You know when you are taking the temp of the suction line and indoor/outdoor dry bulb temp. Are non-contact therm ok? I was looking at these.

http://www.harborfreight.com/cpi/cta...emnumber=93984

http://www.harborfreight.com/cpi/cta...emnumber=95382

The probe thermometer seems appropriate. But i've mainly seen people use the thermometers that have the wire that you can put anywhere. Like wrap it around the pipe and so on.