31 Low Pressure Cut Out MP4000

Description

Low Pressure Cut Out 

• If Low pressure switch is mounted. 
• The switch is OPEN. 
• If pressure transducer is mounted. 
• The suction pressure has been measured below 
• -0,27BarR and has not yet increased above 
• +0,38BarR. 
• Indicates: 
• Low refrigerant charge. 
• Refrigeration system restriction at filter drier or expansion valve. 
• Defective low pressure cutout switch. 
• Defective low pressure transmitter. 

Corrective Action 

• Check discharge and suction pressure gauge readings: 
• If refrigerant pressures are low, check for a restriction and leak check the refrigeration system. 
• If refrigerant pressures are high, check for a high refrigerant charge (see below). 
• Check for a restriction: 
• Check for frost on downstream side of the filter drier. 
• Check for high evaporator superheat using supply air sensor temperature readings in Data menu or a frost pattern on expansion valve side of the evaporator coil. A large temperature difference between the left hand and right hand supply air sensors indicates a possible evaporator restriction or incorrect superheat. 
• If Low pressure switch is mounted 
• Check low pressure cutout switch wiring. 
• Measure the voltage across the switch, located at J9 pin 6 and pin 5. 
• - Switch closed (normal) voltage is 0VDC. 
• - Switch open (LPCO) voltage is approx. 12VDC. 
• Replace switch. 
• If pressure transducer is mounted, 
• Measure the transducer supply voltage at J1 pin 8 related to J1 pin 9 (GND). Expects to be approx. 12VDC. 
• Measure the transducer output voltage at J1 pin 7 related to J1 pin 9 (GND). Expects to be above 0,5VDC (0BarR = 0,8VDC)