Thermal Switch Tests Brush Life Estimate Tools Needed Digital Multimeter Or Equivalent 1 1. Before installation of new brushes, make an inspection of the armature commutator, see Armature Commutator Inspection in Testing and Adjusting. Open Circuits Test 2. Do the steps and procedures for New Brush Installation in Testing and Adjusting. 3. Make the initial (first) inspection of brush wear between 250 smh and 500 smh. The reason for this initial inspection is to see if the brush wear rate is normal and not too fast. The measurement will help make an estimate of the length of brush life to be expected. NOTE : If there is an indication that brush wear is too fast, see Troubleshooting, Problem:
Sparks at the commutator and/or rapid brush wear; for probable causes of this problem. Open Circuit Test 1. Put the digital multimeter Function/Range Switch on the 200 ohm resistance (Ѕ) scale. 4. Inspect all brushes in the motors. Measure and record each brush length (see Specification for each new brush length and minimum brush length). 2. Put one test lead to each side of the thermal switch harness. 5. Estimate expected brush life (hours). Use the shortest measurement from Step 4 and the following Sample Procedure: 3. The resistance must be less than one ohm.
Ground Test Length of new brush ................45.8 mm (1.803 in.) Minimum length of brush...............19 mm (0.75 in.) New brush length [45.8 mm (1.803 in.)] - Minimum brush length [19 mm(0.75 in.)] = Total amount of usable brush wear [26.8 mm(1.055 in.)]. Length of shortest brush at 500 smh is 43.3 mm (1.703 in.). New brush length [45.8 mm (1.803 in.)] - Length of shortest brush at 500 smh [43.3 mm (1.703 in.)] = Amount of brush wear at 500 smh [2.5 mm (.10 in.)]. Amount of brush wear at 500 smh [2.5 mm (.10 in.)] Ц Total amount of usable brush wear [26.8 mm (1.055 in.)] = Portion of brush used at 500 smh (.1). Ground Test 1.
Put the digital multimeter Function/Range Switch on the 20M resistance (Ѕ) scale. Service Meter Hours (smh) at brush wear measurement (500 smh) Ц Portion of brush used (.1) = Approximate total brush life of a new brush (5000 smh). 2. Put one test lead to either of the plug prongs. The other test lead must be grounded to the motor housing. There must be more than one megohm resistance. Approximate total brush life of a new brush (5000smh)PAmount of smh at brush life estimate (500 smh) = Remainder of usable brush life (4500 smh). Power Train Testing And Adjusting 20