Jan 12, 2021
In this short podcast episode, Bryan talks about the strategies we can use to prevent refrigerant migration during the off cycle.
We often see refrigerant migration when the compressor is lower than the evaporator, especially in low-ambient conditions when the refrigerant can condense in the crankcase. When the compressor starts up, you get a violent reaction as the refrigerant boils off and ejects oil. That can wear out the compressor and reduce the lubrication.
Crankcase heaters are some of the most common devices we use when preventing refrigerant migration. These can be of the insertion or belly-band variety. As their name suggests, crankcase heaters keep the crankcase warm during the off cycle to prevent the refrigerant from condensing. However, that isn't a complete solution for stopping flooded starts and other issues.
In the cases of flooded starts, we can use liquid line solenoid valves. These valves close off the liquid line when de-energized (in the off cycle). In many cases, we can use these WITH a crankcase heater for more protection.
We also use pump down solenoids to prevent refrigerant migration. In these cases, the liquid line solenoids will de-energize while the compressor and condenser fan keep running. Then, the system cycles off on a low-pressure switch. If there is any leakage in the valves, the compressor can short-cycle. You can prevent short cycling if you have a pump-out control. However, it is usually a good idea to use a pump down solenoid with a crankcase heater.
We also use hard shutoff (HSO) or non-bleed TXVs in residential HVAC. These function a bit like a liquid line solenoid valve, but you'll also want to use a crankcase heater for added protection.
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