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Heating system service

- diagnosis

Heating system service

- diagnosis

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Common heating system problemsCommon heating system problems

• Insufficient heat.• Blower motor not working or not working on

all speeds.• Mode doors not working – system stuck in

one mode.• Too much heat – heat can’t be turned off.• Antifreeze or oil on inside surface of

windshield.• Blower motor noise.• Odor from HVAC vents.

• Insufficient heat.• Blower motor not working or not working on

all speeds.• Mode doors not working – system stuck in

one mode.• Too much heat – heat can’t be turned off.• Antifreeze or oil on inside surface of

windshield.• Blower motor noise.• Odor from HVAC vents.

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Insufficient heat – normal air volumeInsufficient heat – normal air volume• With the fan on high speed the normal

volume of air is found at all outlets.• Possible causes of insufficient heat:

– Low coolant level– Stuck open thermostat– Air in heater core– Restricted or plugged up heater core– Restricted heater hoses– Faulty blend door actuator– Faulty heat control/heater core shutoff valve

• With the fan on high speed the normal volume of air is found at all outlets.

• Possible causes of insufficient heat:– Low coolant level– Stuck open thermostat– Air in heater core– Restricted or plugged up heater core– Restricted heater hoses– Faulty blend door actuator– Faulty heat control/heater core shutoff valve

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Check the coolant levelCheck the coolant level

• Serious personal injury can result if the radiator cap is removed when the engine is hot.

• The coolant level must be checked before the engine is started.

• The radiator should be completely full on cooling systems that use overflow tanks.

• On systems that use an expansion tank the coolant level should be between the min and max marks.

• Serious personal injury can result if the radiator cap is removed when the engine is hot.

• The coolant level must be checked before the engine is started.

• The radiator should be completely full on cooling systems that use overflow tanks.

• On systems that use an expansion tank the coolant level should be between the min and max marks.

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Low radiator – normal overflow tank levelLow radiator – normal overflow tank level

• The condition here is caused by a faulty radiator cap, neck or a leak in the overflow tube.

• The radiator has several rows of empty tubes.• Air bubbles in that form in the radiator will work

their way into the heater core.

• The condition here is caused by a faulty radiator cap, neck or a leak in the overflow tube.

• The radiator has several rows of empty tubes.• Air bubbles in that form in the radiator will work

their way into the heater core.

Empty tubes Possible leaking

secondary seal

Possible leaking overflow tube

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Coolant leaksCoolant leaks

• If the recovery tank is empty and the radiator is low the system has a leak.

• Fill the radiator with coolant and connect a pressure tester to the radiator neck.

• If the recovery tank is empty and the radiator is low the system has a leak.

• Fill the radiator with coolant and connect a pressure tester to the radiator neck.

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Pressure testingPressure testing

• The pressure tester is a hand operated air pump and gauge.

• The pressure tester is usually connected to the radiator neck with an adapter.

• The pump is operated until the pressure is near the cap opening pressure – typically 15 psi.

• The system can then be examined for leaks

• The pressure tester is a hand operated air pump and gauge.

• The pressure tester is usually connected to the radiator neck with an adapter.

• The pump is operated until the pressure is near the cap opening pressure – typically 15 psi.

• The system can then be examined for leaks

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Areas to look for coolant leaksAreas to look for coolant leaks

• Water pump weep hole• Radiator • Hoses, hose connections• Heat control/shutoff valves• Freeze out plugs• T-stat housing• Heater core• Head gasket

• Water pump weep hole• Radiator • Hoses, hose connections• Heat control/shutoff valves• Freeze out plugs• T-stat housing• Heater core• Head gasket

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Heater core leaksHeater core leaks

• Since the heater core is enclosed inside the heater box you wont be able to visually inspect it.– Coolant leaks in the heater core normally work

their way down to the bottom of the evaporator case where they will drip out of the evaporator drain tube.

– The evaporator drain tube is close to the bottom of the firewall

– A leaking heater core will usually discharge a mist of coolant out of the defroster vents where it will leave a greasy film on the base of the windshield

• Since the heater core is enclosed inside the heater box you wont be able to visually inspect it.– Coolant leaks in the heater core normally work

their way down to the bottom of the evaporator case where they will drip out of the evaporator drain tube.

– The evaporator drain tube is close to the bottom of the firewall

– A leaking heater core will usually discharge a mist of coolant out of the defroster vents where it will leave a greasy film on the base of the windshield

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Head gasket leaksHead gasket leaks

• External head gasket leaks are rare but easy to spot.

• Head gaskets when they fail normally leak internally.

• The coolant leaks into the combustion chamber where it is converted to steam in the combustion process.

• External head gasket leaks are rare but easy to spot.

• Head gaskets when they fail normally leak internally.

• The coolant leaks into the combustion chamber where it is converted to steam in the combustion process.

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Head gasket leaksHead gasket leaks

• White smoke from the exhaust is evidence of a relatively large leak.

• Small coolant leaks will produce a distinct exhaust odor.

• Remove the spark plugs and examine them. • If one spark plug is unusually clean and free

of carbon deposits it is evidence of a coolant leak.

• White smoke from the exhaust is evidence of a relatively large leak.

• Small coolant leaks will produce a distinct exhaust odor.

• Remove the spark plugs and examine them. • If one spark plug is unusually clean and free

of carbon deposits it is evidence of a coolant leak.

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Finding leaks with ultraviolet lightFinding leaks with ultraviolet light

• Small coolant leaks can sometimes be difficult to pinpoint.

• Dye can be added to the coolant that glows when illuminated with an ultraviolet light source.

• Special UV absorbing glasses are required when using a UV light.

• Small coolant leaks can sometimes be difficult to pinpoint.

• Dye can be added to the coolant that glows when illuminated with an ultraviolet light source.

• Special UV absorbing glasses are required when using a UV light.

• Never look directly at the UV light – even when wearing UV glasses.

• Never look directly at the UV light – even when wearing UV glasses.

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Bleeding the heater coreBleeding the heater core

• When air gets into the cooling system during repair or servicing the cooling system may need to be burped to purge the air trapped in the heater core.

• Some cooling systems have a bleeder screw on the heater outlet hose or one the high point on the engine where air from the core will collect.

• The system is lightly pressurized. Open the bleeder and allow coolant to leak out until a steady stream with no bubbles is observed.

• When air gets into the cooling system during repair or servicing the cooling system may need to be burped to purge the air trapped in the heater core.

• Some cooling systems have a bleeder screw on the heater outlet hose or one the high point on the engine where air from the core will collect.

• The system is lightly pressurized. Open the bleeder and allow coolant to leak out until a steady stream with no bubbles is observed.

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Burping the cooling systemBurping the cooling system

• If there is no bleeder screw there is sometimes a temperature sensor that can be loosened.

• When all else fails you can loosen the heater hose where it connects to the core and pry the hose away from the tube with a hose removal tool.

• In some vehicles you may have to jack the front of the car up a foot or more with a floor jack to allow the air in the system to return to the expansion tank or radiator core.

• If there is no bleeder screw there is sometimes a temperature sensor that can be loosened.

• When all else fails you can loosen the heater hose where it connects to the core and pry the hose away from the tube with a hose removal tool.

• In some vehicles you may have to jack the front of the car up a foot or more with a floor jack to allow the air in the system to return to the expansion tank or radiator core.

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Determining if there is air in the systemDetermining if there is air in the system

• You can generally tell if there is air still in the system by counting the number of strokes of the pressure tester needed to pressurize the system a few psi.

• If it takes more than three strokes of the pump to get the needle to move there is still some air in the system.

• You can generally tell if there is air still in the system by counting the number of strokes of the pressure tester needed to pressurize the system a few psi.

• If it takes more than three strokes of the pump to get the needle to move there is still some air in the system.

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Low engine temperatureLow engine temperature

• Overcooling or low engine temperature is caused by a stuck open, incorrect or missing thermostat.

• The OBDII system monitors the operation of the cooling system and will set a code if the engine coolant temperature does not rise to within 20 degrees of thermostat opening temperature after 12 minutes of driving above 15 mph.

• The check engine light will illuminate and a P0125 code will be set.

• Overcooling or low engine temperature is caused by a stuck open, incorrect or missing thermostat.

• The OBDII system monitors the operation of the cooling system and will set a code if the engine coolant temperature does not rise to within 20 degrees of thermostat opening temperature after 12 minutes of driving above 15 mph.

• The check engine light will illuminate and a P0125 code will be set.

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Digital pyrometerDigital pyrometer

• A digital pyrometer displays the surface temperature of objects by the measuring the intensity of infrared light produced by the object.

• The object to be measured cannot have a shiny or highly reflective surface.

• A laser pointer is used with most infrared pyrometers. The laser beam is used to aim the sensor and has no bearing on the measurement.

• A digital pyrometer displays the surface temperature of objects by the measuring the intensity of infrared light produced by the object.

• The object to be measured cannot have a shiny or highly reflective surface.

• A laser pointer is used with most infrared pyrometers. The laser beam is used to aim the sensor and has no bearing on the measurement.

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Determining if the engine is at normal temperatureDetermining if the engine is at normal temperature

• The temperature of the coolant outlet – where the upper radiator hose connects to the engine – should be within 20 deg of the thermostat rating.

• The temperature of the heater supply hose should also be within 20 degrees of t-stat temperature.

• With the fan on high speed and the temperature at maximum there should be a 40 degree or larger drop in temperature between the heater inlet hose and outlet.

• The temperature of the coolant outlet – where the upper radiator hose connects to the engine – should be within 20 deg of the thermostat rating.

• The temperature of the heater supply hose should also be within 20 degrees of t-stat temperature.

• With the fan on high speed and the temperature at maximum there should be a 40 degree or larger drop in temperature between the heater inlet hose and outlet.

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Incorrect type thermostat Incorrect type thermostat

• If a bypass valve type thermostat is replaced with a conventional type thermostat the system will overcool.

• The bypass valve closes the bypass passage when the t-stat opens.

• If a bypass valve type thermostat is replaced with a conventional type thermostat the system will overcool.

• The bypass valve closes the bypass passage when the t-stat opens.

T-stat with bypass valve Conventional T-stat

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Insufficient heat – engine temp normalInsufficient heat – engine temp normal

• Possible causes:– Restricted heater core– Faulty heater shutoff/control valve– Faulty blend door actuator

• Possible causes:– Restricted heater core– Faulty heater shutoff/control valve– Faulty blend door actuator

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Restricted heater core testRestricted heater core test

• The classic test for heater core and heater valve testing is to disconnect the heater hoses an run water from a garden hose through the core.

• Use a section of universal heater hose and a funnel.

• Do not connect the heater core directly to the garden hose or use shop air pressure to test for flow. It’s possible to blow the side tanks off with that kind of pressure.

• The classic test for heater core and heater valve testing is to disconnect the heater hoses an run water from a garden hose through the core.

• Use a section of universal heater hose and a funnel.

• Do not connect the heater core directly to the garden hose or use shop air pressure to test for flow. It’s possible to blow the side tanks off with that kind of pressure.

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Damaged heater core tubesDamaged heater core tubes

• The inlet tube shown here has been partially crushed during heater hose service.

• The inlet tube shown here has been partially crushed during heater hose service.

Pinched tube

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Damaged heater core tubesDamaged heater core tubes

• The aluminum heater core tubes is extremely soft and can be easily damaged when the heater hoses are replaced by twisting the hose ends off with pliers.

• If the hose is being replaced slice the hose lengthwise with a razor blade then peal the hose away.

• The aluminum heater core tubes is extremely soft and can be easily damaged when the heater hoses are replaced by twisting the hose ends off with pliers.

• If the hose is being replaced slice the hose lengthwise with a razor blade then peal the hose away.

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Blend door actuator testingBlend door actuator testing

• Cable type blend door operation can normally by visually confirmed. Some trim panels may need to be removed.

• Electric blend door actuators may be visible but you usually can’t confirm there operation unless you can observe the movement of the door itself.

• It may be possible to insert a bore scope through one of the floor vents to observe the operation of the door.

• Cable type blend door operation can normally by visually confirmed. Some trim panels may need to be removed.

• Electric blend door actuators may be visible but you usually can’t confirm there operation unless you can observe the movement of the door itself.

• It may be possible to insert a bore scope through one of the floor vents to observe the operation of the door.

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Too much heatToo much heat

• Occasionally the complaint is that the heat won’t turn off – the windows need to be rolled down even in the winter to be comfortable.

• In nearly all cases the cause is a blend door stuck in the hot position.

• Often there is something physically obstructing the door from moving.

• Rodents often find a way into the HVAC system and build nests. It’s not uncommon to find acorns and other objects inside the heater box.

• Occasionally the complaint is that the heat won’t turn off – the windows need to be rolled down even in the winter to be comfortable.

• In nearly all cases the cause is a blend door stuck in the hot position.

• Often there is something physically obstructing the door from moving.

• Rodents often find a way into the HVAC system and build nests. It’s not uncommon to find acorns and other objects inside the heater box.

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Mode control failuresMode control failures

• In vehicles with vacuum operated mode doors a system that has only the defrost mode operating no mater what position the control is set to is likely to have a vacuum leak between the intake manifold and the mode control valve.

• If no air is coming out of the face level vents but the other two modes work well the vacuum leak may be between the control valve and the actuator or the actuator may be faulty.

• Vacuum operated mode doors can be easily tested with a hand operated vacuum pump.

• In vehicles with vacuum operated mode doors a system that has only the defrost mode operating no mater what position the control is set to is likely to have a vacuum leak between the intake manifold and the mode control valve.

• If no air is coming out of the face level vents but the other two modes work well the vacuum leak may be between the control valve and the actuator or the actuator may be faulty.

• Vacuum operated mode doors can be easily tested with a hand operated vacuum pump.

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Recirculation mode testingRecirculation mode testing

• The recirculating mode door operation is difficult to test because it operates on the inlet side of the system.

• A smoke machine is a good method of determining if the recirculation door is functioning

• The recirculating mode door operation is difficult to test because it operates on the inlet side of the system.

• A smoke machine is a good method of determining if the recirculation door is functioning

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Blower motor – not operating at any speedBlower motor – not operating at any speed

• Check the blower motor fuse[s]• Check for voltage between the two

terminals on the blower motor harness connector

• On older cars with a single wire connector check that the motor housing is grounded to the body.– Connect a test light to Battery + terminal and

touch the fan housing with the test light probe – it should illuminate if the ground connection is good.

• Check the blower motor fuse[s]• Check for voltage between the two

terminals on the blower motor harness connector

• On older cars with a single wire connector check that the motor housing is grounded to the body.– Connect a test light to Battery + terminal and

touch the fan housing with the test light probe – it should illuminate if the ground connection is good.

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Blower motor – not operating on low or medBlower motor – not operating on low or med

• Remove the blower resistor and check resistance between terminals.

• There should be less than 10 ohms resistance between any two terminals.

• If the resistor checks out OK the fault may be in the blower motor switch.– AllData should have a ‘truth chart’ that identifies

which terminals on the switch have continuity at each switch position

• Remove the blower resistor and check resistance between terminals.

• There should be less than 10 ohms resistance between any two terminals.

• If the resistor checks out OK the fault may be in the blower motor switch.– AllData should have a ‘truth chart’ that identifies

which terminals on the switch have continuity at each switch position

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Electronically controlled HVAC diagnosisElectronically controlled HVAC diagnosis

• A scan tool is normally used at a dealership to diagnose electronically controlled heating and A/C components.

• The scan tool can display the position of the door or speed of the fan commanded by the control head.

• The scan tool can also send a signal to the BCM to operated a door or turn on the fan.

• Most electronic HVAC systems monitor their operation and set failure codes if a fault in the system is detected.

• A scan tool is normally used at a dealership to diagnose electronically controlled heating and A/C components.

• The scan tool can display the position of the door or speed of the fan commanded by the control head.

• The scan tool can also send a signal to the BCM to operated a door or turn on the fan.

• Most electronic HVAC systems monitor their operation and set failure codes if a fault in the system is detected.

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Fan noiseFan noise

• Possible causes– Leaves and twigs trapped between the fan and

fan housing• Rattling type noise

– Fan motor bearing failure• Howling or screeching type noise• Often a failed bearing only makes noise when cold or

for a few seconds after the fan is turned on

• Possible causes– Leaves and twigs trapped between the fan and

fan housing• Rattling type noise

– Fan motor bearing failure• Howling or screeching type noise• Often a failed bearing only makes noise when cold or

for a few seconds after the fan is turned on

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OdorOdor

• Common sources of HVAC odor:– Rodent nests in HVAC plenum or heater box– Mold on A/C evaporator core– Evaporator leaks– Heater core leaks

• Common sources of HVAC odor:– Rodent nests in HVAC plenum or heater box– Mold on A/C evaporator core– Evaporator leaks– Heater core leaks

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Rodent nests and mold removalRodent nests and mold removal

• Cleanup of rodent nests normally requires removal and disassembly of the heater box so that it can be cleaned and disinfected.

• Mold on the evaporator or heater core can be treated with chemicals that can be sprayed into the heater box with out removing it from the vehicle. This procedure will only partially clean the evaporator.

• The best method of removing mold from the evaporator and heater box is a complete disassembly of the box so that the evaporator can be immersed in the disinfecting chemicals.

• Cleanup of rodent nests normally requires removal and disassembly of the heater box so that it can be cleaned and disinfected.

• Mold on the evaporator or heater core can be treated with chemicals that can be sprayed into the heater box with out removing it from the vehicle. This procedure will only partially clean the evaporator.

• The best method of removing mold from the evaporator and heater box is a complete disassembly of the box so that the evaporator can be immersed in the disinfecting chemicals.