Liquid Line Solenoid - Pump Down

[WyrTwister]

Liquid Line Solenoid - Pump Down


Through out the years , I have come into contact with commercial split systems with a Liquid Line Solenoid .

The controls activated the solenoid , when the thermostat ( or Building Automation System ) was satisfied .

The compressor started to pump down and , best I remember , the compressor shut down on low suction pressure ?

That is the reason this method is used , rather than simply have the ASA turn off the compressor contactor ?

Thanks ,
Wyr
God bless

[ryan1088]

To make sure the compressor starts unloaded.

[WyrTwister]

To make sure the compressor starts unloaded.

So , when the BAS initiates a start , the solenoid is opened and refrigerant inside the compressor starts to flow ?

It flows through the evaporator coil until the refrigerant returns to the suction side of the compressor ( hopefully as a superheated gas) ?

The low pressure device / switch activates when the pressure rises to its set point ?

At this step , the compressor starts ? And it starts in an unloaded state / condition ?

Thanks ,
Wyr
God bless

[ryan1088]

So , when the BAS initiates a start , the solenoid is opened and refrigerant inside the compressor starts to flow ?

It flows through the evaporator coil until the refrigerant returns to the suction side of the compressor ( hopefully as a superheated gas) ?

The low pressure device / switch activates when the pressure rises to its set point ?

At this step , the compressor starts ? And it starts in an unloaded state / condition ?

Thanks ,
Wyr
God bless

Yes, I think you have a good grasp on it. It also helps prevent off cycle refrigerant migration. When the solenoid is de-energized at the end of the call for cooling, the solenoid drops and closes. The compressor continues to pump which "stacks" the refrigerant into the condenser until the low pressure switch opens.

Now this isn't ALWAYS the case. When dealing with BAS systems, you should always refer to your sequence of operation of the controls system, since every programmer makes their own interpretation of how things are supposed to work. I had one where the low pressure switch had to make before it'd send power to the liquid line solenoid.

If you're talking about a newer 410 system with a microchannel coil, then the solenoid isn't a true pumpdown system since there is no area in the condenser for the refrigerant to be stacked.