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SPR default factory setting
SPRs are set to 2 bar as default from factory, measured in the pressure port close to the valve.
Recommended SPR valve settings depending on the customer application
To maximise unit pull-down and performance both in cool and heating modes, SPR valves must be adjusted to the following values:
•
Warm countries: 2.2 bar (measured at road compressor suction port)
•
Cool countries: 2.7 bar (measured at road compressor suction port
These settings allow the unit to operate properly in fresh/fresh and fresh/frozen conditions. However, for fresh/frozen applications, heat load in the fresh compartment should
represent at most 20% of the maximum full unit capacity, as per ATP certificate at 0ºC / -20ºC conditions.
If the fresh compartment heat load is greater than 20% of full unit capacity, the SPR valve located in the fresh compartment shall be adjusted to a 1.3 barg pressure reading,
measured in the pressure port close to the valve. This is to ensure that the evaporator in the frozen compartment can deliver cooling capacity when the evaporator in the fresh
compartment is running. This change leaves the unit asymmetrically configured, so fresh/frozen compartments cannot be swapped and have the same performance. In
addition, the pull-down process does not occur symmetrically in both evaporators either due to the unbalanced pressure setting of the SPR valves.
In this case, if unit symmetry and reversibility must be maintained, both SPR valves shall be set to 1.3 barg, measured in the pressure port close to the valve. However, the
impact on unit pull-down time and performance is significant.
SPR valve adjustment procedure
Before adjusting the SPR valves, the unit must be fully installed on the vehicle and have the appropriate oil and refrigerant charge (the thermostatic expansion valve does not
need to be adjusted). The process described assumes that the ambient temperature is high enough to have system pressures (discharge and suction) under normal operating
conditions. However, if system pressures are too low due to low ambient temperature conditions (< 0 ºC), the same process could be followed by running the unit on heating
mode and letting the compartment temperature rise to an acceptable level (> 15 ºC).
1. Connect the pressure gauges to the road compressor ports. Start the unit in cooling on road mode (2000 - 2400 compressor rpm).
2. Stop compartment 2 operation (this could be done by disconnecting the temperature sensor of this compartment), so only compartment 1 is running.
3. Adjust the SPR valve in compartment 1 until the suction pressure reading on the road compressor port matches the recommended value for the application. Leave the
unit running for 10-15 min to check that the pressure reading is stable.
4. Activate compartment 2 (reconnect temperature sensor, if disconnected) and deactivate compartment 1, as described for compartment 2.
(Rev. 4, 01/15)
Spectrum SPR Valves Setting
Eng
58
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