Mechanically Controlled Thermostatic With Vacuum Override

Procedure
1. Disconnect duct and valve assembly from air cleaner, hoses and other components and remove.
2. Make sure that duct door moves freely. Repair or replace as necessary.
3. With ambient temperature less than 73° F, check operation of duct door using an external vacuum source as follows:
a. With no vacuum applied to vacuum motor, the duct door must be within .60 inch or less of being in the heat off position. If the door is not in this position after 10 minutes, replace duct and valve assembly.
b. Apply 1-5 inches Hg vacuum to vacuum motor. The duct door should start to move toward the heat-on position. Repair or replace as necessary.
c. Apply 7-12 inches Hg vacuum to vacuum motor. The duct door should be in the heat on position within one minute. If not, replace or repair as required.

NOTE: Do not allow vacuum to drop below 7 inches Hg or rise above 12 inches Hg vacuum while performing the following steps.

4. Immerse duct and valve assembly in water so that bulb end of thermostat is submerged in water.
5. With water temperature at 50-60° F, the duct door should be in the heat on position within 10 minutes. If not, replace duct and valve assembly.
6. With water temperature at 120-130° F, the duct door should move toward the heat off position within 10 minutes. If not, repair or replace as necessary.
7. Remove assembly from water and disconnect vacuum source hose.
8. Thoroughly dry assembly before installation. Check all components for proper installation and/or damage. Repair or replace as required.