62-11863 4-2
4.1.3 Logic
Supra 950MT units are equipped with an 05G compressor with one unloader for capacity control. The capacity-
controlled cylinders are easily identified by the solenoid, which extends from the side of the cylinder head. When
the solenoid is energized, two cylinders are unloaded (operating with no pressure differential) and absorbed power
decreases. A de-energized solenoid reloads the cylinders. There are two modes of operation for the unloader −
temperature control and suction pressure control.
a. Temperature Control
Operation is similar to the standard microprocessor units, except that additional states are present based on the
number of loaded cylinders. Refer to Figure 4.1 and Figure 4.4.
Unloader: The microprocessor will unload two cylinders by energizing unloader relay UFR, which controls the
unloader solenoid. During truck diesel operation, the compressor is limited to four cylinders whenever a compart-
ment is using electric heat.
b. Suction Pressure Operation
The microprocessor monitors the suction pressure of the refrigeration system and controls the unloader to maintain
a maximum operating pressure based on this value (via a pressure transducer). The unloader is energized during
engine or standby motor start.
4.1.4 Relay Operation
a. ENGINE Mode
Automatic Start:
Run relay is energized.
Diesel/Electric relay (DER) receives input from the motor contactor (N2) and the microprocessor:
• Run/Stop solenoid is activated in RUN position
• Fuel pump is energized
• Voltage supply to standby motor contactor and subsequent motor start is prevented
Glow plugs are energized via GPR relay and the starter solenoid is energized via SSR relay. The engine will crank
for 10 seconds or until engine operation is sensed by the alternator signal (L3). The GPR is de-energized after the
auxiliary input is sensed ON. If engine does not start, a 15 seconds null period will elapse before next start attempt.
Run relay (RR) is kept energized.
Table 4–1 Relay Operation
Mode DER GPR RCR SSR FLR CR
1,2
EHR
1,2
EMR
1,2
HGR
1,2
LSV
1,2
RR
1,2
MHR UFR
950MT
ENGINE OPERATION
Off OOOOOOOOOOOO O
GlowOI IOI or OIOOI I I I I
StartOOI IOIOOI I I I I
Cooling O O I O O I or O I or O I or O I I or O I or O O
Off CycleOO I OOOOOOOOO O
Heating O O I O O I or O I or O I or O I or O I or O I or O I or O I or O
Defrost O O I O O I or O I or O O I or O I or O I or O I or O I or O
STANDBY MOTOR OPERATION
CoolingIOIOOI or OOI or OOI or OI or OOI or O
Off cycleIOIOOOOOOOOOO
HeatingIOIOOI or OI or OI or OI or OI or OI or OII or O
DefrostIOIOOI or OI or OOI or OI or OI or OI or OI
I = Output is ON; O = Output is OFF
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