It sounds like your compressor is locking up and releasing intermittently. Have it checked by someone familiar with AC systems.

 

It may be overcharged so the high-pressure cutout is activating, or undercharged. Take it to a shop that does AC repair and have them put gauges on it and check/adjust the charge level in the system.

 

I know what is wrong -- your A/C is actually working so well that the coils are frosting up and the A/C is kicking into defrost mode. There is a moisture sensor that controls this, no idea where it is; have that checked as well as coolant pressure.

 

How do you know what is wrong with his car without even seeing it?
There are many reasons why the compressor would be cutting out, it may be normal cycling or not. If it's staying off for 5 minutes that isn't normal.
There is no "moisture sensor", just a thermoswitch in the evaporator that cycles the compressor off when the temp gets too low (close to freezing). This would normally cycle the compressor off for only a few seconds, then it would re-engage. In a properly functioning system this would cause only a momentary rise in air temp at the vents.

 

I know because I had the EXACT same problem on my WRX, and that's the dealership's diagnosis. When the sensor detects that the coil is cold enough to ice up it acually turns off the A/C compressor and turns on the heat, and the heat stays on until it thinks any ice or frost on the A/C coil is gone. The reason it resorts to such drastic measures is that the alternative is a frozen A/C coil which then dumps a bunch of water into the passenger-side footwell after you turn off your car. When this was happening to me, my A/C would cycle off anywhere from 30 seconds to 5 minutes or more. The fix for me was a recharge of the system and a replaced coil.

 

Wow, they actually told you that? Truth is, there is no connection between the AC and heat on a manual HVAC system. The thermosensor measures the temperature of the evaporator core, and cycles the compressor off when the temp approaches freezing, then cycles it back on when the temp goes back up to a safe point. That's all it does. The sensor is connected to a small module which controls the compressor clutch according to the sensor input. The ECU also has control over the clutch and will disengage it at high engine loads and under certain other conditions.
There is a TSB update for some of the 02's which consists of a redesigned thermosensor and module which are designed to reduce the incidence of freezups. That may be what was done on your car. I've got one sitting around that I need to install, one of these days.
Also bear in mind that the car in question here is a 95, so things may be a bit different from our 02's and other recent vintage cars. It's also got some miles on it (presumably) so there may be some age/wear and tear issues that aren't as much of a factor on our newer systems.

 

If the '95 has an R134a system (it should) then I would bet that it is substantially the same as current AC systems.

 

This is the way that the tech explained it: When the A/C detects that it is going to freeze the coil, it essentially turns on the defrost. The heat in a Suby is never off (coolant fluid is always circulating through the heater element) and thus the airflow gets vented like it does when you have defrost on, with both Heat and A/C running at the same time -- however, the A/C clutch has stopped the compressor (that "squeak" sound) and so you effectively get just heat.

All I can tell you is that when the A/C was cycling off for me, the air coming out of the vents was HOT. It may have been related to that TSB; they probably fixed it without telling me exactly why, just like they did the seat rail bolt and the cruise control cable TSBs without letting me know until after the fact.

 

It doesn't work that way. All that happens is the compressor cycles on and off based on the input from the temp probe in the evap core, nothing else happens. Either the tech is handing you a line or he really doesn't know.