Cars & Trucks - How Max A/C works and saves you Gas

Hi John,
Your right with your diagnostics, you have a blend door problem. If your switching to cool air and it is still hot then you also have a heat exchange unit fault, this is the component that changes the water flow from hot to cool by shutting off. If it is not operating correctly this will give you constant hot air no matter where you temperature switch is positioned.
As for the warm air while the engine is cold, sounds like the blend door is still open to atmosphere tempreture and if it is hot outside will pull that hot air into the inside of the vehicle.
Have the heat exchange valve checked, and the only way the check blend door operation is to remove the wiring from the blend doors and have the circuit tested. If the circuit is ok then the blend doors will need to be replaced.
Hope this helps

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.
   

According to the shop manual you do not have one.
Air Distribution and Filtering Printable View (79 KB) NOTE: The air distribution system of this vehicle cannot be equipped with a cabin air filter.
There are 2 sources of air available to the air distribution system:

• Outside air
• Recirculated air

Recirculated air is automatically used when the electronic manual temperature control mode selector is set in the MAX A/C or OFF modes and can be selected in any mode other than MAX A/C, OFF or DEFROST by selecting the RECIRC button. Recirculated air is available in all modes except DEFROST. If the vehicle is equipped with an electronic automatic temperature control (EATC) system, recirculated air is used in OFF and is available in all modes except DEFROST. RECIRC mode is a timed function in FLOOR and FLOOR/DEFROST.
Air distribution within the vehicle is determined by the electronic manual temperature control (EMTC) function selector switch position, or is controlled by the EATC system in the AUTOMATIC mode. The air distribution mode on EATC vehicles may be overridden by the driver if desired. Air distribution doors are used to direct airflow within the heater core and evaporator core housing and the plenum chamber. An electronic mode door actuator is used to position these air distribution doors. One air inlet mode door is used to switch between FRESH or RECIRC air inlet. An electric actuator is used to position the air inlet mode door.
Air enters the passenger compartment from the:

• instrument panel A/C registers.
• heater outlet floor ducts.
• windshield defroster duct.
• side window demisters.
• center flow-through console (if equipped).

Passenger compartment air is exhausted from the vehicle through open windows or body air vents.

If your blower motor is in the engine compartment, I suspect you did not get a good seal around the housing when you reinstalled it. Usually a foam gasket.
For now, push the recirc button so you are drawing air from inside the car into you heater system. Recirc doesn't work on defrost or floor/defrost.

The exhaust leak is almost always broken studs on the exhaust manifolds. It makes a tick noise when cold and usually goes away when the engine warms up. After a year or so, the noise doesn't go away.

Your heater-a/c air intake is at the base of the windshield through the screen on the passenger side. WHen the exhaust leaks from the manifold, the exhaust gas gets sucked into the air intake.
You can put the heater in recirc mode and it will draw air in from inside the car instead of though the outside air intake. You can't leave it in recirc for long in winter or your car will get ice or fogging on the windows from too much humidity. Take it off recirc after 10 minutes.

See this iste for more info

http://autos.groups.yahoo.com/group/villagerquest/