Air recirculation not working.

[EMBronco]

Here's what the WSM says. Basically, it determines what you need, not what you want. LOL


Heating and Ventilation

The heating and ventilation system:

• controls the temperature of the air inside the vehicle.
• delivers heated or cooled air to maintain the vehicle interior temperature and comfort level.
• reduces the relative humidity of the air inside the vehicle (during A/C compressor operation).

The heating and ventilation system uses a reheat method to provide conditioned air to the passenger compartment. Temperature blending is controlled by the temperature doors, which regulate the amount of air that flows through and around the heater core, where it is then mixed and distributed. All airflow from the blower motor passes through the A/C evaporator core.

This vehicle is equipped with Auto-Start-Stop and has a cabin heater coolant pump.

Cabin heat during an Auto Start-Stop operation

The cabin heater coolant pump is available on vehicles equipped with Auto Start - Stop feature. The cabin heater coolant pump provides coolant to the heater core whenever the HVAC system requests heat and the vehicle is in auto start-stop mode. Refer to the Owner's Literature, Unique Driving Characteristics for full auto start-stop enabling/disabling information.

Auto Start-Stop Deactivation Switch

The Auto Start-Stop deactivation switch is available on vehicles equipped with Auto Start- Stop feature. Auto Start-Stop deactivation switch is a momentary contact switch that includes a LED indicator. This switch is used to deactivate the Auto Start-Stop mode. Refer to the Owner's Literature, Unique Driving Characteristics, for full Auto Start-Stop enabling/disabling information.

Air Handling

There are 4 door actuators that control the HVAC system air flow into the passenger compartment:

• Air distribution
• Air inlet
• Driver temperature
• Passenger temperature

All of the door actuators contain a reversible electric motor and a potentiometer. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the contact wiper indicates the actuator door position. The HVAC control module powers the actuator motors to move the doors to the desired positions. The desired door positions are calculated by the HVAC control module based on the set temperature, in-vehicle temperature, and ambient air temperature.

When an airflow mode, desired temperature, fresh air, or recirculation mode is selected, the HVAC control module moves the actuator motor in the desired direction.

The HVAC control module sends a PWM signal to the blower motor control module to regulate the blower speed as necessary. The blower motor control module provides variable ground feed for the blower motor based on the input from the HVAC control module. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

AUTO

When AUTO is selected:

• the HVAC system operates in a manner to achieve and maintain the temperature set by the operator.
• the air inlet door actuator is automatically controlled by the HVAC module based on the temperature setting.
• the mode door actuator is automatically controlled by the HVAC module based on the temperature setting.
• the temperature door is automatically controlled by the HVAC module based on the temperature setting.
• the A/C compressor is automatically controlled by the HVAC control module based on the temperature setting. The A/C compressor does not operate if the outside temperature is below approximately 2ºC (35.6ºF).
• the blower motor speed is automatically controlled through the blower motor speed control when it receives a PWM signal from the HVAC control module based on the temperature setting, but can be manually adjusted if desired.

OFF

When OFF is selected:

• the recirculated air request button is disabled.
• the A/C request button is disabled.
• the air inlet door closes, preventing outside air and allowing only recirculated air.
• the blower motor is off.

Max A/C

When MAX A/C mode is selected:

• the air distribution doors operate simultaneously to direct airflow to the instrument panel registers. A small amount of airflow from the floor ducts are present.
• the temperature door moves to the full cool position.
• the blower motor is commanded to the highest speed, but can be manually adjusted if desired.
• the air inlet door closes, preventing outside air and admitting only recirculated air.
• the recirculated air indicator is illuminated (recirculated air forced on).
• the A/C button is illuminated.
• the A/C compressor operates if the outside temperature is above approximately 2°C (35.6°F).

PANEL

When PANEL mode is selected:

• the mode doors direct airflow to the instrument panel registers. A small amount of airflow from the floor ducts is present.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
• the blower motor is on and the speed is adjustable.

PANEL-FLOOR

When PANEL-FLOOR mode is selected:

• the mode doors direct airflow to the floor ducts and the instrument panel registers.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
• the blower motor is on and the speed is adjustable.

FLOOR

When FLOOR is selected:

• the mode doors direct airflow to the floor ducts.
• the recirculated air request button can be enabled.
• blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
• the blower motor is on and the speed is adjustable.

FLOOR-DEFROST

When FLOOR-DEFROST is selected:

• the mode doors direct airflow to the floor ducts, the defroster duct and the side window demisters.
• the recirculated air request button can be enabled, but can automatically turn off.
• blended air temperature is available. The airflow temperature can only be cooled below the outside air temperature when the A/C is commanded on.
• the blower motor is on and the speed is adjustable.

DEFROST

When DEFROST is selected:

• the mode doors direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor ducts is present.
• the recirculated air request button can be enabled, but can automatically turn off.
• the A/C is automatically commanded on and remains on until the system is either turned off or the airflow mode has changed and the A/C button is pressed.
• the A/C compressor operates as long as the outside temperature is above approximately 2°C (35.6°F).
• the blower motor is on and the speed is adjustable.

Hey Flip. Would you happen to have this same info for the manual HVAC system. I would like to learn more about how it works. It seems like no matter what I try, I cannot get heat out of the front or rear floor vents

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[flip]

Hey Flip. Would you happen to have this same info for the manual HVAC system. I would like to learn more about how it works. It seems like no matter what I try, I cannot get heat out of the front or rear floor vents

Is it no heat or air flow at all or do you have some air moving, just not much?

 

[EMBronco]

Is it no heat or air flow at all or do you have some air moving, just not much?

There is a little airflow to the front. I would estimate that when I switch to floor only, I get about 20% of the airflow to the front floor vents, 0% to the rear floor vents, and 80% comes out the defrost.

 

[flip]

Sounds like a mode door isn't working correctly based on the distribution you're getting. Has it been like this from the beginning or just start? Is it possible anything went down the defrost or dash registers?

I'm sure you've already seen the threads about how bad floor airflow is but it sounds like yours is even worse than normal. One of the ducts at the heater case could be blocked or not hooked up correctly causing the problem or mode door not sealing, opening/closing properly.

 

[flip]

 

[EMBronco]

Sounds like a mode door isn't working correctly based on the distribution you're getting. Has it been like this from the beginning or just start? Is it possible anything went down the defrost or dash registers?

I'm sure you've already seen the threads about how bad floor airflow is but it sounds like yours is even worse than normal. One of the ducts at the heater case could be blocked or not hooked up correctly causing the problem or mode door not sealing, opening/closing properly.

I took delivery about 3 weeks ago. The first week or so, the temperature was pretty warm so I didn't notice anything. When it turned cold again about a week and a half ago is when I noticed it. I would say it's probably been like this from the beginning.

I did some testing earlier this today, here are the results:

- When set to defrost only, it only blows air out of the defrost vents at all temperature settings.
- When set to the dash vents only, it only blows air out of the dash vents at all temperature settings.
- When set to the floor vents only, I estimate that 80% of the air blows out the defrost vents, 20% out of the front floor vents, and 0% out of the rear floor vents. At all temperature settings.
- When set to floor vents and defrost, their is no change in air flow from just floor vents. 80% to defrost, 20% to front floor vents, and 0% to rear floor vents. At all temperature settings.
- When set to floor vents and dash vents, I estimate that 80% of the air blows out of the dash vents, 20% out the front floor vents, and 0% out the rear floor vents. At all temperature settings. If while in this setting, I close all the dash vents, the volume to the front and rear floor vents do not change.

Based on this, I would also think that a mode door is not operating correctly.

 

[flip]

I took delivery about 3 weeks ago. The first week or so, the temperature was pretty warm so I didn't notice anything. When it turned cold again about a week and a half ago is when I noticed it. I would say it's probably been like this from the beginning.

I did some testing earlier this today, here are the results:

- When set to defrost only, it only blows air out of the defrost vents at all temperature settings.
- When set to the dash vents only, it only blows air out of the dash vents at all temperature settings.
- When set to the floor vents only, I estimate that 80% of the air blows out the defrost vents, 20% out of the front floor vents, and 0% out of the rear floor vents. At all temperature settings.
- When set to floor vents and defrost, their is no change in air flow from just floor vents. 80% to defrost, 20% to front floor vents, and 0% to rear floor vents. At all temperature settings.
- When set to floor vents and dash vents, I estimate that 80% of the air blows out of the dash vents, 20% out the front floor vents, and 0% out the rear floor vents. At all temperature settings. If while in this setting, I close all the dash vents, the volume to the front and rear floor vents do not change.

Based on this, I would also think that a mode door is not operating correctly.

That is a reasonable conclusion. We always start with verify the issue then look for TSBs or service messages followed by a visual inspection to make sure the ducts are hooked up correctly. Then it's off to scan tool work or pin point tests.

 

[Harumph]

The only was recirc will stay on is in MAX AC mode. Otherwise the system decides which in my case is always off so I get to choke down car fumes and CA smoke in the summer.

I found if pressing the recirc button when not on Max AC, the recirc works for a period of time. It will eventually turn off, but works long enough to block car fumes, etc..

 

[EMBronco]

That is a reasonable conclusion. We always start with verify the issue then look for TSBs or service messages followed by a visual inspection to make sure the ducts are hooked up correctly. Then it's off to scan tool work or pin point tests.

I'll have to take a closer look at everything this weekend and see if there is anything obvious. Thanks again for your help.

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