Refrigeration System; Description; Defrost Cycle - Hussmann ARL Installation And Operation Manual

REFRIGERATION SYSTEM

Description

All upright merchandisers are equipped with a hermetic or semi-hermetic compressor. The condenser is fin
and tube construction. The air is taken in at the front of the cabinet through the lower grill and discharged
out by the back of the cabinet.
A crankcase pressure regulating valve is utilized on some low temperature models. The purpose of this
valve is to limit the suction pressure AT THE COMPRESSOR during initial cabinet start-up and start-up
after a defrost cycle. IT DOES NOT REGULATE EVAPORATED PRESSURE. The valve is set for a
maximum of 15 pounds of crankcase pressure. In order to check this setting the pressure at the inlet or
evaporator side of the valve must be greater than 15 pounds. Manually initiate a defrost cycle by rotating
the timer dial clockwise until the refrigeration cycle terminates. Install service gauge on the suction service
valve. Observe the pressure on the gauge as the cabinet comes off the defrost cycle. The needle should drop
to valve setting and hold steady. This setting should be a maximum of 15 pounds.
A high pressure limit switch is utilized on all low temperature models. The purpose of this switch is to limit
the discharge pressure of the compressor. This switch will automatically cut off the compressor energy
when the system has too high pressure and start-up the compressor again when the pressure decreases. This
pressure switch is a safety device and will not function during normal case operation. DO NOT remove it
from the system.
Cooling is accomplished by forced air circulation through a finned coil, located in the top of the cabinet.
Air is drawn in at the back of the refrigerated area, and forced through the coil and down the front of the
cabinet.
Defrost Cycle (Low Temperature Models)
The evaporator fin coil is defrosted twice a day for approximately 20 minutes by an electric defrost heater
located on the under side of the coil and secured in place with stainless steel retainer clips.
The defrost cycle is initiated by a time clock located behind the condensing unit and terminated by Defrost
Termination/Fan Delay Switch located on the suction line just before the accumulator. This control not
only terminates the defrost cycle, but delays the fan start-up after the defrost cycle to prevent water from
being blown into the product area. (Note at initial start-up of the cabinet, the evaporator fan will not operate
due to the function of this control. Allow approximately 10 minutes for the control to close).