MacDon M155, Operator'S Manual

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MAINTENANCE AND SERVICING
3. Reattach drain hoses to drain tubes and secure with
hose clamps (A).
Figure 5.48: HVAC System
Air Conditioning (A/C) Compressor
The compressor is protected from excessively low suction and high discharge pressures by two switches that
shut down the compressor to prevent damage to the system. These switches do not require regular servicing or
maintenance. Contact your MacDon Dealer if you suspect a problem with the switches.
• The low pressure switch is normally closed when there is suf fi cient refrigerant in the system and the pressure is
above 34 psi (234 kPa). The system remains pressurized at about 60–70 psi (414–483 kPa) with the compressor
off. When the A/C system is turned on, the compressor starts because the system pressure is above 34 psi (234
kPa). As the system gets colder, the suction pressure (low side) drops. At 3.5–12.5 psi (24–86 kPa) (for 2014 and
prior: 2–8 psi [14–55 kPa]) , the switch opens and shuts down the compressor. When the pressure rises above
15–25 psi (103–172 kPa), the switch closes and the compressor restarts. The low pressure switch is located at
the outlet of the evaporator (under cab in the A/C box).
• The high pressure switch is normally closed when there is suf fi cient refrigerant in the system. The system
remains pressurized at about 60–70 psi (414–483 kPa) with the compressor off. If the pressure exceeds
360–380 psi (2482–2620 kPa) during operation, the valve opens. It will close when pressure falls below
220–280 psi (1517–1931 kPa). The high pressure switch is located on the receiver drier (right cab-forward
frame rail, behind the fuse panel).
If the compressor cycles rapidly due to rapid pressure changes, the cab display module (CDM) displays a warning
CHECK A/C SYSTE”. Contact your Dealer.
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