DESCRIPTION
Fresh air or heated air is made available to engine by ducting which directs air into air cleaner assembly. Air temperature is controlled by temperature-sensitive vacuum system that operates duct valve.
Vacuum-operated duct may select cool air from outside through pick-up tube, or warm air from exhaust manifold shroud. System consists of shroud, air cleaner assembly with vacuum motor, duct and valve assembly, temperature sensor and cold-weather modulator (if equipped). (Scheme 37)
OPERATION
When engine is cold, air is selected from exhaust manifold shroud. During the "open" position, vacuum is applied to vacuum motor operating the duct valve. (Scheme 36) Duct valve closes off fresh air supply. This allows heated air to enter air cleaner.
As engine becomes warm, temperature sensor operates, preventing vacuum from being applied to vacuum motor. In this "closed" position, duct valve closes off supply of heated air, allowing external air to flow through pick-up tube into air cleaner. (Scheme 36)
Cold-weather modulator controls inlet air temperature. Cold-weather modulator retains vacuum to maintain duct valve position. This is done during vacuum decrease due to acceleration. Cold-weather modulator will only operate at certain temperatures.
Scheme 36
AIR CLEANER TEMPERATURE SENSOR
- Temperature sensor should allow vacuum to close duct door at ambient temperatures below 75°F (24°C). Sensor should bleed off vacuum at certain temperature. This allows duct door to open to fresh air at specific temperature.
- Color code determines the temperature at which the vacuum bleeds off. Replace sensor if operating temperature is not within specification. See TEMPERATURE SENSOR SPECIFICATIONS.
| Application | Bleed Off Temperature |
|---|---|
| Brown | 75°F (24°C) |
| Pink | 90°F (32°C) |
| Black | 90°F (32°C) |
| Clear | 90°F (32°C) |
| Blue | 105°F (41°C) |
| Yellow | 105°F (41°C) |
| Green | 105°F (41°C) |
TEMPERATURE SENSOR SPECIFICATIONS
AIR CLEANER COLD WEATHER MODULATOR
- Using vacuum pump, apply 16 in. Hg of vacuum to the motor side of modulator. Note the ambient temperature and if vacuum reading is maintained or decreased.
- The vacuum should be maintained or decreased depending on ambient temperature. Replace assembly if vacuum reading is not within temperature specifications. See MODULATOR SWITCHING TEMPERATURE.
| Valve Color | Holds Vacuum | Leaks Vacuum |
|---|---|---|
| Black | Below 20°F (-7°C) | Above 35°F (2°C) |
| Blue | Below 40°F (4°C) | Above 55°F (13°C) |
| Green | Below 50°F (10°C) | Above 76°F (24°C) |
| Yellow | Above 65°F (18°C) | Below 50°F (10°C) |
MODULATOR SWITCHING TEMPERATURE
VACUUM MOTOR
Disconnect vacuum hose from vacuum motor connector tube. Apply a minimum of 8 in. Hg vacuum. Note vacuum motor stem operation. Stem should remain retracted as long as vacuum is applied. Replace assembly if stem will not remain retracted.
