Master Bilt DD-26 - Operation Conditions and Pressures; Trouble Shooting; Service Instructions

9
OPERATION CONDITIONS AND PRESSURES
With room ambient temperature of +80
o
F and cold cabinet (unit cycling on control):
DD-66 & DD-88 with R-404a
Suction pressure – 6 to 8 psig.
Head pressure – 240 to 260 psig.
If room ambient is low, 60
o
F or lower, then the suction pressure could be as low as 4 psig. Temporary block the
condenser coil to raise head pressure to 240 psig in order to verify proper charge and a suction pressure of 6psig to
8 psig. Remove blockage after pressure check.
DD-26 & DD-46 with R-134a
Suctions pressure –5 to –8 inches vacuum
Head pressure 105 to 110 psig
If room abient is below 70
o
F temporarily block the condenser coil to raise the head pressure to 105 psig and
recheck suction pressure. Add R-134a if suction pressure is lower than –8 inches of vacuum.
SERVICE INSTRUCTIONS (Trouble Shooting Guide)
1. High head pressure and high back
pressure:
A. Condenser coil clogged or
restricted.
B. Condenser fan motor defective.
C. Air in the system.
D. Refrigeration overcharge.
2. Low back pressure and low head pressure:
A. Capillary tube restriction.
B. Refrigerant undercharged.
C. Leak in system.
D. Moisture in system.
3. Pressures normal – cabinet warm:
A. Refrigerant undercharged.
B. Thermostat set too warm.
4. Compressor starts and runs – but cycles
on overload:
A. Low voltage.
B. Overload protector defective.
C. High head pressure (see#1).
5. Compressor will not start – hums, but
cycles on overload:
A. Low voltage.
B. Relay defective.
C. Overload defective.
D. High head pressure (see #1).
6. Cabinet sweating:
A. High ambient humidity.
7. Special service situations
If moisture or liquid is observed around or under a Master-Bilt cabinet, an immediate investigation should be made
by qualified personnel to determine the source of moisture or liquid. The investigation made should determine if
the cabinet is malfunctioning or if there is a simple housekeeping problem.
Moisture or liquid around or under a cabinet is a potential slip/fall hazard for persons walking by or working
in the general area of the cabinet.
Any cabinet malfunction or housekeeping problem that creates a slip/fall hazard around or under a cabinet
should be corrected immediately.