A/C - Poor Heater Output

U00992

LACK OF HEATER OUTPUT

APPLICABLE MODELS
1990-91 Protege (BP DOHC Engine)

DESCRIPTION





Some 1990-'91 Proteges with the BP DOHC engine may experience insufficient heater output. This may be the result of a machining process where a piece of casting flash from the blind plug hole on the cylinder head is not completely removed. Figure 1.

Cooling system pressure forces the piece of casting flash into the thermostat housing area where it blocks the heater hose inlet passage.

The result is restricted coolant flow to the heater core causing insufficient heat output.

The machining process has been changed since August 1, 1991.

If the problem exists on a vehicle with a cylinder head produced prior to August 1, 1991, check the heater pipe inlet for a piece of casting flash material.

Follow the Inspection and Repair Procedures shown in this bulletin.





VIN OF PRODUCTION CHANGE

* The revised section indicated by an asterisk. Please replace the original bulletin with this revised bulletin. (See Labor Time)

INSPECTION & REPAIR PROCEDURES





1. Check the punch mark numbers on the cylinder head to determine production date. If the numbers read 8-1-1 or later, the cylinder head was manufactured using a modified machining process and does not require further inspection. Figure 2.

2. If the punch mark indicates a production date prior to August 1, 1991, remove the thermostat according to procedures in the Workshop Manual.





3. Inspect the thermostat housing area with your fingers, paying particular attention to the immediate area of the heater pipe inlet. Figure 3.

Be careful of sharp edges while searching for the casting flash.

4. If you find a piece of the casting flash approximately the size of a dime - remove it from the thermostat housing. Curved needle-nose pliers may be necessary to remove a wedged casting flash.

NOTE:
Carefully blowing compressed air into thermostat housing area may help move the casting flash into a better position for removal.

5. Install the thermostat and replenish the coolant.

NOTE:
To prevent damage to the water outlet, tighten the two bolts evenly until the proper torque specification is reached (19-26 Nm) 1.9-2.6 m-kg 14-19 ft lb.

6. Recheck the heater output to the passenger compartment.





WARRANTY INFORMATION

(Applies to vehicles covered under warranty).





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