By P Sanchez
Last time we took a little stroll back in time and saw how driver and passengers deal with the cold in their private vehicles during the decade following the 1900s which were the formative decades of the automobile. For this article, we’re checking the parts that make the modern automobile heating system and know a few of its troubleshooting techniques.
The cabin heating system of an automobile is simpler compared to the air-conditioning system. It’s just like a smaller version of the engine’s cooling system. First to know is the coolant which is the fluid medium that absorbs and releases heat. It could be anything from old school distilled water to the more advisable water-glycol formula known as antifreeze.
The later offers several advantages over water. One is that coolant has a higher boiling point which reduces the chance of a boilover. A boilover is when the coolant turns to vapor or steam because of extremely high engine temperature. Hot vapor can cause high internal pressure hoses and tubes to burst, and even cause the engine block to crack. Vapor is also a poor heat conductor which means parts of the engine loses protection from heat and will eventually mechanically fail.
Another advantage of coolant is its lower freezing point compared to water (hence the antifreeze name). Physics 101 shows us that ice occupies a larger volume than liquid water, which means water freezing in the engine is detrimental. Solid ice can lock up the engine from starting and it can even split the engine block. Ironically, ice can also cause overheating because ice can block tubes and passages, preventing coolant circulation and heat dissipation. Ice can also block hot coolant from bringing heat into the cabin.
Pump and Parts
Let’s start with the water pump, the heart of the engine cooling/cabin heating system. The water pump circulates the coolant in and out of the engine. The cooled coolant is pumped into the engine where it absorbs excess heat from the engine and allows the engine to run at an optimal temperature. Most of the heated coolant exits the engine through a major tube that leads to the front radiator where the excess heat is released into the atmosphere and for the cooling cycle to repeat anew.
But some of the hot coolant is carried off by a smaller diameter tube to the cabin. The flow of hot coolant entering the cabin is regulated by a valve that’s electronically controlled in conjunction with a thermostat in the cabin. After which, the hot coolant enters a heater core located in the cabin airbox which is also shared by the A/C evaporator. Cold cabin air is forced through the heater core by a centrifugal fan. Heat is then exchanged and comforting warm air is vented into the cabin. The cooled coolant is drawn out the heater core through pressure difference and carried through tubes back to the engine to begin the cycle anew.
As shown, a car’s heating system is not entirely complicated, therefore troubleshooting is easier compared to the other car system.
Airflow issues: whether it’s A/C cooling or heating you’re after, once air is not flowing out of your vents, it means that there’s an issue with the centrifugal fan. To be doubly sure, turn on the heater and max out the fan switch. If air is not flowing out, put your hand over the vent. If you feel hot air rising from the vent, you know that the core is intact and heating up, but the fan’s motor is probably fried and cabin air is not blown through the heater core.
You can also try checking air flow with the A/C rather than heating. If switching to A/C introduces airflow then there might be an issue with the plastic flap that controls the blend of air between the heater core and the A/C evaporator. See also if there’s airflow directed to your feet or up the windshield. If there is, then another plastic flap in the airbox that functions to redirect the heated or cooled air to different parts of the cabin is at fault.
Air is blowing but it is cold. This means the heater core is not getting the hot fluid it needs. There are several reasons that could cause this. First, check your coolant levels. If there’s not enough to go around then your heater core is probably starved of hot coolant. Check the coolant reservoir levels and make sure it’s between min and max. Simply add more coolant if needed.
If it’s particularly cold weather, consider the possibility that your coolant may have frozen, preventing cooling circulation. How likely your coolant freezes depends on your coolant mix. A standard 50/50 antifreeze-water mix will have a 5-degree Fahrenheit ( negative 15-degree Celcius) freezing point. A lesser proportion of antifreeze will raise the freezing point and make coolant freezing in cold weather likelier. Turn off the engine and allow the latent heat to thaw the coolant before retrying.
If coolant levels are good and you’re using a good proportion of antifreeze in your system (with at least 50% antifreeze, or more) then the coolant might not be circulating. Run the engine, if the engine temp on the dash starts creeping pass mid-hot and the cabin is still not getting hot airflow, it means the water pump has gone bad. But if the engine is not overheating then something is probably preventing the hot coolant from entering the heater core and it’s probably a bad heater valve or an issue with the electronics that are keeping the valve closed. Replacing a water pump, heater valve or repairing climate control electronics are undertakings best left to car repair specialists.