I think that the servo controlled temperature door is sticking in the closed position. We can turn the dial on the temp selector to warm things up a bit & no change occurs. After messing with the controls for awhile you will eventually hear a "pop" & the heat will start working. I think the "gate" or "door" is sticking but don't know where it's at. My g-friend thought she heard the pop under the drivers side of the dash. ?

First check your coolant level. If the coolant system is full, then it is probably the passage doors inside the heater/AC case not operating properly. A door or its actuator has a malfunction. Most actuators are vacuum controls, although some are electric motor operated. Turn Heater on and set temp. control on high-this should cause the actuators to respond by opening some inner doors. So when you turn the blower on, air is forced across the heater core (the little coolant filled "radiator" in the case), and warm air comes out the vents. Watch or listen for the actuators to respond when you use the heater controls. There may be several actuators on the heater case, situated all around, but they are on the outside of the case, right near the inner door they operate.

With the AC, I wouldn't get in a hurry. You can rack up alot of money real quick trying to solve an intermittent problem with an AC system and not solve the problem at all. Be patient, and wait til the problem area goes completely, then you will know exactly what to replace.

Sounds like the blend door is stuck in the heat position OR the temperature controller is not operating the hot water valve.

I would say either blend door issues or a vacuum control valve, heater control valve or a vacuum hose to the heater system is leaking. I would start to suggest. You are correct in checking the blend door. A computer scan should tell you what temp the climate control thinks it is in the passenger compartment. It may be a thermostat problem giving the climate control a false reading. Your blend door is controlled by a servo motor under the dash. You can remove the servo and watch to see if it moves when you change the temp setting from heat to cool. Also, you should be able to manually move the door to the heat position and see if you get heat.

you have to replace the blend (heat/cold) door motor, you can try to remove motor and turn door and try to jam something in door handle slot ,that the part that the motor turns,hope this helps.

Hi...
Perform the following basic Checks and Information
1. Check Drive Belts,If belt is intact proceed to the next step.
2. Check for Compressor Clutch Engagement - Turn the air conditioner to the "on" position and set controls to the coldest setting. Start the engine and allow to idle. Then open the hood and inspect the clutch at the front of the compressor, is it turning? "Engaged" if so, the system has enough refrigerant to activate. If the system is low on refrigerant it will not work properly. In this case an air conditioner recharge kit is needed to recharge the system. If the compressor clutch is not turning proceed to next step.
3. Inspect for Refrigerant Leaks
4. Check under dash panel and under hood power distribution center
5. Check Temperature Control Vents - The vents inside your car are controlled by a cable, electrical servo or vacuum servo. If the vent door is not functioning properly it will cause warm air from the heater to exit the vents. To check this start the car and allow the engine idle, next turn the blower motor speed on low, switch the temperature control from warm to cold while your ear is close to the vents. You should hear the door move inside the heater box as it swings from open to close. If not, inspect for a vacuum leak or a shorted motor in the servo, repair the leak or replace the servo motor.
Thanks
Smith

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.
   

First, feel the heater hoses going into the firewall under the hood. If they are hot, then you have hot engine coolant going into the heater core. If they are not hot, then you either have a bad thermostat or you are very low on engine coolant.

Next you need air flowing through the heater core so it can come out heated through your vents. If the iar is flowing somewhere else, your temp blend door is not moving because the bend door motor is bad or your temp knob on your heater controls is bad. The blend door motor is an electric motor.

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Air Flow Control
Air flow control is accomplished in the following manner:

• Primary control is through the function selector knob , mounted on the heater function selector switch, which is part of the heater control .
• The function selector knob has the following positions: OFF, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST.
• The heater function selector switch combines a vacuum selector valve with an internal electrical switch.

• The vacuum selector valve directs source vacuum to various vacuum control motors (18A318) . Refer to the System Airflow Schematic and Vacuum Control Charts.
• An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor switch (18578) .
• The position of the function selector knob determines the manner in which the system will operate.
• Each position of the function selector knob is detented for positive engagement.

Temperature Control
The temperature control operates in the following manner:

• Temperature control of the heater system is determined by the position of the temperature control knob (between COOL-BLUE and WARM-RED) of the heater control .
• This control knob is connected to a potentiometer mounted in the heater control . This potentiometer is electrically connected to the electric blend door actuator that operates the A/C air temperature control door.

• Movement of the control knob from COOL (Blue) to WARM (Red) causes a corresponding movement on the air temperature control door and determines the temperature that the system will maintain.

System uses a reheat method to provide conditioned air to the passenger compartment.

• All airflow from the blower motor (18527) passes through the A/C evaporator housing .
• Temperature is then regulated by reheating a portion of the air and blending it with the remaining cool air to the desired temperature.
• Temperature blending is varied by the air temperature control door, which regulates the amount of air that flows through and/or around the heater core (18476) , where it is then mixed and distributed.

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inside you plenum box:

the door opening & closing on Max a/c is the inside/outside air intake door.
The temp blend door is the one you are concernd about. It says you have to remove instrument panel for access. ouch!!!

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A/C Electronic Door Actuator Motor
The A/C electronic door actuator motor (19E616) is located on top of the A/C evaporator core housing assembly.

• Its function is to move the A/C air temperature control door on command from the control assembly.
• The A/C electronic door actuator motor contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the A/C air temperature control door.
• Battery voltage is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The actuator wiper voltage is sent to the control module and matched with the wiper voltage of the module potentiometer. The printed circuit board then drives the actuator motor in the direction necessary to make the actuator wiper voltage agree with the control module wiper voltage.

No Blower in Floor Mode
A customer arrives with a 1983 to 1995 Full Size Ford, Lincoln, or Mercury
automobile with automatic temperature control. If the complaint is no blower operation when
the floor mode is selected, the vehicle may have a problem with the thermal blower lockout
switch also referred to as the CELO (cold engine lock out switch).
The thermal blower lock out switch is located in the heater core intake hose. The two
wire switch has a thermal element with a small set of contacts, the contacts are open when the
coolant is below 120°F and closed when the coolant is above 120°F. The thermal blower lock
out switch also contains a vacuum switch, which applies vacuum to the outside/recirculate
valve when the system is in the floor position. When the engine coolant is below 120 degrees
and the selector is set to floor position, the thermal blower lock out prevents blower from
turning on and closes off the outside air during engine warm-up. When the coolant
temperature is above 120 degrees, and the selector is set to the floor position, the thermal
blower lock out switch allows the blower to operate and opens the outside air door.
In order to diagnose this problem, test the thermal blower lockout switch with the
engine at normal operating temperature (above 120°F). Unplug the wire harness connector
from the thermal blower lockout switch. Using a 15-amp fused wire, jumper the harness
terminals to test the switch. If the blower comes on, the thermal blower lock out switch is
faulty. If the blower doesn’t come on, look for an open between the control head selector and
thermal blower lock out switch.
In some cases the blower may continually run even when the engine temperature is
below 120 degrees. Unplug the thermal blower lock out switch and if the blower motor turns
off, the thermal blower lock out switch is faulty. If the motor continues to run, look for a
short to power between the control head selector and thermal blower lock out switch