Thermo King – Low Side Pump Down for Diagnosis

Purpose: To test for internal high to low side leaks and to perform service on the low side without refrigerant loss.
Low Side Pump Down Procedure
1. Install a calibrated gauge manifold.
2. Operate the unit in high speed cool for 10 minutes or more.
3. Front seat the receiver tank outlet valve.
4. Pump down the low side to a 25 inch vacuum.
5. Stop the unit. Low side pressure should remain below a 15 inch vacuum for 2 minutes or more.
If pressure rises:
• to zero and stops – indicates low side refrigerant leak to the atmosphere.
• above zero – indicates refrigerant boiling out of the oil or internal high pressure to low pressure area leaks.
6. Repeat pump down up to 3 times. If after the third attempt, pressure still rises, check the following components:
a. Evaporator side of the 3-way valve.
b. Bypass check valve.
c. Compressor discharge valve plates.
d. Pilot solenoid.
e. Hot gas bypass valve on units with modulation or ETV.

NOTE: Refer to “Internal Seal Points” on page 25 for component locations.

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