Thermostatic Air Cleaner Vacuum Switch: Testing and Inspection

Procedure

1. Cool modulator to below 40° F (except black modulator) or 20° F (black modulator). Allow enough time for modulator temperature to stabilize and modulator valve to close.

2. On 1975-76 systems, use an external vacuum source and apply at least 16 inches Hg vacuum to vacuum motor side and trap vacuum by pinching hose. Modulator must hold at least 14 inches Hg vacuum for 60 seconds. If not, replace modulator.

3. On 1977-80 systems, use a 24 inch length of 1/4 inch hose between cold weather modulator and vacuum gauge. Using an external vacuum source, apply at least 16 inches Hg vacuum to vacuum motor side of modulator and trap vacuum by pinching hose. The modulator must hold at least 5 inches Hg vacuum for 30 seconds. If not, replace modulator.