Cold Weather Modulator (Ford Motor Co. Only)

On normally open modulators (blue, green or black), cool modulator to 40°F by spraying the vacuum control temperature sensor with R-12 refrigerant. On normally closed modulators (yellow), warm vacuum control temperature sensor to above 70° F.
CAUTION: Do not spray R-12 around a running engine or any other heat source. Heated R-12 vapors will create poisonous phosgene gas. Always perform this step in a well ventilated area.
Connect an external vacuum source between modulator and the vacuum gauge, using a 24" length of 1/4" I.D. vacuum hose.
Apply a minimum of 16 in. Hg to vacuum motor side of modulator. Modulator must not leak down to less than 5 in. Hg in 30 seconds. If it does, replace the modulator.

On normally open modulators, warm modulator to at least 70° F (for blue modulator), 80°F (green modulator) or 45° F (black modulator). On normally closed modulators (yellow), cool temperature sensor with R-12 refrigerant to below 40° F. If vacuum holds at these temperatures, modulator is not functioning and must be replaced.

Air Control Door Opening Vacuum

Application

⁽¹⁾Door Fully Closed Less Than In. Hg

⁽²⁾Door Fully Open Max. In. Hg

American Motors

151" 4-Cyl.

.....

258" 6-Cyl.

.....

Buick⁽⁴⁾

Cadillac

4-6

⁽³⁾

Chevrolet⁽⁴⁾

.....

Chrysler Corp.

1.7L 4-Cyl.

All Others

5.5

8.5

Ford Motor Co.

.....

Oldsmobile

151" 4-Cyl.⁽⁴⁾

.....

5-7

All Others

.....

5-7

Pontiac⁽⁴⁾

.....

⁽¹⁾	(1) - Closed to outside air (heated air position).

⁽²⁾	(2) - Closed to heated air (outside air position).

⁽³⁾	(3) - Manifold vacuum.

⁽⁴⁾	(4) - Some General Motors 151" 4-Cyl. engines do not use a vacuum motor.