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How WhisperKOOL’s Pump Down Systems Work

How WhisperKOOL’s Pump Down Systems Work

Welcome to the WhisperKOOL blog. Our focus is on education and product information for our customers, our distributors, and technicians who use our products. It’s our goal to establish realistic expectations of what our products can do and how they work. One of the ways in which WhisperKOOL wine cellar cooling units differ from many other types of HVAC units is that our units employ a “pump down” system.

In the following post, we’ll explain the particulars of pump down systems. We hope this information will help technicians more easily install and repair WhisperKOOL cooling units.

What is a Pump Down System?


Pump down systems have a solenoid valve in the liquid line. This solenoid closes once the temperature reaches the prearranged set point. However, the compressor continues to pump refrigerant into the receiver and/or condenser coil, removing it from the low side of the system. The compressor cuts out once the low-pressure switch registers a predetermined pressure. (This setting is directly related to the type of refrigerant being used in the system.)

When the controller calls for cooling, the solenoid in the liquid line opens. Refrigerant moves into the low side of the system due to the pressure differential between the high side and the low side. When the low-pressure switch reaches a predetermined “cut-in” set point, the compressor will start. As before, the cut-in pressure correlates to the type of refrigerant being used. The entire process is automatic.

The purpose of a pump down system is to prevent liquid refrigerant from “migrating” back into the compressor during an off-cycle. This prevents catastrophic damage to the compressor when the system starts up.

How do WhisperKOOL Cooling Systems work? 

We’ve prepared a short video about how the pump down system works in our WhisperKOOL units. Please click below to view it:


With a WhisperKOOL cooling unit, no wiring is required between the condensing and evaporator units. When the thermostat calls for cooling, the solenoid valve on the liquid line in the evaporator unit opens. Refrigerant begins to flow and the cooling cycle begins. When the cellar has cooled to the desired temperature, the solenoid valve closes and refrigerant flow to the evaporator stops. The compressor continues to operate until most of the refrigerant has been pumped into the condenser coil and receiver. The low-pressure switch’s cut-out pressure is 15 psi. The cut-in pressure is 25 psi.

Charging WhisperKOOL Systems

We at WhisperKOOL strive to make the installation process as easy as possible for the installing technician. One thing we offer is a split system pre-weigh-in charge list. This document comes with every WhisperKOOL split system. It shows how much refrigerant will be needed to charge the system based on the line set length. This charge amount will help the technician complete 90% of the charging process. However, they will still need to top off the system with refrigerant vapor.

Charging must be performed by a licensed HVAC-R technician. If you need help locating one in your area, please give us a call at 1 (800) 343-9463.

For more informative posts like these, please stay tuned to our blog. And don’t forget to check out our website for the latest in wine cellar cooling solutions. Thank you for being a WhisperKOOL customer!

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