Electrical Test; Common Control Potentiometer And Circuit Test Procedure - New Holland T8010 Manual

Electrical Test

NOTE: See Electrical Schematic sections 60 and 61.
Power and Ground Circuit
The two pots are grounded from pin C, through C139-S, to HVAC Ground.
B+ read from the controller varies with the position of the pot: 0.0-3.xV.
Blower Speed: B+ is fed from CJ8-28 through C139H to pin B on the potentiometer.
Temperature Control: B+ is fed from CJ8-29 through C139T to Pin B on the potentiometer.
Mode Door: B+ is fed from CJ8-30 through C139T to Pin B on the potentiometer.
Possible Failure Modes:
1. Control potentiometer failure.
2. Open condition in power or ground to control potentiometer.
3. Controller failure.

Common Control Potentiometer and Circuit Test Procedure

Steps and Test Point
NOTE: If fault codes 120 and 121 display sequentially on the Display, the ground from Pin 18 at the controller
through C139-S to the splice is the likely suspect and should be tested first for an open condition.
1. Keyswitch ON and ATC switch to Auto. Turn the
control pot while observing the Instrument Cluster
display. If the fault code displays - 120 or 121 -
only in cer tain locations, the pot is the likely
suspect.
2. Open the overhead panel. Remove and resistance
test the pot between pins B and C. Resistance
must change smoothly ( 0-10K ohms) as the pot is
turned from full CCW to full CW. Drop outs still
present in certain locations?
3. Reconnect the pot to the harness. Is 0.0-0.3V
present between pin B at the and chassis ground
while turning the control?
4. Measure resistance between pin C at the pot and
pin 18 at the controller. Resistance greater than
11K ohms?
5. Keyswitch OFF. Measure resistance from pin 18 at
controller to HVAC ground. Less than 1 ohm?
6. Is 0.0-3.0V present at pin indicated below at the
controller while turning the appropriate control?
Blower Speed Pot ........................................... CJ8-28
Temperature Control Pot ................................ CJ8-29
Section 50 - Climate Control - Chapter 1
Go to next Step.
YES - Replace the pot.
NO - Go to next Step.
YES - Go to Step 5.
NO - Go to next Step.
YES - Locate open condition and repair between pin C
at the pot through C139-S to the controller at pin 18
NO - Go to next Step.
YES - Go to next Step.
NO - Test the controller. See ATC Controller Tests.
YES - Locate open condition and repair between pin B
at the pot through C139 to the controller.
NO - Test the controller. See ATC Controller Tests.
Blower Speed Pot ........................................... Test 13
Temperature Control Pot................................. Test 12
50-1-46
Corrective Actions