Thermo King – Low Side Pump Down – TherMax Units

Purpose: To test for internal high to low side leaks and to perform low side service without refrigerant loss.
Low Side Pump Down Procedure
1. Install a calibrated gauge manifold.
2. Run the unit in cool 10 minutes or more.
3. Front seat the receiver tank outlet valve.
4. When the compound gauge reaches 20 to 25 inches of vacuum, stop the unit.
5. Observe the low pressure gauge. It should remain below a 15 inch vacuum 2 minutes or more.
If pressure rises:
a. To zero and stops: Low side refrigerant leak to the atmosphere.
b. Above zero: Refrigerant boiling out of the oil or internal high pressure to low pressure area leaks. Check the
• Evaporator side of the 3-way valve
• TherMax solenoid
• Discharge valve plates
• Pilot solenoid.
6. Use a process of elimination to identify an internal leak. Perform a compressor pump down to determine valve plate and pilot solenoid condition.
7. The following services can be performed with the low side pumped down and a slight positive pressure established:
• Add or remove refrigerant oil
• Clean expansion valve screen
• Change expansion valve
• Service the throttle valve
• Replace the suction pressure regulator
• Replace drier.

Removing the Compressor or Compressor Heads
1. Pump down the low side to a 15 to 20 inch vacuum.
2. Stop the unit.
3. Immediately front seat the discharge service valve.
4. Balance pressures through the manifold. Add additional pressure from the discharge service valve or RTOV if necessary to establish 1 to 2 psig.

WARNING: Front seat the suction service valve. DO NOT start the unit with the discharge service valve front seated.

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