The Thermo King TriPac Auxiliary Power Unit (APU) is equipped with a number of protection devices to prevent damage to the unit and to the truck’s electrical system.
- Circuit breaker: The TriPac has a circuit breaker that protects the unit from electrical overloads. If the TriPac experiences an overload, the circuit breaker will trip and disconnect the power to the unit.
- Fuses: The TriPac also has a number of fuses that protect individual components of the unit from electrical shorts. If a fuse blows, it should be replaced immediately.
- High-pressure cutout switch: The TriPac’s refrigeration system has a high-pressure cutout switch that protects the system from overpressure. If the system pressure gets too high, the cutout switch will trip and shut down the compressor.
- Low-pressure cutout switch: The TriPac’s refrigeration system also has a low-pressure cutout switch that protects the system from low refrigerant pressure. If the system pressure gets too low, the cutout switch will trip and shut down the compressor.
- Engine overheat protection: The TriPac has an engine overheat protection system that shuts down the engine if it gets too hot.
In addition to these protection devices, the TriPac also has a number of features that help to prevent problems in the first place. For example, the unit has a built-in air filtration system that helps to keep the engine and other components clean. The unit also has a self-diagnostic system that can detect potential problems before they cause a failure.
If you have any questions or concerns about the protection devices on your TriPac APU, please consult the operator’s manual or contact a qualified Thermo King dealer.
High System Pressure Cutout Switch
The High System Pressure Cutout Switch is a normally closed system pressure sensitive switch.
On models manufactured prior to 9/06, it is part of the binary pressure switch, mounted on the receiver-drier, typically near the TriPac condenser. On models manufactured during 9/06 and after, a High Pressure Cutout Switch (HPCO) is located at the receiver/drier.
If the discharge pressure rises above the switch’s opening pressure, the switch opens the circuit to stop the unit and generates an AcS Alarm Code. The opening pressure for the binary switch is 325 psig (2241 kPa). The opening pressure for the HPCO is 400 psig (2758 kPa).
When the discharge pressure falls below the switch’s closing pressure, the switch closes to allow compressor operation. The closing pressure for the binary switch is 230 psig (1586 kPa). The closing pressure for the HPCO is 325 psig (2241 kPa).
Low System Pressure Cutout Switch
The Low System Pressure Cutout Switch is a normally closed pressure sensitive switch.
On models manufactured prior to 9/06, it is part of the binary pressure switch, mounted on the receiver-drier, typically near the TriPac condenser. On models manufactured during 9/06 and after, a Low Pressure Cutout Switch (LPCO) is installed at the evaporator coil.
If the pressure falls below the switch’s opening pressure, the switch opens the circuit to stop the compressor. The opening pressure for the binary switch is 22.5 psig (155 kPa). The opening pressure for the LPCO is 5 psig (34 kPa).
When the pressure rises above the switch’s closing pressure, the switch closes to allow compressor operation. The closing pressure for the binary switch is 40 psig (276 kPa). The closing pressure for the LPCO is 20 psig (138 kPa).
Fuse Protection
The electrical system is protected by a number of fuses (see “Fuses” on page 18). Most of the fuses are located on the interface board shown above, or in the control box near the interface board.
Engine Reset Switch
The engine is protected by a reset switch. When the reset switch opens the engine will shut down. Typical causes for an open engine reset switch are low oil pressure, high water temperature or an engine start failure. The engine reset switch is located on the side of the Interface Board control box enclosure.
