IK1900228 - 2010 and Newer Vehicle Air Conditioning Diagnostics (Start Here)

Page 4 of 7

Were any issues found?

Step Action

Decision

Diagnostic Trouble Codes:
3

Yes: Go to FAULT CODES in
IK1900207

Check for A/C related DTC’s:
Are any A/C related DTC’s found?
No: Go to step 4.

Step Action
4

Decision

Static Pressure:
NOTE: Have the engine OFF and A/C system at ambient
temperature when measuring static pressure.If the engine has been
run recently, allow the vehicle to sit for a minimum of one hour to
allow system pressures and temperatures to stabilize.

Yes: Go to step 5.
No: Go to Air Conditioning
Mechanical Pressures
Diagnostics IK1900225

1. Inspect high and low side Schrader valves for presence of dye
and pooling of oil in valve.
2. Connect gauges to the A/C system and record static pressure
readings.
3. Use a temperature probe to determine the ambient temperature
within 1 or 2 degrees. Record the measured temperature.
4. Locate the ambient temperature on the chart below and
compare the vehicle’s static pressure to the chart pressure.
Temp °F Temp °C R134A PSIG
40 °F

4.4 °C

35

45 °F

7.2 °C

40

50 °F

10.0 °C

45

55 °F

12.8 °C

51

60 °F

15.6 °C

57

65 °F
70 °F

18.3 °C
21.1 °C

64
71

75 °F

23.9 °C

78

80 °F

26.6 °C

86

85 °F

29.4 °C

95

90 °F

32.2 °C

104

95 °F

35.0 °C

113

100 °F

37.7 °C

124

105 °F

40.5 °C

134

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IK1900228 - 2010 and Newer Vehicle Air Conditioning Diagnostics (Start Here)

110 °F

43.3 °C

Page 5 of 7

146

Are the A/C pressures in spec?

Step Action

Decision
Yes: Go to step 6.

Compressor Engagement:
5

Start engine. Turn the A/C on. Verify compressor engagement.
No: Go to Air Conditioning
Electrical Diagnostics
IK1900223

Does the compressor engage?

Step Action
6

Decision

Performance Test:
Check the System Performance by performing the following steps:
A. Park the vehicle so there is no solar loading and no wind.
B. Position a thermometer approximately 30 to 60 cm (12-24
inches) in front of the vehicle grille.
C. Engage the engine cooling fan (unless viscous fan drive).
D. Close the hood, being careful not to damage the equipment.
E. Insert a thermometer into the passenger side, left instrument
panel vent. Do not allow the thermometer to touch the sides of
the duct. Insert a second thermometer into the lower passenger
bunk vent.

Yes: System is operating
correctly. Discuss concern with
customer.
No: Gauge readings are out of
specification: Go to Air
Conditioning Mechanical
Pressures Diagnostics
IK1900225
No: Gauge readings are
correct but cab vent
temperature is out of
specification: Go to Air
Conditioning Control Head
Diagnostics IK1900226

F. Start the engine and raise the idle speed to 1500 rpm.
G. Open windows and close both cab doors.
H. Set the mode control to: NORM A/C; Highest blower speed;
Coldest cooling temperature.
I. Operate the system for five minutes, or until gauge readings
settle.
J. Record the following data:
Test Point

Value

Ambient Air Temperature
Relative Humidity
Cab Air duct Temp

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IK1900228 - 2010 and Newer Vehicle Air Conditioning Diagnostics (Start Here)

Page 6 of 7

Low-Side psi @ 1500 RPM
Compressor on (cut-in PSI)
Compressor off (cut-out PSI)
High-Side psi @ 1500 RPM
Compressor on (cut-in PSI)
Compressor off (cut-out PSI)
Lower Passenger bunk vent
temp
K. Compare gauge readings, vent temperature, ambient
temperature, and humidity to the appropriate HVAC System
Pressure Test Chart.
Does the Cab and rear HVAC operate correctly?

Step Action
Rear A/C Test:
A. Start engine and raise engine speed to 1500 RPM.
B. Turn cab A/C switch to NORM
C. Turn cab blower switch to highest speed.
D. Turn cab temperature switch to coldest position.

Decision
Yes: Rear HVAC system
operates correctly
No: Rear A/C does not
function: Go to Rear Air
Conditioning Electrical and
Mechanical Diagnostics
IK1900227

E. Shut both cab doors and open both windows.

7

F. Use the dash SLPR-FAN switch to vary rear blower speed from No: Rear control panel TEMP
and FAN switches are
lowest to highest speed.
inoperative while SLPR-TEMP
G. Use the dash SLPR-TEMP switch to vary sleeper temperature and SLPR­FAN switches
function: Go to Rear A/C
from warmest setting to the coldest setting.
Control Panel Inoperative
IK1900231
H. Use the Rear HVAC Control panel blower switch to raise and
lower rear blower speed.
I. Use the Rear HVAC Control panel TEMP switch to raise and
lower the duct air Temperature.
J. Review rear duct temperature recorded in step-6
Do the dash SLPR-FAN and SLPR-TEMP switches control the rear
A/C?

No: One or both SLPR TEMP
and SLPR FAN switches are
inoperative but rear control
panel TEMP and FAN switches
functions correctly: Go to
Sleeper Fan and Sleeper TEMP
Switch Inoperative IK1900232

Do the rear control panel blower speed and temperature switches
control the rear A/C?
Does the stabilized rear duct temperature from step-6 meet
specifications (See appropriate 2010 HVAC SYSTEM PRESSURE
TEST CHART)?

No: Front and rear controls
function correctly, but rear A/C
blows warm air: Go to Rear A/C
Blows Warm Air IK1900231

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IK1900228 - 2010 and Newer Vehicle Air Conditioning Diagnostics (Start Here)

Page 7 of 7

WARRANTY INFORMATION
Standard Repair Times: Due to the variety of vehicle confirgurations and number of components affected,
reference the SRT Manual (quick links below) for repair times.
Description
A/C SYSTEM PRELIMINARY DIAGNOSIS (EXCEPT 5000, 9000 SERIES), PERFORM
A/C MECHANICAL PRESSURES DIAGNOSIS (EXCEPT 5000, 9000 SERIES), PERFORM
A/C ELECTRICAL DIAGNOSIS ( EXCEPT 5000, 9000 SERIES) , PERFORM
A/C CONTROL HEAD DIAGNOSIS
A/C REAR UNIT ELECTRICAL AND MECHANICAL DIAGNOSIS (EXCEPT 5000,9000 SERIES),
PERFORM
SRT Manual

OTHER RESOURCES
Document
Number

Description

S16046

HEAT VENTILATION AIR CONDITIONING (HVAC) FOR 2010 ­ 3200 Bus, DuraStar®,
TerraStar™, TranStar®, WorkStar® Models

0000002221

HEAT VENTILATION AIR CONDITIONING (HVAC) FOR 2010 ProStar and LoneStar
Models (Formerly S16047)

IK1900207

2010 and Later ProStar and LoneStar HVAC Information

IK1900022

A/C Refrigerant and Oil Capacities

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