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View Full Version : Walk in freezer with no LLS



eskimo joe
12-01-2002, 05:33 PM
I WENT TO SERVICE A WALK IN FREEZEER THAT WAS TRIPPING
THE BREAKER EVERY COUPLE OF DAYS. I NOTICED THE SYSTEM
HAS NO LIQUID LINE SOLENOID THE UNIT IS CYCLING OFF THE
PRESURE DIFFERENTIAL SWITCH WHICH IS CONTRLLED BY THE
BOXES THERMOSTAT. WHAT PROBLEMS IF ANY WILL THIS CAUSE
I WAS TAUGHT THAT THE SYSTEM SHOULD BE PUMPED DOWN
BUT OBVIOUSLY THIS WON'T HAPPEN WITHOUT A LLS. THANKS.

frank
12-01-2002, 06:12 PM
Does the system have electric defrost?. With a full evaporator during defrost the suction pressures will be extemely high when the compressor kicks in and may be the cause of the breaker tripping due to excessive current draw.

subzero*psia
12-01-2002, 10:02 PM
Personally, I would install a LLS wired in series with the t-stat on its own circuit, and wire the low pressure switch to the condensing unit on a separate circuit... setting the cut-in and cut-out just for the pump down.

Having the t-stat wired in series with the LPS is redundant. The system probably was originally wired without a t-stat and was controlled strictly by pressure. My personal opinion of having a pressure switch as the main control is that they are only good on fairly constant loads. If you have any infiltration or rapid door opening, a pressure control will cause short cycling... just like you are seeing now. ;)

Gibson
13-01-2002, 07:25 AM
A "new" walk in? I agree with frank and subzero. Install the lls and thermostat. But what is the condensing unit, defrost heaters FLA and breaker size?

subzero*psia
13-01-2002, 03:56 PM
Good Show Gibson!! :D

That had totally slipped my mind!

tom king
07-05-2002, 06:35 PM
Frank & Dean you are so right!
You must have a liq. sol. vlv. wired in series with the room t'stat and defrost timer for pumpdown on a walk-in freezer. Otherwise, the high back pressure on start-up after a defrost will cause the compressor to run outside its designed temperature range and the extremely high back pressure will cause such a load on the compressor that the amps drawn could trip the circuit breaker. Not to mention, the wear, reducing the compressor life.