Pressure Transducer Check:
A. Start engine
B. Turn the A/C Control to Max, Fan On, and Temp control to
coldest setting.

Yes: There is moisture or too much oil in
system. Repair as need and the go to step 24.

C. Use DLB to monitor A/C_High_Side_Pressure signal.
D. Use the A/C charging station gauges to monitor high-side pressure.
9
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.
No: Repair as needed (See Pressure Transducer
Diagnostics in IK1900223)
and then go to step 24.
Does the HVAC _High_Side_Pressure value converted to PSI match
the gauge within +/- 10 psi?

Step Action

Hose/Line Visual Inspection:

Decision

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

A. Perform visual inspection of hose/line between evaporator housing and the Low-Side side of the compressor.
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?
No: Go to step 12.

Step Action

Decision

Yes: Go to step 13.
Verify Charge Quantity
12

A. Use a recovery station to recover the refrigerant from the system and record the quantity of refrigerant recovered. Compare
recovered quantity to charge specifications.

Was the charge quantity low?

No: Evacuate system until pressure measure 1000
microns or less. If this value cannot be reached, refer
to LEAK DETECTION. Go to step­24.

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

Step Action

Expansion Valve Debris/Moisture:

13

Page 6 of 9

Decision

Yes: After flushing is complete go to step 24.

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.
Is there debris in the system?

Step Action

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

Decision

Yes: Go to step 15.

Expansion Valve Check
14

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

Is the expansion valve extremely cold?

Step Action

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

Decision

Yes: Go to step 16.

Expansion Valve Debris
15

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

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

Added Air Flow
A. Operate a large fan in front of the condenser and recheck readings.

Page 7 of 9

Decision

Yes: Readings are normal. Return to
IK1900228 and continue Performance test
with fan.

17
NOTE: These readings may indicate normal operation for a stationary vehicle.
Are readings normal with the fan blowing in front of the condenser?
No: Remove the large fan and then go to step-18.

Step Action

Decision

Yes: Go to step 19.
Static pressure
18

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

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

Step Action

Decision

Yes: Go to step 20.
Cooling Module Inspection
19

A. Inspect Radiator, CAC, and A/C Condenser, for debris between the components and clogged fins.

Is air flow restricted?
No: Go to step 21.

Step Action

Decision

Yes: Go to step 24.
Radiator Exterior Back-Flush

20

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

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 water or air close to the radiator fins.
Is system performance correct?

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

Step Action

Cab Air Leak
A. Check for exterior air leaks into the cab.

Page 8 of 9

Decision

Yes: Repair cab fresh-air leaks as required,
and then go to step 24.

21
Are there exterior air leak?

No: Go to step 22.

Step Action

Decision

Heater Shut Off Valves
Yes: Go to step 23.
22

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

Is heater valve closed?

Yes: Close valve and retest.

Step Action

Decision

Blend Door Calibration
Recalibrate the front interior actuator / door position by performing the following steps:
A. Turn the ignition switch to the ON position.

Yes: Go to step 23.

B. Set Blower Fan Speed Control to any speed (1 - 7).
C. Set Mode Control to Defrost.
23

D. Remove fuse panel cover, and remove the HVAC 5 Amp fuse (fuse position F1-B) 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.

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

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:
24

After problem is detected and repaired, perform A/C recovery, system 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.

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IK1900225 ­ Air Conditioning Mechanical Pressures Diagnostics

Page 9 of 9

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

Model

Engine

Varies
by
model

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

All

All

Link to the Standard Repair Time Manual: Click Here

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