14
IF SHORT CYCLING ON THE HEAD PRESSURE CONROL AT THE END OF THE DEFROST, THE
SYSTEM IS OVERCHARGED.
IF THE PRELIMINARY CHARGE IS USED, YOU WILL NOT SEE AN OVERCHARGE.
IF ANY SHORT CLYCING IS OBSERVED AT THE BEGINNING OF THE DEFROST CYCLE. ADD 1/2
INCRIMENTS OF R-449A UNTIL THE SHORT CYCLING GOES AWAY. ALLOW THE SYSTEM TO
PULL BACK DOWN TO TARGET ROOM TEMPERATURE, THEN TEST SYSTEM AGAIN WITH A
MANUAL DEFROST. REPEAT UNTIL NO SHORT CYCLING IS SEEN.
NOTE: DO NOT BLAME SHORT CYCLING ON THE CHARGE UNTIL THE LOW PRESSURE
SETPOINTS ABOVE HAVE BEEN CONFIRMED.
8. Since the Master Control Refrigeration System is designed to operate at a floating head
pressure, low head pressure may be seen at low amblent condition. For example, at a box
temperature of –10
o
F and an outside ambient temperature of 50
o
F, the suction pressure should
be at the neiborhood of 8 to 13 PSIG, the head pressure should be at the neiborhood of 130-155
PSIG.
Note: Do not overcharge the system!
Table 6. Preliminary Refrigerant Charges by Compressor/Line Size/Length
Line Size 1/2 5/8 5/8 3/8
Length ZF13 ZF15 ZF18 ZS11
5 3.8 5.9 5.9 3.5
10 4.1 5.5 6.5 3.6
15 4.5 6.0 7.0 3.8
20 4.8 6.6 7.5 4.0
25 5.1 7.1 8.1 4.2
30 5.5 7.7 8.6 4.4
50 6.8 9.8 10.8 5.1
75 8.5 12.5 13.5 6.0
Line Size 5/8 5/8 5/8 3/8
Length ZF13 ZF15 ZF18 ZS11
100 14.3 15.2 16.2 6.9
150 19.7 20.6 21.6 8.7
9. Check operating pressures while charging and on initial pulldown to prevent damage if
problem occurs.
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