Specifications

22
The recommended charging procedures are:
(1) Charge the system by weighing exact amount of refrigerant specified by Master-Bilt for the unit. Or,
(2) Charge 50% of the liquid receiver (if provided) rated holding capacity. Let the system run through the pull
down period until room temperature is closely reached, then gradually add refrigerant until actual superheat
“SUPH” on board is approaching superheat setpoint “SHSP”. Bubbles may be seen in the sight glass.
(3) In a reverse cycle defrost system, there may not be a liquid receiver. Charge the system the working amount
of refrigerant calculated above. Let the system run through the pull down period until room temperature is
closely reached. Then gradually add refrigerant until actual superheat “SUPH” on board is approaching
superheat setpoint “SHSP”. Bubbles may be seen in the sight glass.
How to diagnose an overcharged system:
An overcharged system will not operate properly.
• First, be sure that system is not leaking
• Compressor may be short cycling
• Frost building up on compressor suction section, suction filter or service valve
• Low superheat alarm appears on the controller display constantly
• Head pressure cut-out during defrsot for a reverse cycle defrost system
Solution:
Taking some refrigerant out of the system until on-board actual superheat “SUPH” is observed approaching
superheat setpoint “SHSP”.
Technical Notes
• With the optional alarm relay the external temperature and alarm indicator should be connected to “C”
(common) and “NC” (normal close) terminals. The alarm does not indicate what causes the alarm. To find
out what has caused the alarm, check the onboard four-digit display for alarm codes and refer to the
diagnosis chart for corrective action. Thermostat wiring can be used for connection.
• Defrost termination set point (DTSP) can be also set up to 80
o
F. When setting the defrost termination
temperature, make sure that the frost is free after each defrost. Also make adjustments to the maximum
defrost duration when necessary.
• The superheat of each application can be set by the customer. Superheat 10-15
o
F is recommended for
winter operation, superheat 5-10
o
F for summer.
• Always clear the “LOSH”, “HITA” and “LOTA” alarms after corrective action is taken. The sensor and
communication alarms cannot be cleared unless they are corrected.
• Cat5/e communication cable should be rated 300 V 80
o
C or higher. If the wire is rated lower than 300 V, a
separate conduit must be used for communication cables.
• Follow the instructions in the Master-Bilt Condensing Unit and Refrigeration System Installation & Operation
Manual to perform the final check up before charging and starting up the system. Always refer to this service
manual, make sure all steps are understood. Don’t hesitate to call Master-Bilt Customer Service Department
at 800-684-8988 for technical assistance.