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Info - Service Diagnosis/Recommendations for Inoperative A/C Systems

Subject:Service Diagnosis/Recommendations for Inoperative A/C Systems

Models:1990-2002 Chevrolet and GMC H6-7 C-Series Conventional Medium Duty Models
1997-2002 Chevrolet and GMC F6-7 T-Series Tilt Cab Medium Duty Models
1997-2002 Isuzu FSR/FTR/FVR Medium Duty Commercial Models
with Sanden SD-7H15 A/C Compressor


A recent investigation of repair occurrences on some C-Series Conventional Medium Duty vehicles has revealed a number of A/C compressor clutch overheat conditions. These overheat conditions would adversely affect the clutch bearing and compressor shaft seal resulting in the loss of refrigerant charge and an inoperative A/C system.

This sequence of events has been frequently diagnosed as a primary compressor or clutch failure when in fact that may not be the case. The actual cause of the compressor failure was excessive clutch cycling because of low refrigerant charge or leaks in the system. The compressor clutch can cycle as much as 25-30 times a minute under a low charge condition. This is especially critical on a gas engine with much faster operating RPMs.

In an effort to promote complete customer satisfaction, use the following service diagnosis/recommendation information. Properly diagnose and correct all refrigerant leaks. Replace the A/C compressor or clutch as required. Using the following strategy-based diagnostic information/procedures should ensure a successful first-time repair.

A/C System Diagnosis

When a vehicle exhibits an A/C condition, a thorough system diagnosis, including a compressor test, should be completed. Refer to the HVAC section of the applicable Medium Duty Service Manual for complete diagnostic information and procedures.

The purpose of the following tests is to identify functioning compressors before the compressor is removed from the vehicle. Functioning compressors should produce both high and low pressure. If a compressor fails any one of the following tests (voltage test, resistance test, rotation test or low/high pressure tests), the compressor can be considered inoperative and can then be removed from the vehicle.

Charge Level Confirmation

Test

Specification / Value

Result/Answer

What is the system charge level?

*Refer to Refrigerant System Capacity table below.

______ lb of R134a

*The A/C system must be correctly charged to specification. Incorrect diagnosis may occur if the system is not correctly charged. This is best accomplished by evacuating and re-charging to the correct level. Replace the oil from the recovery machine back into the system.

Voltage Test

Test

Specification / Value

Result/Answer

What is the voltage of the clutch at idle?

*11.5 volts minimum

______ volts

*With the A/C on, the compressor clutch should be receiving a minimum of 11.5 volts.

Resistance Test

Test

Specification / Value

Result/Answer

What is the resistance measured through the clutch coil?

*2.8-4.4 ohms

______ ohms

*The correct resistance through the clutch coil is 2.8 to 4.4 ohms.

Rotation Test

Test

Specification / Value

Result/Answer

Is the compressor rotation smooth?

 

______ Y or N

The clockwise rotation of the compressor shaft should be smooth without binding.

Low Pressure Test (Suction Side)

Test

Specification / Value

Result/Answer

Can the compressor pull lower than 103 kPa (15 psi)?

 

______ Y or N

  1. Bypass the low-pressure switch. Unplug the harness. Install a jumper wire.
  2. Start the A/C.

High Pressure Test

Test

Specification / Value

Result/Answer

Can the compressor build head pressure exceeding 2413 kPa (350 psi) following the steps below ?

 

______ Y or N

  1. Reconnect the low-pressure switch.
  2. Start the A/C.
  3. Place a sheet of cardboard over the condenser to block airflow. Limiting the airflow over the condenser will cause head pressure to increase.
  4. Remove the cardboard immediately after the compressor exceeds 2413 kPa (350 psi).

Refrigerant Leak Testing

Tools Required

    • J 41995 or J 46053 or J 46054 A/C Leak Detector
    • J 41447 R134a A/C Tracer Dye (box of 24)
    • J 42220 Universal 12V Leak Detection Lamp
    • J 43872 Fluorescent Dye Cleaner

A primary cause of an inoperative A/C compressor or clutch is low refrigerant charge. A low charge may cause excessive clutch cycling and clutch overheat. For this reason, ALL VEHICLES BEING REPAIRED FOR AN A/C CONCERN MUST BE THOROUGHLY LEAK TESTED WITH ANY OF THE ABOVE LEAK DETECTORS OR J 41447 TRACER DYE BEFORE BEING RETURNED TO SERVICE.

All future 2003 Medium Duty vehicles will have tracer dye installed during production.

Refrigerant System Capacities

Important: 

   • Service replacement Sanden compressors come already filled with 240 ml (8 oz) of PAG oil. This is enough for a COMPLETE system fill. The total system capacity is 240 ml (8 oz). For this reason, this oil must be drained out. Refill the system with only as much PAG oil as was removed from the replaced component.
   • The refrigerant charge MUST be correct. Verify the correct refrigerant charge.

When recharging an A/C system, you MUST use the proper amount of refrigerant and PAG oil. Refer to the Refrigerant System Capacities tables below.

Refrigerant System Capacities (C Models)

Application

Specification

Metric

English

PAG Oil (P/N  12345923 -- U.S.)

PAG Oil (P/N  10953486 -- Canada)

  • Accumulator Replacement

*

*

* Add 60 ml (2 oz) of PAG oil plus the equal amount of oil drained from the old accumulator.

  • Compressor Replacement

60 ml*

2 oz*

  • Condenser Replacement

30 ml*

1 oz*

  • Evaporator Replacement

90 ml*

3 oz*

  • Receiver/Dehydrator Replacement

30 ml*

1 oz*

  • Total System PAG Oil Capacity

240 ml

8 oz

R-134a

  • Refrigerant Charge

1.13 kg

2.5 lb

* If more than the specified amount of PAG oil was drained from a component, add the equal amount drained.

Refrigerant System Capacities (F Models)

Application

Specification

Metric

English

PAG Oil (P/N  12345923 -- U.S.)

PAG Oil (P/N  10953486 -- Canada)

  • Compressor Replacement

60 ml*

2 oz*

  • Condenser Replacement

30 ml*

1 oz*

  • Evaporator Replacement

50.2 ml*

1.7 oz*

  • Receiver/Dehydrator Replacement

8.9 ml*

0.3 oz*

  • Total System PAG Oil Capacity

240 ml

8 oz

R-134a

  • Refrigerant Charge

0.91 kg

2.0 lb

* If more than the specified amount of PAG oil was drained from a component, add the equal amount drained.

When a compressor or other component is removed from the vehicle, drain and measure the PAG oil before replacement.

Additional Information

Additional Sanden technical information can be obtained on the following website. Included on this website are Sanden Technical Bulletins, a complete compressor service manual and download library.

http://www.sanden.com/support/index.html