Pressure Transducer
Diagnostics in IK1900223)
and then go to step 24.

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

Does the HVAC _High_Side_Pressure value converted to PSI match
the gauge within +/- 10 psi?

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

Step Action

Page 6 of 11

Decision

Hose/Line Visual Inspection:

A. Perform visual inspection of hose/line between evaporator housing and
the Low-Side side of the compressor.

Yes: Repair as needed and then go to step
24.

10 NOTE:On sleeper vehicles this symptom would occur only if the hose/line
damage (restriction) occurs in the section of Low-Side line common to
both front and rear A/C systems.
Is the hose/line damaged?
No: Go to Step 11

Step Action

Decision

Low refrigerant charge:

A. Visually inspect all joints and seals in the air conditioning system. Look
for joints and seals that are dirty.

Yes: Repair leak and then go to step 24.

11 B. Clean area around dirty seal or joint and then starting with the dirty
joints and seals use leak detection tool to test for leaks.
Was a leak located?

Step Action

No: Go to step 12.

Decision

Yes: Go to step 13.
Verify Charge Quantity

A. Use a recovery station to recover the refrigerant from the system
No: Evacuate system until
and record the quantity of refrigerant recovered. Compare recovered
pressure measure 1000
12 quantity to charge specifications.
microns or less. If this value
cannot be reached, refer to
LEAK DETECTION. Go to
Was the charge quantity low?
step-24.

Step Action

13

Decision

Yes: After flushing is complete go to step 24.
Expansion Valve Debris/Moisture:

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

A. Remove expansion valve. Check for debris in inlet port.
NOTE:On sleeper vehicles this symptom would only occur if BOTH
expansion valves are blocked by debris or freeze up from moisture.

Page 7 of 11

No: Evacuate system until
pressure measure 1000
microns or less. After proper
evacuation is reached, go to
step 24.

Is there debris in the system?

Step Action

Decision

Yes: Go to step 15.

Expansion Valve Check

A. Start engine and turn A/C to NORM, highest fan speed, and coldest
14 temperature.
B. After 5 minutes of operation, feel the expansion valve.

No: Replace compressor.
Check for debris and then
flush system if necessary.
Replace expansion valve and
then go to step 24.

Is the expansion valve extremely cold?

Step Action

Decision

Yes: Go to step 16.

Expansion Valve Debris

A. Remove the expansion valve and check for debris at the inlet port.
15

Are there traces of aluminum or desiccant particles?

Step Action
Debris in system

16

No: Obtain replacement
compressor, but do not install
until completing step 16.

Decision
After inspection and any required repairs, go
to step 24.

A. Click the following link to check for system damage: A/C system flush
tool

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

Step Action

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Decision

Added Air Flow
Yes: Readings are normal. Return to
IK1900228 and continue Performance test

A. Operate a large fan in front of the condenser and recheck readings.
17

with fan.

NOTE: These readings may indicate normal operation for a stationary
vehicle.
Are readings normal with the fan blowing in front of the condenser?

Step Action

No: Remove the large fan and
then go to step-18.

Decision

Yes: Go to step 19.

A. Review static pressure recorded in IK1900228.
18 Note: If static pressure were not measured, see Static Pressure in
IK1900228 for test conditions.
Was static pressure correct?
Static pressure

Step Action

No: If static pressure is not
correct, go to step 1 of this
procedure.

Decision

Yes: Go to step 20.
Cooling Module Inspection

19
Is air flow restricted?
A. Inspect Radiator, CAC, and A/C Condenser, for debris between the
components and clogged fins.

Step Action

No: Go to step 21.

Decision
Yes: Go to step 24.

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

B. Start engine and turn A/C to NORM, highest fan speed, and coldest
temperature. After 5 minutes of operation use temperature probe to
measure vent temperature.

Page 9 of 11

No: Check engine fan, fan
shroud, and fan clutch
operation. Repair as needed
and then go to step 24.

CAUTION:To prevent radiator damage, do not hold direct high pressure
20 water or air close to the radiator fins.
Is system performance correct?
Radiator Exterior Back-Flush

A. Use a pressure washer on the fan side of the system to back flush the
debris out the front of the cooling module.

Step Action

Decision

Cab Air Leak

Yes: Repair cab fresh-air leaks as required,

A. Check for exterior air leaks into the cab.

and then go to step 24.

21
Are there exterior air leak?
No: Go to step 22.

Step Action

Decision

Heater Shut Off Valves

22

A. Verify heater shut off valve is closed (If equipped).

Is heater valve closed?

Step Action

23

Blend Door Calibration

Recalibrate the front interior actuator / door position by performing the
following steps:

Yes: Go to step 23.

Yes: Close valve and retest.

Decision

Yes: Go to step 23.
No: Go to step 10 of HVAC Control Head
Issues (IK1900226)

A. Turn the ignition switch to the ON position.
B. Set Blower Fan Speed Control to any speed (1 - 7).
C. Set Mode Control to Defrost.

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

Page 10 of 11

D. Remove fuse panel cover, and remove the HVAC 5 Amp fuse (fuse
position F1­B) for battery to HVAC Control head.
NOTE: Do not operate the HVAC control panel controls during the
recalibration.
E. Wait approximately 30 seconds, and reinstall the fuse.
F. Listen for the sound of actuators moving the Mode, Blend, and Fresh /
Recirculate doors through their full range of motion.
G. Start the vehicle, and check for correct operation of all HVAC modes
and temperature.

Did recalibration fix the issue?

Step Action

Decision

Assemble and Test:

After problem is detected and repaired, perform A/C recovery, system
24 flush if required, oil calculations, pressure test, evacuation, and recharge
to return system to working condition. Verify system works correctly and
operator concern is corrected

Return vehicle to customer.

WARRANTY INFORMATION
NOTE: There are multiple noun groups that the diagnostic time could be charged to.

WARRANTY CLAIM CODING:
Group: 19000 -Truck Air Conditioner
Noun: Multiple Nouns - Code to repair made

Warranty Coding Manual

STANDARD REPAIR TIMES:
19 - AIR CONDITIONING SYSTEM INSPECTION/PERFORMANCE DIAGNOSTICS

Hours

Code

Varies
by
model

A/C MECHANICAL PRESSURES DIAGNOSIS
(EXCEPT 5000, 9000 SERIES), PERFORM

Model

Engine

All

All

Link to the Standard Repair Time Manual: Click Here

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

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