Why does the heater only operate in the #5 position

DEFEAT THE HEATER, AND WHEN THE SERVICE MANUAL ARRIVES FIX IT
just unplug the heater. element end lead.

Hot water (coolant ) flows through the heater core all the time , no valve too let coolant into heater core . The amount of heat delivered to the passenger compartment is controlled by opening or closing the air temperature door. The coolant exits the heater core through the heater outlet hose and recirculates back through the engine cooling system.

Temp. blend door actuator is probably the issue . Do you hear any noise behind the instrument panel ?

Tick/click, chirp or groaning

Air Temperature Actuator
The air temperature actuator are 5-wire bi-directional electric motors that incorporate a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module removes power from both control circuits.

It's the switch.

Your thermostat could be stuck in an open position. This will result in your vehicle being underheated. Typically, a thermostat opens only when an engine reaches a certain operating temperature. If a thermostat is stuck in the open position, radiator coolant flows into an engine before it reaches normal operating temperature. This prevents adequate engine warming and results in engine underheating. DIY repair costs: $5-$10


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If your heater is not heating your vehicle adequately, it could be the result of a few different things:

1) Your thermostat could be stuck in an open position. This will result in your vehicle being underheated. Typically, a thermostat opens only when an engine reaches a certain operating temperature. If a thermostat is stuck in the open position, radiator coolant flows into an engine before it reaches normal operating temperature. This prevents adequate engine warming and results in engine underheating. DIY repair costs: $5-$10

2) Your radiator could be low on coolant. If this is found to be the cause, then you will have to inspect your coolant system for leaks. Depending upon what type of leak your vehicle has (if this is found to be the case), I would have this repair done by a shop unless it is something reasonable simple to fix like a water pump. Good Luck!

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I would follow the 5/8 inch heater hose to the firewall and look at the heat control valve position when the selector on the dash is toward cold. Then I would move the selector switch to hot and look at the valve position again. If it has not changed the cable is not operatiing the switch and needs replacing (providing the sdash selector is operating.

in the cab, but procedures are different depending on whether or not you have A/C. See below

1980-81 Comfort Vent Heaters, Without Air Conditioning

1. Disconnect the heater hoses from the heater core tubes and plug the hoses with suitable 5 / 8 inch; (16mm) plugs.
2. Remove the glove compartment liner.
3. Remove two (2) spring clips attaching the heater core cover to the plenum along the top edge of the heater core cover.
4. Remove eight (8) screws attaching the heater core cover to the plenum and remove the cover.
5. Remove the heater core from the plenum taking care not to spill coolant from the core.

To install:

1. Install the heater core in the plenum.
2. Install the heater core cover (eight (8) screws and two (2) spring clips along the top edge of the cover).
3. Install the glove compartment liner.
4. Connect the heater hoses to the heater core. Tighten the hose clamps.
5. Add coolant to raise the coolant level to specification.
6. Check the system for proper operation and for coolant leaks.

1980-81 Standard & High Output Heaters, Without Air Conditioning

1. Disconnect the temperature cable from the temperature blend door and the mounting bracket on top of the heater case.
2. Disconnect the wires from the blower motor resistor and the blower motor.
3. Disconnect the heater hoses from the heater core and plug the hoses with suitable 5 / 8 inch; (16mm) plugs.
4. Working under the instrument panel, remove two (2) nuts retaining the left end of the heater case and the right end of the plenum to the dash panel.
5. In the engine compartment, remove one (1) screw attaching the top center of the heater case to the dash panel.
6. Remove two (2) screws attaching the right end of the heater case to the dash panel, and remove the heater case from the vehicle.
7. Remove nine (9) screws and one (1) bolt and nut attaching the heater housing plate to the heater case, and remove the heater housing plate.
8. Remove three (3) screws attaching the heater core frame to the heater case and remove the frame.
9. Remove the heater core and seal from the heater case.

To install:

1. Position the heater core and seal in the heater case.
2. Install the heater core frame (3 screws).
3. Position the heater housing plate on the heater case and install the nine (9) screws and one (1) bolt and nut.
4. Position the heater case to the dash panel and install the three (3) attaching screws.
5. Working in the passenger compartment, install two (2) nuts to retain the heater case and plenum right end to the dash panel.
6. Connect the heater hoses to the heater core. Tighten the hose clamps.
7. Connect the wires to the blower motor resistor assembly.
8. Connect the blower motor wires.
9. Position (slide) the self-adjusting clip on the temperature cable to a position approximately one 1 inch; (25.4mm) from the cable end loop.
10. Snap the temperature cable on the cable mounting bracket of the heater case. Then, position the self-adjusting clip on the door crank arm.
11. Adjust the temperature cable.
12. Check the system for proper operation.

Check all your ac/heater fuses. there are some on the side of dash and some under hood. some vehicles have a fuse that runs the high speed blower operation. there may be several in each location, so check carefully.

The temp blend door rotates between allowing heat through the heater core, or cold air through the a/cevaporator, or a blending of the 2 by being anywhere between the two.

I would check the heater a/c control head first and hope it's just the control head.
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here is a descripton of the system.

Section 12-03A: Air Conditioning, Heater System, Manual, Ranger and Explorer 1996 Ranger and Explorer Workshop Manual
DESCRIPTION AND OPERATION A/C-Heater System, Manual The manual air conditioning/heater system used in these vehicles is a split-case, blend air design. This design includes the following major components:

• An A/C evaporator housing (19850) which is attached to the engine compartment side of the dash panel (01610). This assembly includes: (1) the A/C evaporator core (19860), (2) the suction accumulator/drier (19C836), (3) the A/C cycling switch (19E561), (4) an internal, A/C evaporator core orifice (19D990) located inside the inlet line to the A/C evaporator core, (5) a blower motor (18527), (6) a blower motor wheel (18504), (7) a heater blower motor switch resistor (18591), and (8) the A/C evaporator case (19897).
• A heater air plenum chamber (18471) which attaches to the passenger compartment side of the dash panel. This assembly includes: (1) the outside/recirculating air inlet door, (2) the panel door, (3) the floor defrost door, (4) the temperature blend door, and (5) the heater core (18476).
• Other components which link and/or control the heating and air conditioning systems include: (1) the A/C control (19980), (2) the ducts and registers, (3) the windshield defroster hose nozzle (18490), (4) the control cables, (5) the vacuum lines, (6) the refrigerant tubes and hoses, (7) the A/C compressor (19703), and (8) the A/C condenser core (19712).

The A/C control (19980) assembly consists of three main parts:

• The function selector knob, a vacuum selector valve combined with an internal electrical switch.
• Heater blower motor switch (18578), an electrical switch that provides four speeds of A/C blower motor operation.
• A temperature control knob, which controls the position of the temperature blend door mounted on A/C evaporator housing (19850) assembly.

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Temperature Control
The temperature selector actuates a variable resistance switch. This switch varies the voltage to an electric actuator used to position the temperature blend door. Positioning the temperature control in any position between COOL and WARM causes the temperature blend door to direct more or less outside air through or around the heater core (18476) for whatever proportion of heated or unheated outside air is desired. The air blends together as it leaves the heater core and enters the heater air plenum chamber (18471) for distribution.
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System Airflow Description Air is drawn into the system by the blower motor (18527) through the outside-recirc. door opening. The air is blown through the A/C evaporator core (19860) and then the heater core (18476) (when the temperature control is moved toward the WARM position). When the temperature blend door is in the maximum COOL position, the air bypasses the heater core. When the temperature control is moved to the right, away from the maximum COOL position, air passes through the heater core where it is warmed, and then mixed with the cool air before it is discharged through the registers. OFF
With the function selector in the OFF position, the outside-recirc. door is in the recirculated air position. It is closed to outside air and no air passes through the system. The blower motor is off. MAX A/C
NOTE: No temperature modulation is possible in the MAX A/C position.

In the MAX A/C position, the outside-recirc. air door is in the recirculated air position. All of the air discharges through the panel registers except for a small amount of floor bleed. The A/C compressor (19703) operates in this function control setting.
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You have to almost remove the dash to get this part out.
Removal

1. Disconnect battery ground cable.
   

1. NOTE: Refer to Section 01-12 for instrument panel removal and installation procedure.
   
   Loosen instrument panel (04320) and pull back from cowl.
   

1. Remove A/C electronic door actuator motor electrical connector from bracket on A/C evaporator housing.
   

1. Remove three A/C electronic door actuator motor retaining screws.
   

1. NOTE: The mounting bracket remains in place on the A/C evaporator housing.
   
   Lift A/C electronic door actuator motor vertically approximately 12mm (1/2 inch) to disengage it from bracket and actuator shaft, then pull A/C electronic door actuator motor back toward passenger compartment.
   

it is the heater core ask auto zone to help u out