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R Bedell has you going in the right direction. Total system superheat is what you should be concerning yourself with. That number will tell you what the state of the refigerant is coming back to the compressor. You actually don't need the indoor wet bulb reading to figure superheat. You just need to know the saturation temperature of the refrigerant on the suction side of the system (after the fixed orifice). When the guages are hooked to the system and the unit running in the cooling mode, take the pressure reading off of your low side (blue) gauge. Take a temperature pressure chart and convert that pressure to temperature. Now measure the large line (suction) at the outdoor (condensing) unit. Subtract that temperature reading you got off your temperature pressure chart from the reading you got on the suction line. This is your superheat. One other thing to note is that on a fixed orifice system, superheat fluctuates with indoor temperature, outdoor temperature, and cooling load. There should be a performance table inside your condensing unit that will tell you exactly what your superheat reading should be given your conditions. As far as what you should do for a good temperature reading...to get by cheap but still get a quality reading, I would get a probe type thermometer and tape it directly to the suction line with electrical tape. A few good laps with the tape also creates a small insulation factor to get you a good reading. Sorry this is a bit long, but just wanted to get you going in the right direction. Billy
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