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TK 62061-18-IM-EN
Spectrum SPR Valves Setting
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SPRs are set to 2 bar as default from factory, measured in the pressure port close to the valve.
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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.
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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’s functionality (by disconnecting that compartment's temperature sensor or via the
compartment selection menu on the In-cab Control Box), so that only compartment 1 remains functional.
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 (by reconnecting the temperature sensor, if it was disconnected, or via the compartment
selection menu on the In-cab Control Box) and deactivate compartment 1, following the same process as for
compartment 2.
5. Adjust the SPR valve in compartment 2 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.
6. Activate compartment 1 again and check that the suction pressure reading on the road compressor port remains
stable as set during 5-10 min.
7. Stop unit and disconnect pressure gauges.
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