suggest taking it to a shop to have the old refrigerant recovered. Then replace o-rings & valves yourself, vac it out, oil it and charge it. Use a scale and be precise- these compressors cannot tolerate an overcharge. Even a little extra can be an expensive mistake.

It helps to know the ambient temp at the time the pressures are read, but yours are so far off it's pretty clear without that info.

This video may help. It happens to show a Subaru, but Subaru AC (and its operating pressures) are similar to most everything on the road.

 

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Discussion Starter · #3 ·
Thanks for the advice! FYI, it's ~85f @ 50% humidity ATM.

Will look into cost of EVAC for the system and go from there. Luckily Subaru seems to have been thinking ahead in their A/C system capacities... 21-25oz refrigerant is called for, so two full 12oz cans + oil & UV dye should be perfect.

By valves, do you mean the valves at the compressor? My understanding from what I've read so far is that you effectively need to rebuild the compressor itself to get at those... or am I mistaken?

Will most likely just throw a new dryer in at the same time... easy enough if it's already going to be cleared out.
 

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Thanks for the advice! FYI, it's ~85f @ 50% humidity ATM.

Will look into cost of EVAC for the system and go from there. Luckily Subaru seems to have been thinking ahead in their A/C system capacities... 21-25oz refrigerant is called for, so two full 12oz cans + oil & UV dye should be perfect.

By valves, do you mean the valves at the compressor? My understanding from what I've read so far is that you effectively need to rebuild the compressor itself to get at those... or am I mistaken?

Will most likely just throw a new dryer in at the same time... easy enough if it's already going to be cleared out.
No I mean the two schrader valves that you've used to attach your gauge manifold. The seals in them can dry out, but they are modular, cheap and common. Even the tool is still $2 everywhere.

Relevant thread with data, and a link to the how-to thread
 

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Discussion Starter · #5 ·
@rasterman

Follow-up question to your suggestion: if the low pressure side equalizes relatively quickly after the car is turned off, is that a sign that the control valves in the compressor (or possibly the expansion valve) is going as well?

It almost instantly goes from 0psi to ~50psi, and then gradually over about 10min goes up to ~85psi and appears to cap there.
 

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Discussion Starter · #7 ·
Sorry for my obvious ignorance, but by "steady state" do you mean the pressures on both sides of the system will equalize?
 
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