TM 9-4120-371-14
a. Inspection
(1)
Inspect for evidence of leaks, kinked, or otherwise damaged capillary line, and loose or missing
mounting hardware.
(2) Check thermal bulb to see that it is securely clamped to the suction line.
(3)
If a leak is suspected or indicated, test per paragraph 5-9.
b. Test
(1)
Perform a refrigerant pressure check on unit in accordance with paragraph 5-12. Leave gages or
service manifold attached.
(2) Unwrap insulation tubing from compressor suction line so that sensing bulb and an adjacent
section of the suction line is exposed.
(3) Attach an accurate thermometer to an exposed surface to suction line adjacent to the sensing
bulb; use a small gob of thermal mastic, to improve conductivity.
(4)
Check that service valve and gage connection to low (suction) side are open. Note pressure
indicated on gage and temperature indicated on thermometer.
(5) Set the Temperature control thermostat knob to full INCREASE (clockwise). Start the air
conditioner in COOL mode. Note that suction pressure drops to 58 + 2 psig (4.0 + 0.2 kg/cm2). Allow
compressor to run for at least 20 minutes. If pressure is not within above limits, test operation of pressure
regulating valve (para 524) before proceeding with quench valve test.
NOTE
Except in a very hot climate, with room air temperature above 90F (32.2C), the
refrigeration system will be in a bypass cycle with a maximum volume of hot discharge
vapor being recirculated back to suction side of compressor through pressure regulator
valve and quench valve.
(6) Observe that temperature indicated remains stable for a minimum of two minutes, then find
saturation temperature for pressure indicated on gage, using table 51 . For example: The saturation
temperature for a refrigerant pressure of 69 psig (4.85 kg/cm2) is 40F(4.4C).
(7) Compare the saturation temperature with indicated temperature. The indicated temperature should
be 25 + 5F (13.9 + 2.2C) higher than the saturation temperature. For example: With a 40 saturation
temperature, the thermometer should read 65 + 5F. If indicated temperature is not within above limits, quench
valve is not functioning properly and should be adjusted:
NOTE
If valve does not need adjustment, skip (8) below.
*(8) If the superheat setting is not within the limits shown above, adjust the liquid quench expansion
valve as follows:
(a) Remove the hexagonal seal cap from the side of the power assembly.
(b) Turn the adjusting stem two complete turns to change the superheat setting by 1F (0.55C).
Turn the stem clockwise to increase superheat span; counter clockwise to decrease it. Do not change more
than two full turns at one time, then wait at least 2 minutes for temperature to stabilize and recheck pressure
and temperature before further adjustment. If valve cannot be properly adjusted, replace the valve.
*Effective for Keco Model F18T-2S and A.R.E. Model CVP-20-5/608.
5-35
