ROD AS 6E1049 - Caterpillar

Electrical System
Problem 2
The operator compartment has no air flow. The evaporator blower motors do not operate when the fan switch is activated.
Perform the following procedure:
Inspect the circuit breaker or inspect the fuses for an open circuit.
Check for the proper function of the control panel at several speed settings. The evaporator blower motor must run at each setting. The evaporator blower motor should be operating in the cold mode and in the heating mode.
Illustration 1 g03810624
Blower control switch for analog signal is on the left side.
Illustration 2 g03810641
Electrical Connector Pins for Control Panel
If necessary, make repairs or replace components.
Check for the proper function of the control panel at various speed settings using the following procedure.Perform this test with the key in the ON position. Use a 5P-7277 Voltage Tester or use a 257-9140 Digital Multimeter and connect the negative probe to the pin 6 wire on the control panel using a 7X-1710 Multimeter Probe 7X-1710 wire assembly or equivalent. Check the supply voltage first by connecting the positive probe to the pin 3 wire using a 7X-1710 Multimeter Probe wire assembly or equivalent. If the system voltage is not measured, do not perform any of the other tests below until that is repaired. Select the blower switch and connect the positive probe to pin 4 using a 7X-1710 Multimeter Probe wire assembly or equivalent and record the voltage. For a properly working control panel, the voltage should be the same as the system voltage. Repeat for all speeds. Replace the panel if any of the voltages are not present during the test.If the panel passes the test, then refer to the machine electrical schematic and check for voltage to the motor and resistor.Test Procedure for Testing Electrical Components in the Air Conditioning System
The air conditioning systems on Cat® machines use pressure switches to protect the air conditioning system. Some air conditioning systems on Cat machines use pressure switches and on delay timer assembly for the refrigerant compressor to protect the air conditioning system. Arc suppressors protect other electrical components in the air conditioning system. Arc suppressors are applied to discharge electrical inductance when the compressor disengages. Failure of the arc suppressor can affect the reliability of the pressure switch. Failure of the arc suppressor may cause failure of the pressure switch.The following procedures are for the testing of the on delay timer assembly, pressure switches, and components of the arc suppressor.
Table 1
Required Tools
Part Number Part Description
257-9140 Digital Multimeter (Fluke 87) Pressure Switch Tests
Test Procedure for 149-6371 AC Low-Pressure Switch and 355-3148 AC Hi Pressure Switch .
Pressure switches are used to protect the compressor for the air conditioning. The switches are used to detect when pressure is either high or low. The output of the switches is monitored by the Implement ECM.
Illustration 3 g06012958
Electrical connections for the low and high-pressure sensors for the monitoring the HVAC system.
Use the following procedures when testing a "SUSPECTED FAULTY" pressure switch:
Table 2
Follow The Process Below When Troubleshooting A Suspected Faulty Switch
1.