The Refrigerant Pump-Down Method

What is a refrigerant pump down? A system pump down utilizes a valve and can be automatically done or manually done by a technician. Automatically happens the system is equipped with a pump down solenoid and valve. Automatic refrigerant pump down happens when the system setpoint temperature has been achieved, the solenoid valve will close and the refrigerant is stored on one side of the refrigeration system.

Manually when there is no solenoid valve in the system and the technician closes the liquid line valve manually for the pump down of refrigerant into the condenser. The compressor will pump refrigerant into the condenser and/or receiver, pumping it from the low side of the system.

Manual Refrigerant Pump Down Question: We are in the process of getting estimates to replace our evaporator/blower of a 2 piece unit.

Technicians often pump the refrigerant into a part of the system where it can be sealed off

When asked about the process out of curiosity the HVAC guy told us since the system holds pressure and the refrigerant/condenser is new he will just “park” the refrigerant in the compressor, then cut the line to the evaporator, attach the new one and open the compressor valves to get the system up and running. Is this possible? Can a compressor hold all the refrigerant of an HVAC system?

The Refrigerant Pump-Down Method

Yes, this is in fact, true and it’s called the refrigerant pump-down method. Whenever a new condensing unit is purchased it is pre-charged at the factory with refrigerant. Most are precharged for a line set up to 25 feet. The refrigerant is released by opening two valves, one for the liquid line (liquid line service valve) and the other for the suction line (suction line service valve) - see diagram above for valve details.

That is done all the time by HVAC technicians when they have to open the system. The systems are opened to work on the line set or evaporator coil. If work needs to be done on the condenser then this method will not work. I have done the refrigerant pump-down method many times and it is quite common in HVAC. I would do this the same way as your HVAC guy.

It saves the HVAC contractor time and money and he can pass the savings on to you. It typically takes less than 5 minutes to pump-down the average residential air conditioner or heat pump. He will definitely save time there. Simply closing off a valve in the liquid line and manually turning on the condenser the refrigerant is stored in the condenser to work on the low side of the system.

The alternative is to use a recovery machine to recover all the refrigerant from the system. That will take longer because recovery machines are slow and tedious. Plus, you have to store the refrigerant in a tank. Many contractors try to keep one tank they use for situations like this but some do not.

Refrigerant Cross Contamination

This is important because sometimes these tanks also store refrigerant from a burn-out or a burned up compressor. That means it is possible there could be residual acid in the tank. If that acid gets into your system it could have disastrous consequences for your HVAC system. The alternative to that is for the HVAC contractor to recover the refrigerant. They will then replace it after the job is done with virgin refrigerant.

That costs extra. In addition to the new refrigerant, the contractor has to charge you for he will also likely charge you a disposal fee for disposing of the old refrigerant. So that is why he prefers to do the refrigerant pump-down method versus doing it the alternative way described above.

Easy Process for HVAC Technician

Pump-down solenoid on a commercial chiller

The process of doing this may sound complicated but it is easy for an HVAC technician. Many HVAC technicians perform the refrigerant pump down method. Especially when they are going to open the refrigerant circuit to make a repair. There are two valves at the condenser, one valve for the suction line and one valve for the liquid line. The HVAC technician closes the liquid line valve and turns the air conditioning on. The compressor pumps all the refrigerant into the condenser coils.

The HVAC technician watches his gauges carefully. When the pressure gets to zero he quickly closes the suction line valve. This traps the refrigerant in the condenser and then he turns the compressor off. This saves using refrigerant unnecessarily. This is because the same refrigerant in the system is reused for the new evaporator coil in the air handler.

After the new evaporator coil  is installed the HVAC technician evacuates the new part of the refrigeration system. When completed with the evacuation process opens the valves to allow the refrigerant into the new part of the system.

To make sure the charge is correct he uses his gauges. Using the superheat method or sub-cooling methods he ensures the proper amount of refrigerant is in the system.

Chilled Water Systems and Other Refrigeration Systems

The photo is a solenoid valve for automatic refrigerant pump-down (automatic refrigerant pump-down method). This is on a chiller which uses the valve before it shuts down. The pump-down cycle evacuates the evaporator coil and suction line of any refrigerant.

Same refrigerant pump-down method a residential tech does manually except the chiller does it automatically. Chillers commonly do a pump-down cycle using a solenoid valve before shutting down. This prevents liquid refrigerant from migrating to the compressor while in the off or shut down cycle for the chiller.

All grocery stores have refrigeration systems and these refrigeration systems commonly use the pump down cycle for their systems. It’s a simple control sequence using a liquid line solenoid valve for the process of pumping down.

Refrigerant Pump-Down Method

Technical Resource: Refrigeration and Air Conditioning Technology