AC woes!!!

I have a 2000 Suburban 1500, front and rear ac.....It worked last saturday morning, got in that afternoon, nothing but hot air.

Put my ac manifold gauges on it and the high side is 43 psi and the low side is 135 psi... I know seems backwards but the fittings are 2 different sized and i don't see how they can be switched.

What does this tell someone that knows about A/C, expansion valve bad, compressor bad?

Thanks in advance.

Compresser running and off readings?
Maifold valves off?
High side gauge may be stuck or quick connector may not may be making good connection on high side.
Have you got the adjustable fittings/quick connectors?
MT

On my 1994, I need to press down hard on the high side connector to get an accurate reading.

Sounds like compressor is definitely shot. Are you sure you are reading that right? The blue side is low and red side is high. Take a static reading by just connecting the quick couplers with both valves closed. The only time you need the valves open are to vacuum or charge. Never charge into the high side unless it is under vacuum and engine is off. Need to make sure you have the exact charge back in there and pressure readings alone can't really get you there, can get you close but the only way to know for sure is to weigh the refrigerant in. There should be a sticker under the hood telling you how much it takes.
After a static reading then start the engine and turn AC on. Look to see if compressor clutch is kicked in and take pressure readings, again leaving both valves on your gauge set closed.
Go here, these folks are really good with helping out.
http://acsource.net/acforum/