IK1900223 ­ Air Conditioning Electrical Diagnostics

Page 1 of 9

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Document
IK1900223
ID:

Availability: ISIS, FleetISIS
Major
ACCESSORIES
System:

Revision: 5
Created:

8/16/2014

Current
Language:

Last
Modified:

5/4/2015

Author:

Kevin
Kochanek

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Title : Air Conditioning Electrical Diagnostics
Applies To : Post 2010 NGV

CHANGE LOG
05/04/2015 - updated steps 14 and 15 and added wiring diagrams
03/26/2015 - updated process flow to include 3 and 4 wire P+T Transducer
12/8/2014 - Formatted article to template standard.
10/28/2014 - Author updated for feedback purposes
9/8/2014 - Updated SRT, special tools and coding.
8/05/2014 - Initial Article Release




DESCRIPTION
This document is supplemental to IK1900228 and addresses sensor and electronic issues.

SYMPTOM(s)
Compressor clutch does not engage.
Possible Causes:
Failed compressor clutch coil
No ignition and accessory voltage at body controller
No A/C request from HVAC control head to body controller (B/C)
No engine running signal at B/C
Engine speed signal to B/C
Low pressure switch input
Freeze probe
A/C high side pressure
Diagnostic Trouble Code(s) & Dashboard Indicator Light(s):
DTC/Light

Description

Not Applicable

Not Applicable

Customer Observations or Concerns: Not Applicable

SPECIAL TOOL(s) / SOFTWARE
Tool Description
Fluke DVOM
Universal

Tool Number

Comments

Instructions

ZTSE4357

Used for checking
electrical connections

Not Applicable

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IK1900223 ­ Air Conditioning Electrical Diagnostics

Page 2 of 9

SERVICE PARTS INFORMATION
Kit Description

Part Number

Quantity
Required

Notes

Not Applicable

Not Applicable

Not Applicable

Not Applicable

Air Conditioning Electrical Diagnostic Steps

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.

When a failed circuit or component is detected, repair as needed and retest for original
problem.

Step Action

Clutch Engagement Requirements:

Decision
Yes: all signals are correct: Leave engine running
and go to step­2.

A. Start engine
B. Turn the A/C Control to NORM, Fan On, and Temp control to coldest setting.

No: Ignition is not check marked: Shut engine off
and then go to IK0800092

C. Start Diamond Logic Builder (DLB).
D. Watch the following DLB signals:
· Ignition
· Accessory_ Signal_ Input
· HVAC_Low_Pressure_Switch
· A/C_ Request
· Engine_Running
· HVAC_ Freeze_ Protect
· HVAC_High_Side_Pressure
1

No: Accessory Signal Input is not check
marked: Shut engine off and then go to
IK0800092

No: HVAC_Low_ Pressure_ Switch is not check
marked:
Shut engine off and then go to step 5.

E. If the High Pressure Transducer has four wires, also watch for the following signal:
∙ BC_RCD_PT_Temp_Signal

Note: The signals must be check marked or have the correct value for the Body Controller to engage
the A/C clutch.

No: A/C_Request is not check marked: Shut
engine off and then go to A/C Control head
diagnostics (IK1900226)

Is Ignition check marked?
Is Accessory_ Signal_ Input check marked?
Is HVAC_Low_ Pressure_ Switch check‐marked?
Is A/C_Request check marked?

No: Engine_Running is not check marked: Shut
engine off and then go to IK0800080

Is Engine_Running check marked?
Is HVAC_ Freeze_Protect value less than 507?

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IK1900223 ­ Air Conditioning Electrical Diagnostics

Step Action

Page 3 of 9

Decision

HVAC High Side Pressure:
A. Start engine, turn the A/C Control to NORM, Fan On, and
Temp control to coldest setting.

Yes: Leave engine running. If unit is equipped
with the four wire transducer go to step 3; if
equipped with three wire transducer go to step 4.

B. Use DLB to monitor HVAC_High_Side_Pressure.
2

C. Use the A/C charging station gauges to monitor high-side pressure.
D. When the gauge pressure is stable, record the gauge value and the DLB value
E. Compare the DLB value to the high-side gauge reading.

No: If unit is equipped with the four wire
transducer go to step 8; if equipped with three
wire transducer go to step 10.

Does HVAC _High_Side_Pressure match the gauge within +/- 10 psi?

Step Action

Temperature Reading Check:
3

Decision

Yes: Go to step 4.

A. Start engine, turn the A/C Control to NORM, Fan On, and Temp control to coldest setting.
B. Use DLB to monitor BC_RCD_PT_Temp_Signal
C. Use the Infrared Thermometer (ZTSE4799) to check the temperature of the High Pressure line near the P+T
transducer.
Is the temperature from IR thermometer and DLB within 15 degrees F?
No: Go to step 14.

Step Action

Decision
Yes: A/C_Clutch is check-marked in DLB and A/C
clutch is engaged:

A/C Clutch Output:

Verify A/C system operates correctly.

A. Start engine

4

B. Turn the A/C Control to NORM, Fan On, and Temp control to coldest setting.

No: A/C_Clutch is check­marked in DLB but A/C
clutch does not engage:

C. Locate A/C Clutch on the DLB signal column.

Stop engine and go to step 12.

Is there a check mark for A/C_Clutch in the value column?

No: A/C_Clutch is not check-marked:

Is the clutch engaged?

Repeat step 1 and step 2. If all values correct and
all other check marks are there, the body
controller has failed.
After repairs are made, reassemble and retest for
operator concern

Step Action
5

Low Pressure Switch Continuity Test:

Decision
Yes: Leave switch harness unplugged and go to
step 6.
No: Switch has failed, repair as needed.

A. Shut engine off.
B. Disconnect the harness from the low pressure switch.

After repairs are made, reassemble unit to run
and
retest for operator concern.

C. Use a DMM to check for continuity across the switch terminals.

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IK1900223 ­ Air Conditioning Electrical Diagnostics

Page 4 of 9

Note: Switch should have continuity with a fully charged system. The system must have the correct charge for
this test to be valid.
Is there continuity across the switch?

Step Action

Decision
Yes: Circuits are good.
Verify steps 4 and 5 were performed correctly
and the correct decisions were made.
Recheck HVAC_Low_ Pressure_ Switch
on DLB.

Low Pressure Switch Diagnostics Key On Voltage Test:
A. Turn ignition Key-On.

6

No: There is no voltage on either terminal in step
B:

B. Use a DMM to measure voltage between each terminal of the low pressure switch harness connector and a
good ground. Note: One terminal should have 10V+/- 1.0V; the other terminal should have near 0V.
Check HVAC Unit Connector (1210) for pushed
back or damaged pins-K and J.
C. Use a DMM to measure voltage between the two terminals of the low pressure switch harness connector.
Voltage should be 10V+/­ 1.0V
Check Body Controller connector J3 (1600) for
pushed back or damaged Pin-B5.
D. Turn Key-Off
Check voltage at B5 with low pressure switch
disconnected and J3 connected. Pin-B5 should
Are the voltages in step B and step C correct?
have 10v +/- 1.0

No: Voltage in step B is correct. Voltage in step C
is low or zero:
Check continuity from connector 1602 Pin-E5 to
both terminals of the low pressure switch
connector. One terminal must have continuity.

Step Action

Decision

Freeze Probe Diagnostics:
7

No: Step-B measurement is out of chart
specifications:

A. Disconnect the freeze probe from the HVAC Unit harness.
B. Measure resistance between freeze probe connector Pin-A and Pin-B. Record the reading and reconnect
the probe to the HVAC harness.
C. Use the temperature probe on the A/C charging station or a digital thermometer to measure cab
temperature. Record the value.

Replace freeze probe.
After repairs are made, reassemble unit to run
and retest.

D. Disconnect the HVAC Unit connector (1210). Turn the ignition key-On.

No: Step-E has less than 9.0V:
Check the following circuit for open or short to
ground:

E. Use DMM to measure voltage between connector 1210 Pin-G and a known good ground. Record the
reading.

Check Body controller connector J3 (1600) PinB13 to freeze probe connector A.

F. Turn Ignition key-Off.

No: Step B measurement is correct, but step-H is
greater than step B by more than 250 ohms:

G. Disconnect body controller connector J3 (1600) and J5 (1602).
H. Measure resistance between connector 1600 Pin-B13 and connector 1602 Pin-E5.

Check the following two circuits for open or high
resistance:

I. Compare measured resistance in step-B, and current temperature in the cab, to Thermistor Cross Reference 1. Body controller connector J3 (1600) Pin­B13 to
freeze probe connector A
Table shown below.
2. Body controller connector J5 (1602) Pin-E5 to
freeze probe connector B.

J. Compare step-B measurement to step-H measurement.
Is step­B measurement correct for the temperature?
Is step-E measurement 10V +/- 1.0?

Are step-B and step F measurements correct for the temperature, and equal +/- 250 ohm?

Thermistor (Freeze Probe) Cross Reference Table
TEMP (C°)

TEMP (F°)

MIN Ω
(kohms)

NOMINAL Ω
(kohms)

MAX Ω
(kohms)

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IK1900223 ­ Air Conditioning Electrical Diagnostics

-15
-10
­5
0
5
10
15
20
25
30

5
14
23
32
41
50
59
68
78
86

35.03
26.65
20.46
15.84
12.30
9.626
7.589
6.025
4.816
3.874

35.67
27.06
20.72
16.00
12.46
9.771
7.722
6.144
4.922
3.968

Page 5 of 9

36.32
27.48
20.98
16.16
12.61
9.918
7.856
6.265
5.030
4.064

Step Action

Decision

Yes: Go to step 9.

No: Step C measures less than 5V:

P+T Transducer VREF and GND Check:

A. Turn ignition Key­On.
B. Disconnect the connector (6201) from the P+T transducer.
8

Check IP/Engine connector (1702) for damaged,
corroded, or pushed back Pin-3.
Check voltage at Pin-E6 of Body Controller
connector­J5.
If 5V exist at Pin-E6: Check the following circuits
for open or high resistance:

C. Measure voltage between harness connector Pin-4 and a good ground. There should be 5 volts at pin 4.
D. Measure the voltage between harness connector Pin­4 and Pin­1. There should be 5 volts.

Circuit A6DB (connector 1602 J5 Pin­E6 to
connector 1702 Pin-3)
Circuit K6DB (connector 1702 Pin-3 to connector
6201 Pin-4)

Are both step C and step D measurements 5V?
No:
step C has 5V, but step D has