AIR TRACTOR AT-502A, Maintenance Section

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Air Tractor, Inc. Maintenance Page 33
AT-502A/502B/504 March 14, 2018
B. Clutch Inspection
a) Voltage Check
•
Confirm that the clutch is receiving at a
minimum11.5 V or 23 V for 12 V and 24 V
systems respectively. If voltage is not being
received at the clutch run a diagnostic on the
vehicle electrical system. (Note: perform test with
power applied to coil to fully load the circuit)
•
Pulley or Rotor Spin Check
•
With clutch disengage the pulley should spin
freely with no wobbling or roughness/vibration
b) Air Gap Check
• Air gaps exceeding 0.051” (1.3 mm) can prevent
engagement. This often is noticed after the
clutch and compressor temperature is heated
through normal use.
c) Resistance Check
•
Field coils with internal shorts can be tested by
measuring resistance across the field coil. Resistance
should fall within these values.

12 Volt coil resistance should measure between
2.8
Ω and 4.4 Ω @ room temperature

24 Volt coil resistance should measure between
14
Ω and 18.2 Ω @ room temperature
12 Volts
3.2 Ohms