How about that - I had the EXACT same problem on my Grey SVX about a year ago......
I found that the A/C compressor clutch was not being activated when the A/C was turned on. The Trinary Pressure Switch was open-circuit, indicating a low refrigerant charge.
It turns out that the refrigerant had leaked from inside the switch itself! The internal seal inside the Trinary Switch had failed, allowing refrigerant to leak out from the body of the switch, where the electrical contact pins are.
It was cheaper for me to replace that entire section of pipe, which includes a new switch. I purchased one from the USA (1stsubaruparts.com).
It is very easy to replace that section of pipe - it comes with new o-rings on each end, so you simply unbolt the fittings at each end, and bolt the new pipe on.
If your system is still running R-12 refrigerant, you will need to convert the system over to R-134a - this involves replacing the receiver / drier unit, and changing the compressor oil.
Jason.
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1992 Charcoal Grey SVX - 165,000km
1992 Ruby Red SVX - 165,000km
....now with sequential VIN numbers!
1986 Holden (Isuzu) Piazza Turbo - 225,000km
1993 Mercedes W140 S500 Coupe - 153,000km
1990 Mercedes W124 300D - 313,000km
EG33 + 4EAT + VTD AWD = SVX
