What is this?

Saw this device on the freon line at the compressors on a one year old house today. Took the pictures intending to ask about them here. They are wired to the thermostat control wires. Have never seen this before.

At the end of the inspection while talking with the homeowner, they came up. He had mentioned at the start of the inspection that he thought the compressors might be noisy. I told him at the end that I thought they were not noisy at all, that he must be getting used to having them going again now that winter is over.

Anyway he proceeded to mention that the things the Builder added to make them quieter must be working. When I asked him to expand on that, he said that he had originally complained about the down stairs unit being extremely noisy at start up. That the builder had installed the devices to fix it. That they would somehow modulate the freon flow or power flow to happen gradually and reduce the noise and (the builder said) they would actually make the units more efficient.

So, what are these? What do they do? Do they do what the client was told from the efficiency end? He said they had indeed improved the compressor start up noise.

What is this (1).jpg

What is this.jpg

It’s a solenoid valve.
It prevents refrigerant flow after shut down.

It keeps the liquid refrigerant on the high side of the metering device and prevents refrigerant migration to the low side.

This is used when evaporators are located below the condenser in most cases. Prevents overloading the compressor at start up.

No “modulating” here.

In this case the evaporator is in the attic - so 2 plus stories above the compressor.

Is is simply open or closed? I saw that it was a solenoid valve and had explained that it would not directly do anything to the power usage - ie control current somehow.

Would this have an effect on efficiency? Or just the noise. Curious for my own knowledge at this point.

The first generation scroll compressors did not have an anti back flow device. If the solenoid was not installed the compressor would drive backwards on shut down until pressures equalized.

Scroll compressors will run backwards on shut down like Gary pointed out, but the old ones will run backwards even with this valve.

You also do not want to start the compressor against a head of liquid refrigerant if the evap is up high. High stress, high power draw and noise.

Much of this has to do with the type of metering device the equipment uses, length of line set, refrigerant charge, elevations etc…

This thing can be used for several applications to include “pump down”.
One thing is does in every case, is stop the liquid refrigerant flow when the equipment shuts off (for whatever reason…).

Haven’t encountered one of these. Thanks for posting

So if the system is having hard start-up, this would be indicated by excessive noise at start-up? In this case this device would help the noise and presumably the life of the unit, ie easier start-up would seem to logically lead to less wear on the unit?

In thousands of houses this is the first one of these I have seen. Would seem like it would be a good idea for many of them? Am I wrong?

I know one of my units is a scroll and is pretty loud at start up.

It is not something that you should arbitrarily put on the unit.
It is something to do to solve an existing problem.

This application gets way too deep for someone that has less than a unit that just won’t start or has a significant problem starting.

Al units have a hard time starting under a partial load.

A “hard start kit” (start capacitor with potential relay) will take care of most starting issues, and is much cheaper to install.