IK1900226 ­ Air Conditioning Control Head Diagnostics

Page 1 of 9

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Document
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IK1900226
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Revision:

2

Major
System:

ACCESSORIES

Created:

8/18/2014

Current
Language:

English

Last
Modified:

10/28/2014

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Author:

Kevin
Kochanek

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Title : Air Conditioning Control Head Diagnostics
Applies To : Post 2010 NGV

CHANGE LOG
10/28/2014 - Author updated for feedback purposes
10/1/2014 - Updated with new IKnow links.
9/8/2014 - Updated SRT, special tools, and coding.
8/05/2014 - Initial Article Release




DESCRIPTION
This document is supplemental to IK1900228 and addresses Control Head issues.

SYMPTOM:
Incorrect vent temperatures with compressor engaged and correct pressure gauge readings
Inoperable modes or blower speeds

SPECIAL TOOLS:
Tool Description

Tool Number

Fluke DVOM Universal

ZTSE4357

Comments

Instructions

Used for checking electrical connections

Possible Causes:
Active DTC
Actuator/ Doors needs to be recalibrated
No voltage or ground to HVAC Control head
Failed actuator
Mechanical door damage
Blower stuck
Failed LPM
No A/C request from A/C control head to Body Controller

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11/3/2014

IK1900226 ­ Air Conditioning Control Head Diagnostics

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A/C CONTROL HEAD DIAGNOSIS
Note-Body controller will not engage the clutch when A/C related DTCs are active. The following procedures are ONLY
VALID if the A/C system is fully charged and the A/C system checks in IK1900228 were performed.
Note- When a failed circuit or component is detected, repair as needed and retest for original problem.
1
HVAC Module Inspection
A. Visually inspect HVAC module for clogged filters,
obstructed ducts, and wiring disconnected from actuators
and Linear Power Module (LPM).
B. Inspect the 5 Amp and 10 Amp, and 30 Amp HVAC fuses.

Decision
Yes: Repair as needed. If A/C
does not operate correctly, go
to step 2. If A/C now operates
correctly, Diagnostic are
complete.

Are issues detected?
No: Go to step 2.

……
2
Control Head Power
A. Disconnect the harness from the control head.
B. Turn ignition Key-ON.
C. Connect a 12V test light between Pin-A1 and B6 of the
A/C control head harness connector (1200).
D. Connect a 12V test light between Pin-A2 and Pin B6 of
the A/C control head harness connector (1200).

Decision
Yes: Reconnect harness to
control head but do not
reassemble control head to
dash, and then go to step 3.
No: Leave control head
unplugged and go toStep 22.

Does the test light illuminate brightly in both steps C and
step D?
(If using a DMM, both Pin­A1 and Pin­A2 should have 12 V ±
1.5)

…..
3
A/C Request to Body Controller
A. Turn ignition Key-ON, HVAC control switch to NORM,
and blower ON.
B. Open DLB.
C. “Watch” A/C Request in the DLB Signal column.

Decision
Yes: Go to step 4.
No: Go to Step 5 (A/C
Request Diagnostics).

Is the A/C Request box check-marked?

….
4
A/C Operation
A. Start Engine.
B. Turn HVAC control to NORM, Blower ON, and temperature to
coldest setting.
C. Turn blower switch to each speed (1-7) and check for proper
fan operation.
D. Turn mode control to each position and check interior vents for
proper mode door operation. Note: Allow time for interior module
doors to rotate to correct
position.
E. Vary mode control from NORM to MAX A/C and check
recirculation mode (increase in vent air flow)
F. Vary temperature control switch and check vents for change in
air temperature.

Decision
Yes: A/C system
operates correctly.

No, Blower, Mode,
Recirculation, and
Temperature controls do
not function: Replace
HVAC Controller.

No, blower speed does
not function correctly: Go
to Step 6 (Blower
Speed Diagnostics).

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11/3/2014

IK1900226 ­ Air Conditioning Control Head Diagnostics

Does the system operate correctly including fan, mode control,
MAX A/C recirculation, and temperature control?

Page 3 of 9

No: Temperature Control
does not operate
correctly: Go to Step 9
(Blend Door
Diagnostics).
No, mode control switch
does not function
correctly: Go to Step 14
(Mode Control
Diagnostics).
No, recirculation does
not function correctly: Go
to Step 18
(Recirculation Door
Diagnostics).

…..
Step 5: A/C Request Diagnostics
5
A/C Request Diagnostics:
A. Disconnect body controller J3 connector (1600).
B. Turn ignition Key-ON, HVAC control switch to NORM, and
blower­ON.
C. Measure voltage at Pin-A2 of connector 1600.

Decision
Yes: Inspect J3 cavity for
bent pins and verify body
controller has power and
ground.
Note: DLBshould show A/C
Requestchecked if body
controller receives 12V on
connector J3 (1600) Pin A2.

Does Pin­A2 have 12V +/­ 1.5?
After repairs are complete,
reassemble unit and retest
for operator concern.
No: Check the following
circuits for open or high
resistance:
Circuit A77A(connector
1600 Pin-A2 to control
head connector 1200 PinA4.
If circuit is good, control
head has failed.

After repairs are complete,
reassemble unit and retest
for operator concern.

….
Step 6­8: Blower Speed Diagnostics
6
LPM Voltage
A. Turn ignition Key-ON.
B. Disconnect the three wire LPM connector (1220)
C. Use a head lamp to Load test Pin-6 (B+) to a good
ground.
D. Use a head lamp to Load test Pin-6 (B+) to Pin-5.
Does the lamp burn brightly on step C and step D?

Decision
Yes: leave three wire LPM
connector (1220) unplugged
and the Key­On: Go to step
7.
Step C is Dim: Check B+
circuit from Pin-6 back to
battery for high resistance.
After repairs are complete,
reassemble unit and retest
for operator concern.

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11/3/2014

IK1900226 ­ Air Conditioning Control Head Diagnostics

Page 4 of 9

Step C is bright and step D
is Dim: Check the following
circuit for open or high
resistance:
Circuit A75-G (connector
1220 Pin­E to left side dash
mounted dual post ground).
After repairs are complete,
reassemble unit and retest
for operator concern.

…….
7
Control Head Speed Signal
A. Turn blower-ON to highest speed.
B. Measure voltage at Pin-4 to Pin-5.
C. Repeat step 4 for each fan speed.
D. Turn blower off and reconnect the three wire LPM
connector (1220).

Decision
Yes: Leave the Key­On and
go to step 8.
No: Key-Off. Replace control
head.

Do the measured voltages for each speed match the chart?
Dash Switch speed
Off
1 (Lowest)
2
3
4
5
6
7 (Highest)

Control Head Voltage to LPM
0-0.4V
1.4V +/- 0.2
1.8V +/- 0.2
2.4V +/- 0.2
2.75V +/- 0.3
3.35V +/- 0.3
3.9V +/- 0.3
5.0V +/- 0.3

…….
Blower Voltage
8
A. Disconnect the two wire blower connector at the LPM.
B. Turn blower-ON to highest speed.
C. Measure voltage between red lead and black lead.
D. Repeat step C for each fan speed.

Decision
Yes: Replace the blower.
Reassemble unit and retest
for operator concern.

Does the motor voltage match the dash­switch speed?

Dash Switch Position
Off
1 (Lowest)
2
3
4
5
6
7 (Highest)

Motor Voltage
0V
3.85V
4.96 V +/-0.5
6.60 V +/-0.5
7.7 V +/-0.5
9.35 V +/-0.5
10.73 V +/-0.5
12.10V +/-0.5

No: Replace the LPM.
Reassemble unit and retest
for operator concern.

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11/3/2014

IK1900226 ­ Air Conditioning Control Head Diagnostics

Page 5 of 9

Step 9-13: Blend Door Diagnostics
9 Blend Door Recalibration
A. Turn the ignition Key-ON.
B. Turn the A/C blower-ON.
C. Set HVAC selector to Defrost Mode.
D. Remove the fuse box cover and remove the 5 Amp
HVAC fuse (Battery to HVAC Control Head) (ProStar
position is F1-B).
E. Wait approximately 30 seconds then reinstall the fuse.
F. You should hear the doors recalibrate by moving from
one extreme position to the other.

Decision
Yes: Blend door operates
correctly. Reassemble unit to
run and retest for operator
concern.

Note - Do not operate the control head during the
recalibration.
G. Start vehicle and check for correct operation of all