Tenney BTS - Page 12

TENNEY ENVIRONMENTAL
overheating of the compressor and the discharge gas.
-
)
A high pressure cut-in sensor monitors the pressure inside the low stage compressor
and will activate the Load Limit Switch 4PS when the low stage discharge pressure reaches
280 PSIG. This will energize the Artificial Loading solenoid
14SOL which will inject refrigerant
into the suction side of the system as described above. Switch 4PS prevents the compressor
from cycling on and off in response to signals from the high pressure cut-out switch. 4PS will
open when pressure falls to 240 PSIG.
For more detailed information on a cascade system, please reference the section entitled
"Servicing Cascade Refrigeration Systems".
REFRIGERAT~N SYSTEM SAFETY DEVICES
The refrigeration system is provided with several safety devices that stop the compressor(s)
from ~nning if conditions exceed preset limits. In a cascade system both the low stage and the
high stage include these safety devices. With a low limit condition the
HI-LO Pressure Cutout
Switch 1 PS (and
2PS for cascade) will continue to automatically reset until sufficient pressure
develops. With a high limit condition you must manuallv reset
IPS (or 2PS). If the compressor
continues to trip off have the system checked by
a qualified refrigeration system mechanic.
The possible causes of a high or low limit cutout are as follows: NOTE:
The HI-LO Pressure
Cutout Switch does not apply to the Models BTS. BTC.
T6S, and T6C.
High Pressure Cutout (1 PS, 2PS) - - Opens if a preset compressor discharge pressure
'- .)
is exceeded. Probable cause for high stage cut-out is insufficient cooling water (water
cooled systems) or restricted air flow (air cooled systems). Probable cause for low stage
cutout is a malfunction of the high stage system.
IPSRPS are typically set at 300 PSIG.
Low Pressure Cutout
(1 PS, 2PS) - - Opens if the compressor suction pressure falls
below a preset value. Probable causes are a loss of refrigerant (either stage) or restricted
air flow across the evaporator (low stage).
1 PSl2PS are typically set at 6 inches of vacuum.
Motor Overload - - Opens if the motor windings exceed a preset temperature. Probable
causes are insufficient flow across the motor due to a refrigerant loss or a failure of the
liquid injection valve provided for suction gas cooling. The motor overload is installed
directly in the motor windings and will automatically reset and restart the compressor after
the motor has cooled.