INSUFFICIENT COOLING IN HIGH AMBIENT TEMPERATURES

SUBJECT: INSUFFICIENT COOLING IN HIGH AMBIENT TEMPERATURES LVE/INSULATOR CO

VEHICLES AFFECTED: 1988-90 R/V TRUCKS W/A/C C60, C69

Some of the R/V model trucks from 1988 through 1990, either with or without rear A/C, may receive comments of insufficient cooling in high ambient temperatures. To address this condition a water shut off valve which operates during Max A/C and an insulator cover for the accumulator may be added. In addition, the refrigerant charge has been revised to increase air conditioning performance.

SERVICE PROCEDURES:

Water Valve Installation:

CAUTION:

Coolant may be pressurized and hot. Use care to ensure that the coolant is at ambient temperature. Possible burns could result from contact with hot coolant.

1. Drain the coolant.

2. Cut the front heater inlet and outlet hoses approximately 8" from the cowl. Refer to Figure 1. It may be necessary to cut about 1" out of each hose to allow the water heater valve (3) to be inserted. The exact amount of hose will depend on hose routing for different engine configurations and whether the vehicle has a rear heater water valve.

3. Insert the front heater water valve (3) in the hoses and install the hose clamp (1). Torque the clamps to 1.4-2.0 N.m (12-18 in.lbs.).

IMPORTANT: If the wiring for the blower relay evidences any interference with the valve, add convoluted conduit to protect the wires and tie strap the wires as necessary to avoid rubbing.

4. Install the plastic vacuum line on the water valve fitting and add a 3/32 rubber sleeve for coupling. Refer to Figure 1. Route vacuum line with the blower harness to the grommet into the dash area. Refer to Figure 2.

5. Punch a hole in the grommet with a pick, being careful not to puncture existing vacuum lines or wiring harnesses.

6. Route the vacuum line under the dash to the glove box area. Refer to Figure 3.

7. Open the glove box and fold the compartment down to gain access to the rear of the dash. Locate the Max A/C line going to the plenum valve and air recirculation door valve. The line is black plastic with an orange stripe.

8. Cut the line and insert Tee coupling. Refer to view "A" of Figure 3. Use 3/32 rubber vacuum line for the coupling. Install the added vacuum line to the bottom leg of the Tee.

Accumulator Insulation Installation:

1. Install the upper and lower insulators (2) and (3) on the A/C accumulator assembly. Refer to Figure 4.

2. Install the clamp (4) on the insulators at the overlapped portion and tighten the clamp.

Revised Refrigerant Charge:

1. Check the refrigerant (Freon 12) pressures per service manual. If discharge pressures are high, revise the A/C charge as follows:

A. Front air conditioning (C60): Reduce the charge from 3.25 lbs. to 3.0 lbs. B. Rear air conditioning (C69): Reduce the charge from 5.25 lbs. to 4.5 lbs.

2. Refer to section 1B of the service manual, page 1B-13, for charging and discharging procedures.

Inspection:

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1. Start the engine and check all hose connections for leaks.

2. Place the climate control lever in the "Max A/C" position and ensure that the water valve is operating properly.

PARTS INFORMATION:

Part Number Description Number ----------- ------------ ------ 14044414 Valve, heater water 1 15612120 Insulator, accumulator lower 1 15612121 Insulator, accumulator upper 1 15530486 Clamp insulator 1 549589 Clamp, water hose 8 6272766 Tee, vacuum hose 1 * Hose, 3/4" heater water as req'd * Hose, 5/8" heater water as req'd * Hose, vacuum, plastic as req'd * Hose, vacuum, 3/32" rubber as req'd * Refrigerant 12 (Freon) as req'd

Part may be obtained locally.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.