Basically compressors should not be turned on below 50 degrees exterior ambient temperature. At this 50 degree temperature they can be operated to find out if the “compressor motor” is working, the most expensive component; but how well the air conditioning system is functioning inside the house may yet be unclear.
IMPORTANT: During normal testing procedures a 15 to 20 degree differential is desired; this is the difference between the supply and the return air registers. So if it’s 75 degrees ambient and the supply air is 58 degrees (desired) a 17 degree difference is noted. The system is operating satisfactory and has been properly tested. On the other hand, if it’s 50 degrees ambient, a differential temperature cannot be adequately calibrated and the technician will not know how well the system is operating.
Note: When first starting the air conditioning function, let the unit operate for at least 1/2 an hour. When operating the air conditioning, the air temperature will always be a constant number of degrees, even if you raise or lower the thermostat. The desired constant temperature should be very close to 58 degrees.