# Thermo King – Unit Performance Field Test

Purpose: This field test determines whether a unit is performing up to standards. To complete the test, prepare the unit, measure the temperature difference of air passing through the evaporator and calculate the unit capacity.
1. Clean evaporator and condenser coils.
2. Check and/or adjust compressor RPM.
3. Check refrigerant charge. It must be full.
4. Check the compressor. It must pass the compressor capacity test.
5. Locate calibrated thermometer sensors in the evaporator inlet and outlet air stream or use return and discharge air sensors.
6. Locate unit CFM. Use TK 2671, TK marketing literature or the Temperature Control System Reference Guide.
7. Stabilize box temperature near 35 F (2 C) or 0 F (-18 C) and measure the temperature change.
8. To determine capacity, use formula: TD x CFM x K = Btuâ€™s.
TD = Evaporator Temperature Difference
CFM = Evaporator Cubic Feet of Air Per Minute
K = Constant based on box temperature
K = 1.24 at 0 F (-18 C)
K = 1.15 at 35 F (2 C)
9. Compare calculated capacity with published capacity. It should be within approximately 5 to 10 percent of specifications.

A unit that can achieve 10 to 15 Evaporator Temperature Difference (TD) has sufficient cooling capacity for most conditions.