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Heater 101

Winter is here a little earlier than expected and with that comes the chance of your heater system not functioning properly. We have all been there. The first real cold morning comes along, and we patiently wait for our car to warm up, so we can turn on the much-welcomed heater and BAM, cold air. Something within our heater system has failed and that is not ok. Here is a little guide to understanding what might be happening and some suggestions on how to fix the problem.

A car’s heater and heater core are part of the engine cooling system, though the heater does not provide the removal of heat from the engine as the normal function. It is meant to provide in-car passenger comfort during the cold winter months. The heater core is mounted in the air distribution duct system and is usually under the dash area of the front passenger side of the vehicle. The heater core resembles a small radiator and functions as a heat exchanger with the engine coolant flowing from the top of the engine through the heater core and back to the water pump in most designs. Engine heat is picked up by the coolant through the process of conduction and is transferred by convection to the cooler outside air passing through the heater core to the vehicles interior. An electric blower motor is used to force air through the heater core. This provides a ready source of heated air to be used to improve passenger comfort when needed. In some systems the engine coolant is constantly flowing through the heater core any time that the engine is running, whereas in other systems a control valve is used to stop the flow of coolant when heat is not needed.

Most failures of the heater core are due to a leak. This is easily detected by noting a wet floor carpet just below the case on the passenger side of the vehicle or if fogging of the windshield is occurring (moisture coming in from ducts). Replacement of the heater core, unfortunately, is not so simple. Because of the many different variations of installation, it is necessary to follow the manufacturer’s shop manual instructions for replacing the heater core.

The following is a typical procedure only and is not intended for any particular make or model vehicle:

  1. Remove the coolant
  2. Remove the access panel or the split heater/air conditioning case to gain access to the heater core
  3. Loosen the hose clamps and remove the heater core hoses
  4. Remove the cable and vacuum control lines (if equipped)
  5. Remove the heater core, securing brackets and clamps
  6. Lift the core from the case

The heater control valve regulates the flow of coolant through the heater core to control core temperature by opening and closing a passage to increase or decrease flow. The heater control valve may be in the inlet or outlet to the heater core. When the control valve is open, a portion of the heated engine coolant circulates through the heater core. The heater control valve may be cable operated, vacuum operated, or operated by a bidirectional electric solenoid or motor. The control valve depending on the valve position selected, meters the amount of heated coolant that is allowed to enter the heater core, from full off, to full flow. The HVAC control panel temperature selector regulates the operation of most heater control valves, whether actuated by a cable, vacuum diaphragm, or electrically energized. Some heater core assemblies have a mechanical heater control valve integrated into them to regulate coolant flow through the core. Other than a leak, which is usually obvious, the valve fails due to rust or corrosion. To replace the valve:

  1. Remove the coolant to a level below the control valve
  2. Remove the cable linkage, vacuum hose, or electrical connector from the control valve
  3. Loosen the hose clamps and remove the inlet hose from the control valve
  4. Remove the heater control valve as applicable. Remove the outlet hose from the heater core. Remove the attaching brackets or fasteners from the control.
  5. Inspect the hose ends removed. If they are hard or split, cut 0.5 to 1 inch from the damaged ends. The better thing to do is replace the hoses.

 

Heater hoses and clamps are basically about the same as radiator hoses and clamps except they are generally smaller in diameter. It is a practice of some technicians to use a hose that is too large for the application and overtighten the hose clamp to stop the leak. A hose clamp that is too large for the hose is often distorted when tightened sufficiently to secure the hose.

Heater hoses are replaced in the same manner as radiator hoses. It is much easier to use the wrong size hose, however. For example, a ¾ in. hose fit very easily onto a 5/8 in. fitting. The hose clamp then must be overtightened to squeeze the hose onto the fitting sufficiently to prevent a leak. It is not so easy to slide and 5/8 in. hose onto a 5/8 in. fitting. The intent, however, is to use the proper size hose for the application. It is a goo practice to replace all heater hoses if any are found to be defective. The following is a typical procedure:

  1. Remove the coolant to a level below that of the hoses to be replaced
  2. Loosen the hose clamp at both ends of the hose
  3. Turn and twist the hoses to break them loose
  4. Remove the hose. Do not use unnecessary force when removing the hose end from the heater core.

As with cooling system hose clamps, heater hose clamps should be replaced when a hose is replaced. It is most important that the proper size clamp be used for the hose. If the clamp is too large, it will be distorted before being tightened enough to secure the hose onto the fitting. When this occurs it is extremely difficult to stop a leak. Make sure you test your coolant every six months. You can do this with Phoenix Systems Coolant Test Strips.

CoolantStrip 100 Coolant Test Strips

$43.99

CoolantStrip is a New test strip used to determine when to correct or replace your coolant. CoolantStrip is recommended for use with all coolant colors. Changing your coolant when needed will help prevent breakdowns, improve safety and extend the life of critical engine components.

 

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