Controller Power, Ground And A/C Switch; Background; Power And Ground Circuit; Possible Failure Modes - New Holland T8010 Manual

Controller Power, Ground And A/C Switch

NOTE: See Schematic Sections 58, 60 and 61.

Background

HVAC Ground
HVAC ground is both a grounding stud at the rear of
the HVAC box and chassis ground at ring terminal
172F through C139-F on wire 178-Bk.

Power and Ground Circuit

Standard Controller
Whenever switched B+ is present, 12V is fed the controller from fuse 47 (30 amp) through C139-R to pin A at the
controller (CCU1).
The controller is grounded from pin F (CCU1) to the HVAC ground stud.
A/C Switch
The controller feeds 5V from pin E (CCU1) through C139-L to the switch at pin 6; grounding pin 6 with the switch
provides the ON request to the controller.
The switch is grounded from pin 5 to chassis at Splice C14.
Pressure Warning Lamp
The controller provides switched ground from pin C on (CCU2) through C139-M to the switch at pin 9 for the
pressure warning lamp.
The lamp is powered at pin 10 with switched B+ from Splice C43.

Possible Failure Modes

1. Fuse 47 or open condition in power or ground to controller.
2. A/C switch failure.
3. Open condition in power or ground to switch or pressure warning lamp.

Controller Power Supply and Ground Test

Steps and Test Point
1. Keyswitch ON. Measure the voltage between pin A
at the controller (CCU1) and chassis ground. Is
12V present?
2. Check fuse no. 47 (30 amp). Is 12V present?
3. Measure resistance from pin F at the controller
(CCU1) to the HVAC ground stud. Less than 1
ohm?
Section 50 - Climate Control - Chapter 1
YES - Go to Step 3.
NO - Go to next Step.
YES - Locate and repair open condition between fuse
47 and pin A at the controller.
NO - Locate and repair open condition from fuse 47 to
switched B+. Go to next Step.
YES - Test the controller. See Standard Controller
Test in this Section.
NO - Locate and repair open condition from pin F to
HVAC ground.
50-1-86
Intermittent Ground
Inter mittent HVAC groun d ca n make r eli abl e
troubleshooting very difficult. The "intermittent"
nature of the problem is further complicated since the
fault can appear to move from component to
component. Early testing for a stable and consistent
ground at the ground bolt and ring terminal 172F can
greatly simplify troubleshooting.
Corrective Actions