walk in box help

[finest]

I dont do any refrigeration but i was asked a question, i dont have many details but any help would be appreciated. Walk in box with outdoor c/u,R-12,pressure switch operating control cuts in @34#, cuts out@19#, maintains about 42*, cch is good. Problem is when it gets cold outside ( below 20*)box satisfies , pressure never gets above 19# to cut comp. back in. Box temp continues to climb and comp does not come back on until outdoor ambiant goes above 20*, any help would be appreciated and sorry in advance for sketchy details.

[jpsmith1cm]

Install a t-stat and LLSV.

Use pressure control for pumpdown only. Set is quite a bit lower. Only to prevent operation in a vacuum.

She will run.

[crackertech]

Install a t-stat and LLSV.

Use pressure control for pumpdown only. Set is quite a bit lower. Only to prevent operation in a vacuum.

She will run.

Ditto that.

[finest]

Thanks for the quick response, i was thinking along the same exact lines but needed a confirmation. Have a great new year.

[pecmsg]

FYI Starting point for R-12 Cut in / Cut out 36 & 16.

Remember the rules: Refrigerant migrates to the coldest point, Warm Moist Air Migrates to a cool dye enviroment.

With that said:

Refrigerant migrates to the coldest point. CCH is keeping it from condensing to a liquid in the crank case but the receiver / discharge line / condenser are still at ambient. ( Including the cylinders )The LP control senses this. As others have said, T-Stat with LLS valve is the only cure & Reset LP control as a safety only.

[itsamine]

How is the head psi controlled?

[finest]

I havent seen the set up yet, so i dont know how the head pressure is controlled , all the info that i have was related to me by the tech. who set it all up. Ill relay what new info i have and hope it works.

[pecmsg]

Problem is when it gets cold outside ( below 20*)box satisfies , pressure never gets above 19# to cut comp. back in. Box temp continues to climb and comp does not come back on until outdoor ambiant goes above 20*.

And what’s the standing pressure of R-12 @ 20*F?