Category: Air conditioning air flow

Condenser fan assembly

What is the purpose of the radiator fan assembly ?

The purpose of the fan is to maintain adequate airflow through the radiator and condenser core, especially at low vehicle speeds and when the engine is idling, sitting still. The fan is used to speed up the natural draft through the radiator/condenser or create one if the vehicle isn’t moving.
At high motor vehicle speeds the ram effect through the air is usually sufficient enough to cool the radiator/condenser core so the fan is not required.

Three important things may happen to the refrigerant in The Condenser and we need the radiator fan assembly working at maximum efficiency for The Subcooling process to happen properly:

  1. The hot gas from the compressor is desuperheated from the hot discharge temperature to the condensing temperature. The hot gas from the compressor may be 200 °F or hotter on a hot day on an air-cooled system.Desuperheating is accomplished in the beginning of the coil.
  2. The refrigerant is condensed from a vapor to a liquid. This is latent heat transfer. This is done in the middle of the coil, the only place that the coil temperature will correspond to the head pressure.
  3. The liquid refrigerant temperature may then be lowered below the condensing temperature, or SUBCOOLED.The refrigerant can usually be subcooled to between 10 °F and 20°F below the condensing temperature.

Condensers have a relationship to the temperature of the air passing over them. For instance, the refrigerant inside the coil will normally condense at a 30°F higher temperature than the air passing over it.

The four major components that make up the air conditioning system are:

  1. The evaporator
  2. The compressor
  3. The condenser
  4. The refrigerant metering device.

The evaporator absorbs heat into the system. When the refrigerant is boiled at a lower temperature than that of the substance to be cooled, it absorbs heat from the substance.
The compressor: is the heart of the refrigeration system. It pumps heat through the system in the form of heat-laden refrigerant. A compressor can be considered a vapor pump.
The condenser: rejects both sensible (measurable) and latent (hidden) heat from the a/c system and delivers subcooled refrigerant to the metering device. This heat can come from what the evaporator has absorbed any heat of compression or mechanical friction generated in the compression stroke, and any heat absorbed by superheating the refrigerant in the suction line before it enters the compressor.
The refrigerant Metering Device: The expansion device is one component that divides the high side of the system from the low side (The compressor is the other).It is responsible for metering the correct amount of refrigerant to the evaporator. The evaporator performs best when it is as full of liquid refrigerant as possible with none left in the suction line.


What is a car ac condenser?
The condenser is one of automobile heat exchangers and operates much like the radiator.
The condenser receives the hot gas after it leaves the compressor. The discharge gas from the compressor is a high-pressure, high-temperature, superheated vapor. The temperature of the hot gas from the compressor can be in the 200°F range and will change depending on the surrounding temperatures. Condenser designs have changed over the years, but there have been 3 main types. They are:
Tube and fin condenser
Serpentine tube condenser
Parallel flow condenser

A/C blowing hot air.Why?

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.


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.

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.

a/c air flow controls

The Hvac Blower motor resistor.


The function of a blower motor resistor.

The function of a blower resistor is to slow down the blower various speeds by way of a voltage drop.

In the high position, the resistor is bypassed by a relay on many systems and full voltage is supplied to the motor. There are multiple resistance taps on the resistor block that make up each speed. 

Resistance, voltage drop and blower speed.

The more resistance, the greater the voltage drop and the lower the blower speed .