Heater and AC

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How the Heater and Air Conditioning Systems Works

- We will add links to other pages in our site that explain how to replace each component with a step by step guide enhanced with pictures.

- Heater system, how does it work?.... The heating system in your vehicle is composed of several items, heater core, heater hoses, heater control valve, heater controls and cables, heater box, heater blower motor, heater vents, engine coolant, radiator.

- The heater core is located inside the heater box, the heater hoses connect the heating system to the vehicle's cooling system, which allows hot coolant to circulate inside the heater core, the valve that controls the amount of coolant circulating inside the heater core is the heater control valve, this valve is activated when you turn your heater control to hot in your dashboard, a cable connects your heater control to the heater valve.  In modern vehicles, the cables have been replaced by electronic devices. 

- The heater control is also linked to the heater vents, either by cables, vacuum hoses or electronic devices, depending on the age, and make of your vehicle.

The principal is the same, and that is to give you the amount of comfort desired inside the vehicle, allowing you to control the amount of heat that enters your cab, and weather is directed to the windshield, the floor, or the vents on the dash.

- The air is forced by the heater blower motor, this motor is usually located on the firewall of the vehicle near , on top or mounted on the side of the heater box, it usually has 4 speeds that are controlled by the heater control knob.

- The air passes through the heater core, and because the heater core has hot engine coolant circulating inside, the air comes out hot.  Modern vehicles with automatic heater controls are linked to either their own electronic control module, or are linked to the engine control computer, in either case, the electronic controls are activated automatically by the control module to direct the correct amount of air through the vents to give you the temperature you requested.

- Older air cooled vehicles like Volkswagen beetles have a very simple heater system, the air that comes through the vents is air that comes out directly from the engine compartment, the same air that circulates around the engine to cool it down is redirected to the vents by cables linked to the heater control knobs.  This system may not be the most efficient, but for the most part it works well

AIR CONDITIONING SYSTEM: The air conditioning system is composed of several items: AC compressor, AC hoses, evaporator,Dryer, AC condenser, AC blower motor ( same motor for heater and AC). REfrigerant (Freon) either R12 or 134a depending of the age of the vehicle, orifice tubes, AC controls.

- The cold air that comes inside the cab through the vents is forced by the blower motor, the AC system and heater system share the same vents and the same blower motor, very few vehicles have dual motors, one for AC and one for the heater.
- The reason why the air comes out cold is because inside the dash usually in the same box where the heater core is located there is an evaporator core ( like a reverse heater core), The refrigerant inside the evaporator is cold because it has been compressed by the AC compressor, the AC compressor is driven by the engine,as the refrigerant  passes through the evaporator, it absorbs the heat from the inside the cab as the air passes through it. 
The refrigerant exiting the evaporator is directed through AC hoses to the AC condenser, the AC condenser is mounted usually in front of the Radiator allowing the hot refrigerant to be cooled by the air that outside air that passes trough the AC condenser, that's why the electric cooling fan comes on every time you turn the air conditioning on. Once the refrigerant leaves the AC condenser, it is directed by another AC hose to the AC compressor, to be compressed and cooled even further due to the pressure.

Older vehicles have R12 refrigerant, and they can only be serviced by a certified AC technician, newer vehicles contain R134a, this refrigerant is available at the auto parts stores and it can be purchased without a license.
- There are kits available to convert older systems equipped with R12 to the newer 134A refrigerant.
Every system has to have the correct amount of refrigerant and the correct amount of lubricant to be efficient, a system that is low in freon won't  work because the AC compressor won't come on, there is a pressure switch usually located on the filter dryer ( accumulator) .
A system that has to much refrigerant is first of all dangerous, because it will have too much pressure , this will cause a rupture in the system sooner or later, it will either blow a hose or  the evaporator, causing a major leak.

If one of the orifice tubes become clogged, it can slow the flow of refrigerant in the system causing it to have increased pressure and poor performance, there are special gauges designed to read both sides of the system, the high and low side, to determine if the high pressure is caused by a clogged orifice tube or too much refrigerant.

- Just like the heating system, newer vehicles that are equipped with electronic climate controls, have electronic devices linked to the control module or the ECM , these modules are in charge of regulating the amount of air that passes through the evaporator to give you the desired temperature.

In the following pages we will show you how to replace each component with a step by step guide enhanced with pictures.

Cabin Filter
Adding Refrigerant

Click on image to learn how to replace the heater
blower motor in a BMW 325 E-30 series

  Click on image to learn how to replace the heater valve on a Ford Explorer

  Click on image to learn how to replace the climate control panel on 1994-2000 Mercedes Benz C230.

How to add refrigerant to an ac system on a 2007 VW Jetta.

  Clicked on image to learn how to add refrigerant to a 1999 Ford Explorer

 Click on image to learn how to replace the heater core on a 1989 Oldsmobile Eighty Eight.

 Click on image to learn how to add refrigerant to the AC system on a 2000 Mercedes Benz C230 compressor.