We need to make sure what is the sequence of events here, because the cause could be different.
After car startup A/C blows hot then sometimes blow cold.
- A/C Climate Control faulty
- Blend door stuck
- A/C Actuator motor Faulty
What does an AC actuator do?
The AC actuator moves air distribution doors to two or more positions to direct air flow for heating and A/C vents. The AC actuator is located underneath the dashboard attached to air distribution doors in the hvac box.
Doors can control hot air/cold air blending, recirculated/fresh air control, or dual zone splitting. The motors can move the doors into many different positions, or just two.
What are the symptoms of a bad actuator?
Air coming out from the wrong vents, clicking noises coming from behind the dashboard or not being able to control the temperature(Climate control set on cold position but blowing hot air) or re-circulated or fresh air mode in your car is a sign of a bad air door actuator motor. Exhaust or outside road fumes inside the cabin.
What are the symptoms of a bad temperature blend door actuator?
Air conditioning temperature can’t be regulated. The driver, passenger or both, depending on the design won’t be able to control the temperature on their climate zone. Decreased air conditioning performance due to improperly mixed of hot and cold air inside the hvac box.
How to test the blend door actuator motor?
There are some simple tests that could be done in order to determine if the vehicle is having issues with the blend door actuator:
If you can’t set the temperature from the head control set selector, there is a problem with the blend door actuator, the blend door, the head control set or the circuit connecting them.
For every movement of the knob on the climate control set corresponds a movement on the blend door. If there is no movement, there is a problem with the blend door actuator, the blend door, the climate control set or the circuit connecting them.
As the blend door open or closes to the heat or cold position it opposes the flow of air coming from the blower motor and makes a change in the intensity of the air noise. If you can’t hear this change in air noise intensity there is a problem with the blend door actuator, the blend door, the climate control set or the circuit connecting them.
After car startup A/C blows cold then sometimes blow hot.
- Low refrigerant charge
- A/C restriction on the high side of the system
- A/C cycling switch faulty
- Dirty evaporator core
- Dirty in-cabin air filter
- Air bypass
- Faulty evaporator temperature sensor
- Faulty A/C compressor clutch coil
The low-pressure / temperature sensor will interrupt compressor operation if system pressure drops to the point that a loss of refrigerant charge to the compressor occurs.The high-pressure cut-out sensor interrupts compressor operation in case of extremely high system pressure.
Cycling clutch pressure switch controls compressor pressures operation.It keeps the refrigerant pressure between 47 psi-26 psi.This cycling action maintains the evaporator at 33 °F.
Some air conditioning systems use a thermostatic clutch cycling switch that cycles the compressor on and off in relation to evaporator outlet temperature.