Why my car A/C is stuck in heat mode when the cooling mode is on?

 

A malfunctioning Temperature Blend Door Actuator Motor could be the cause. When the Winter Season begins, and you try to change the A/C settings on the Air Conditioning Climate Control from Cold air to hot air and you cannot control the air temperature.

 

What is a blend door actuator?

CALLOUT	COMPONENT NAME
2	Temperature Blend Door Actuator Motor

 

 

The blend door actuator is a small electric motor. As you adjust the temperature up and down, the signals go through the actuator to complete the request, positioning the air door on the right position.

When A/C became a popular option on vehicles in the mid to late 1970s, the systems were simple, except for some high levels vehicles, which were often the test bed of things to come.

The control systems were cable actuated, and eventually, vacuum controls were introduced. Most systems were equipped with a heater control water valve, also cable or vacuum controlled.

Automatic temperature control systems had a range of controls: vacuum, electromechanical, and pure electronic devices. They were complicated for the time and often not reliable.

MANUAL CONTROL SYSTEMS

The air delivery system controls the movement of heated and cooled air into and throughout the passenger compartment. The Hvac housing is the plenum unit located and beneath the instrument panel. It contains the evaporator and heater core, and the blower motor assembly and the blower speed control device.

The plenum houses the air doors and door actuators that direct airflow to the correct ductwork. The doors ay be controlled by cables, vacuum, or electrical actuators. Single zone systems are usually equipped with three doors:

 

The Blend Door Actuator – the blend door determines the temperature of the air flowing through the passenger compartment. If the A/C is operating, the air is dehumidified and cooled. The more air the blend door directs through the heater core, the warmer the air entering the passenger compartment.

DUAL ZONE A/C SYSTEMS

Dual zone systems operate in the same manner as single zone systems. However, most dual zone systems use two blend doors: one for the driver side and the other for the passenger side. This design allows for separate temperature settings on each side for the vehicle.

 

DIFFERENT TYPE OF ACTUATOR MOTORS

Actuator motors used in automotive Hvac systems can be one of four designs, depending on vehicle manufacturer, system design, year, and model of the vehicle:

• Tri-state
• Bi-directional
• Three wire
• Two wire

Tri-state Actuator

CALLOUT	COMPONENT NAME
2	Temperature Blend Door Actuator Motor

 

A tri-state actuator is a five-wire design. Three of the five wires are used for the feedback circuit. The other wires are for ignition voltage and Hvac control head requests.

0 volts will move the motor one way, 5 volts will drive the motor in the other direction, and when the signal wire reads 2.5 volts, the motor stops rotating.

Bi-directional Actuator Motor

Bi-directional actuators use three wires for circuit feedback. The other two wires are the positive and negative circuits that drive the motor. These circuits are controlled by the Hvac control head and move the motor direction based on the selections made at the control head.

CALLOUT	COMPONENT NAME
2	Temperature Blend Door Actuator Motor

Three Wire Actuator Motors

Three wire actuators have a power, ground, and an input wire from the Hvac control head. These actuators use a preprogrammed logic chip containing all the information to drive the motor in the requested direction. When a position change is requested by the vehicle operator, a circuit in the control head sends voltage to the actuator motor. As the motor moves, a potentiometer in the actuator compares the motor voltage to the output voltage from the control head. When both voltage readings are the same, the actuator motor stops. There is no feedback to the control head with this design.

Two Wire Actuator

CALLOUT	COMPONENT NAME
3	Temperature Blend Door Actuator Motor

 

Two Wire actuators create electrical pulses when the commutator rotates across the brushes of the motor. The Hvac control head, which has pre-programmed logic and actuator endpoint references, counts the electrical pulses as the motor moves the door through its sweep from one end to the other end. The actuator endpoints will change as the door seal wears, so if the endpoint counts become too large, a DTC will be set. If the Hvac system loses power, or if a component is replaced, the endpoints must usually be relearned through a calibration process.

SYMPTOMS OF BAD BLEND DOOR ACTUATOR

How do I know if my blend door actuator is bad?

Binding Actuators

If an actuator binds inside the Hvac plenum, the control module will attempt to overcome the restriction several times before it shuts down the circuit. You will hear the ticking noise. If the binding clears on the next activation, the control module will perform a calibration and set a history DTC.

 

What does a bad actuator sound like?

If an actuator binds inside the Hvac plenum, the control module will attempt to overcome the restriction several times before it shuts down the circuit. You will hear the ticking noise from the actuator motor.

Where is the heater blend door actuator located?

The Blend Actuator Motor is located on the Hvac Box underneath the dashboard. The exact location of the Actuator will depend on the Make, Model and Year of the vehicle serviced.

CALLOUT	COMPONENT NAME
1	Left temperature actuator screws
2	Temperature blend actuator
3	Left temperature actuator lever
5	Hvac Box

2015 Cadillac CTS Coupe RWD V8-6.2L SC

How do you test a blend door actuator?

Actuator diagnosis

When diagnosing Hvac actuators, always check the door for binding or restriction, caused by a distorted, worn, or damaged plenum. Check for restrictions that may be caused by a foreign object that is lodged in the door seep, or a broken crank arm on the door assembly.

Do not operate an actuator that is not attached to the door on the plenum. If the door is not attached, the motor can drive past its limits, which usually results in damage to the actuator.

What tools to use for door actuator diagnostics?

Actuator motor operation can be checked with a digital multimeter. Using service information and wiring diagrams for the vehicle, find the correct connector pins for feedback, power, and ground circuits on the actuator. Carefully back probe at the pins, taking care not to pierce the wiring insulation or cause damage to the connector pins. With the meter set on the DC volts scale, move the Hvac selector know and watch for a voltage change as the door position is commanded to change. There should be a voltage change as each position is selected.

• Digital Multimeter
• Service Information and Wiring diagrams
• Scanner

These voltage readings will not give the exact position of the door. However, they will indicate that the door is moving through a complete sweep from one endpoint to the other.

How long does it take to fix a blend door actuator?

The labor time will be different depending on the make, model, and year of the vehicle and if it is a dual zone system or single. The labor will increase because of the time needed to remove all components before we can gain access to the actuator. In some model’s complete removal of the entire dashboard is needed to gain access to the Blend door actuator motor.

 

2015 Dodge or Ram Truck RAM 1500 Truck 2WD V6-3.0L DSL Turbo

Temperature blend door motor

Left side: 0.5 hours

Right side: 5.2 hours

 

2013 Ford Focus 2.0L

Temperature blend door motor replacement

Driver side: 0.5 hours

Passenger side: 0.5 hours

Do you need assistance with the A/C Blend door actuator replacement or calibration in your car?

Call Us Today !  One of our ASE certified car a/c mechanics will come right to your home or office for a check up and installation.