About Car Heaters

Car heating systems have been around since soon after Henry Ford introduced the Model T. Over the years, there have been numerous advances in the heating systems to include the different distribution methods to different levels of the dash for better passenger comfort. Better control over the level of heat as well as source of introduced air adds to passenger comfort. The air source can be changed to recirculated air or vented air from the atmosphere.

Types

The most basic heating system is manually operated through the control head. The switches include:

1. The fan switch--this has four positions relative to fan speed
2. The temperature control--this, when turned, will either increase heat or reduce heat
3. The position switch--this dictates where the air will escape from the dash, either from the floor, dash, or defroster and usually a position for a combination of any two positions. The air escapes from the dash only.

The next type of heating system is the automatic climate control. It utilizes two or more temperature sensors to keep the temperature constant. To activate the system the automatic button is pushed and the desired temp is adjusted with an up or down button. The desired position of the escaping air is also adjusted with a button. The system usually has a set of vents between the front seat, and in some cases, above the headliner to move air to the rear seat position. When the door is open, most units will increase fan speed to maintain temperature control and slow when it is closed.

Upgrades

Dual climate control is one of the newer innovations wherein the driver and passenger have separate controls for the level and intensity of the heat discharge to their individual seat position.

Many of the larger vehicles will offer the option of dual air and heat where there is a totally separate heating system in the rear of the vehicle. The rear heat and air conditioning can be adjusted by the rear passengers in accordance to their needs.

Function

The heater's function starts with the hot water. It is picked up from the vehicle's water pump and transferred through a hose to the inlet side of the heater core. The hot water passes through the heater core and out the other side where the water is transferred back to the intake manifold or top of water pump. The heater core is always hot although the heat transfer to the interior of the car is controlled by a series of doors within the heater core housing under the dash. This housing contains the air conditioning evaporator as well.

Door Control

The doors are controlled by the control head on the dash. The doors are operated by one of two methods. The first is by vacuum. The vacuum is picked up from the engine intake manifold and transferred through a tube to the control head on the dash. The control head transfers the vacuum from the feeder tube to individual vacuum motors on the air conditioning and heating housing under the dash. These vacuum motors, when vacuum is applied, simply move an arm in or out to change the position of the doors. The doors work the same in all types of systems, the only thing that changes is the type of motors from vacuum to electric. The heater and air conditioning blower under the dash also remains the same except the complexity of the control panel. The speeds for the fan motor are controlled in all cases by a blower motor resister. In most cases this is located in immediate proximity to the blower motor. It controls the fan speed by supplying a varying resistance to ground.

Problems

If the fan does not work check the fuse first. If the fuse is good, pull the connector off of the blower motor under the right side of the dash and check the connector to it with a regular test light. With the key on, there should be power to the blower. If there is no power at the connector, put the connector back on and pull the connector on the heater blower motor resister and check for power. If it has power replace the blower motor resister and if it had no power replace the control head.

If the positions of the air discharge can not be changed to any position the control head needs to be replaced. If all but one position can be changed remove the glove compartment and look at the motors on the housing that is visible with the glove box removed. With the key on, move the control panel functions and watch each motor function by moving in or out. Check for a vacuum on the motor that does not move. Check with the engine running or in the case of an electric motor check for power. If either one has a source, be it vacuum or electrical than the motor is bad. If no source and a good fuse then the control panel is malfunctioning and needs to be replaced.