Cold Engine Test

COLD OPERATION
Bleed Valve Closed, manifold vacuum builds)
Diaphragm Vacuum pulls up on the air door
Air Control Door Rises, pre-heated air enters air cleaner. (Cold air blocked).
Check Valve Prevents vacuum loss at full throttle.
Fixed Orifice Prevents rapid pressure changes. Allows smooth operation of control door.

Fig. 40 Air Control Door:

COLD ENGINE TEST

1. Disconnect the air intake duct and start the engine. The air door should rise (opening the heated air passage and closing the fresh air passage), Fig. 40.

Fig. 41 Testing For Vacuum To The Air Control Door:

2. If the air door does not rise, disconnect the vacuum hose from the air control diaphragm and check for vacuum, Fig. 41. Vacuum should be available.
a. If vacuum is available, check the movement of the air door. If it moves freely, replace the air control diaphragm and re-test.
b. If no vacuum is available, check the #8 vacuum hose for proper connection, cracking or blockages, and repair as necessary. If the hose is OK, replace the air bleed valve A.