HVAC System: Other Ford Windstar I

Function Control

The heater and power ventilation control includes

1. A function selector switch knob for PANEL, PANEL/FLOOR, OFF, FLOOR, DEFROST/FLOOR and DEFROST that determines the manner in which the system will operate.
2. Each position of the function selector switch knob and heater blower motor switch is detented for positive engagement.
3. The function selector switch is a vacuum selector valve combined with an internal electrical switch.

Temperature Control

The temperature control knob is for manually setting the desired comfort temperature. (Scheme 38)

The temperature control knob connects through an electronic blend door actuator motor to the air temperature control door of the evaporator housing. (Scheme 39)

The vacuum selector valve directs source vacuum to various vacuum control motors.

1. Two internal single-pole electrical switches are controlled by the selector.
2. One internal electrical switch controls the electrical supply to the heater blower motor switch.

The four-speed heater blower motor switch controls blower motor speed and is manually set to select the desired airflow.

The temperature control knob is connected to the air temperature control door by an electronic door actuator motor. Movement of the control knob from COOL to WARM causes a corresponding movement on the air temperature control door and determines the temperature that the system will maintain. (Scheme 40)

The system uses a temperature blend method to provide controlled temperature to the vehicle interior. All outside airflow from the blower passes through the A/C evaporator housing.

Temperature is regulated by heating a portion of the outside air and blending it with the remaining cooler outside air to the desired temperature. Blending is varied by the air temperature control door which controls the amount of air that flows through or around the heater core, where it is mixed and directed into the distribution plenum.

Depending upon the selection made with the function selector switch knob, the air is directed to

1. Heater Ducts.
2. Windshield Defroster Nozzle.
3. Instrument Panel Registers.

System airflow is manually controlled by the control assembly. A vacuum selector valve, controlled by the function selector switch knob, distributes vacuum to the various door vacuum control motors. These vacuum control motors direct the airflow through the system.

Scheme 38

Scheme 39

Scheme 40

Heater Blower Motor Control

The heater blower motor switch is an electrical switch that provides four manually selected speeds of heater blower motor operation.

HEATER BLOWER MOTOR RESISTOR

The heater blower motor resistor is located on the bottom passenger side of the A/C evaporator housing behind the glove compartment.

Three resistance elements are mounted on the resistor board to provide four heater blower motor speeds.

Depending on the blower switch position, series resistance is added or bypassed in the heater blower motor circuit to decrease or increase heater blower motor speed.

The heater blower motor resistor assembly, which is similar to a standard resistor assembly, operates as follows

1. An overheating protective device (thermal limiter) has been added to prevent heat damage to the A/C evaporator housing.
2. Overheating of the resistor coil(s) will occur when system produces excessive heat, replace only with identical replacement.
3. Do not substitute heater blower motor resistor with a standard assembly which does not include a thermal limiter device.

HEATER BLOWER MOTOR THERMAL LIMITER

The thermal limiter, used in the heater blower motor resistor, performs the following functions

1. Serves As A Fuse Which Protects The System From Overheating.
2. Is Located A Predetermined Distance From Resistor Coils And In Series With The Coil Circuit.
3. Will Open The Resistor Coil Circuit When Temperature Of The Thermal Limiter Reaches 121°C (250°F).

Spring contacts separate when the wax softens, opening the heater blower motor switch resistor circuit. Replace entire heater blower motor resistor assembly because spring contacts cannot be closed again.

HEATER CORE

The heater core consists of a number of fins and tubes in an arrangement to extract available heat from the engine coolant and transfer that heat to the air that passes through the heater core. (Scheme 41)

Scheme 41

SYSTEM AIRFLOW

The heater assembly is a blend air system, receiving outside air through the blower inlet, which is connected directly to an opening in the upper cowl.

Outside air is drawn into the system from the cowl, through the blower inlet into the A/C evaporator housing.

It is directed through and/or around the heater core, mixed and discharged through outlets in the heater outlet floor duct to the floor area, or through the windshield defroster nozzle, as desired.

The illustrations show how air is circulated through the system when the mode is in each of its detent positions. (Scheme 42)- (Scheme 46).

The illustrations show how the five lines in the A/C plenum vacuum harness are controlled by a selector valve assembly to operate three vacuum control motors.

The vacuum control motors control the movement of

1. The Heater Air Inlet Duct Door.
2. The Panel/Floor Door.
3. The Windshield Defroster Door.

Scheme 42

Scheme 43

Scheme 44

Scheme 45

Scheme 46

Off

When the function selector switch knob is in the OFF position

Scheme 47

1. The A/C damper inlet door is at full vacuum. As a result, outside air is closed off from the system. (Scheme 47)
2. The air temperature control door may be positioned anywhere within the range of FULL HEAT to FULL COOL.
3. The blower motor is off.

Panel

When the function selector switch knob is in the PANEL position

1. The heater air inlet duct door, with no vacuum being applied, will block recirculated air and admit outside air. From there, air flows through the system to the instrument panel registers. (Scheme 48)
2. The heater air damper door is at full vacuum, airflow is directed to the instrument panel registers.
3. The windshield defroster door is at full vacuum, closing off airflow to the windshield defroster nozzle.
4. The airflow is admitted into the system when the function selector switch knob is in the PANEL position. The air temperature control door may be positioned anywhere from full heat to full cool to mix air flowing through the heater core and air from outside to achieve the desired temperature level.

Scheme 48

Floor

When the function selector switch knob is in the FLOOR position

1. Most of the system's air supply is directed to the floor outlets with a small amount going to the windshield and side window demisters. (Scheme 49)

Scheme 49

1. The heater air inlet duct door is in the no vacuum position, blocking recirculating air and admitting outside air.
2. The windshield defroster door is in the vacuum position, closing off all but a minimum of airflow to the windshield defroster nozzle.
3. The air temperature control door may be positioned anywhere from full heat to full cool to mix air flowing through the heater core and air from outside to achieve the desired temperature level.
4. The heater air damper door is in the no vacuum position, blocking air circulation to the instrument panel registers.

Defrost

When the function selector switch knob is in the DEFROST position

1. The heater air inlet duct door is in the no vacuum position, admitting outside air. (Scheme 50)
2. The heater air damper door is in the no vacuum position blocking airflow to the instrument panel registers.
3. The windshield defroster door is in the no vacuum position, so that most of the incoming air is directed to the windshield defroster nozzle. There is slight airflow to the floor and side windows.
4. The air temperature control door may be positioned anywhere from full heat to full cool to mix air flowing through the heater core and air from outside to achieve the desired temperature level.

Scheme 50

MINI-TUBE VACUUM HOSES

Mini-tube vacuum hoses are used in the A/C plenum vacuum harness assemblies.

They provide greater flexibility with less tendency to collapse and are less susceptible to pinching.

HEATER SYSTEM VACUUM

The panel/floor door and the windshield defroster door vacuum control motor have two vacuum lines to each motor. (Scheme 51)

1. When vacuum is applied to both lines, the doors move to their full vacuum positions.
2. When vacuum is applied to the end port line only, the doors move to their partial vacuum positions.
3. If vacuum is applied to the side port line only (or neither line), the doors assume their no-vacuum positions. See «VACUUM DIAGRAMS»(ref-138026-S40541344042002032000000) .

Scheme 51

MINI-TUBE VACUUM HOSE

Mini-tube vacuum hoses are provided in the A/C plenum vacuum harness. They provide greater flexibility with less tendency to collapse and are less susceptible to pinching. Service of damaged hoses is easily made using a short piece of standard 3 mm (1.8 inch) inside diameter (ID) vacuum hose and inserting the cut ends of the mini-tube into the ends of the standard 3 mm (1.8 inch) inside diameter (ID) vacuum hose. The following illustrates an in-line and tee connector installation.

1. Measure length of damaged area of the mini-tube vacuum hose.
2. Cut a piece of standard 3 mm (1/8 inch) inside diameter (ID) vacuum hose approximately 25 mm (1 inch) longer than damaged area of the mini-tube vacuum hose.
3. Cut off the mini-tube vacuum hose on each side of damaged area.
4. Dip the mini-tube hose ends in commercially available paint thinner containing methyl ethyl ketone. This solvent will seal the mini-tube in the vacuum hose. (Scheme 52)
5. Insert ends of the mini-tube vacuum hose approximately 9 mm (3/8 inch) into ends of standard 3 mm (1/8 inch) service vacuum hose section.
6. Shake service joint after assembly to make sure solvent is dispersed and vacuum line is not plugged.
7. Test system for a vacuum leak in service area using Rotunda Vacuum Tester (014-R1054) or equivalent.

Scheme 52

SYSTEM TESTS

SYMPTOM INDEX

Note. If the thermal limiter has no continuity, it is necessary to replace the whole heater blower motor resistor. See HEATER BLOWER MOTOR RESISTOR ASSEMBLY under REMOVAL & INSTALLATION.

BLOWER MOTOR SWITCH

Note. To test blower motor switch, see BLOWER SWITCH CONTINUITY. (Scheme 53)

BLOWER SWITCH CONTINUITY

Scheme 53

HEATER WATER HOSES

Note. When servicing heater core and engine cooling system components, do not reuse constant tension hose clamps. Discard them and replace with suitable worm-gear type hose clamps.