Typically its 1 inch in front of the condensor to get your reading. There are lots of cheap digital thermometers with a wire sensor. I bought one from radio shack for around 8-10 bucks if memory serves. I dangle the lead in front of the condensor to get that reading. Its also nice to stick in the center vent to get a good vent temperature reading.

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Tjohn

82 300 SD
77 450 SL (gone)