Why The Heater In Your Truck Is Blowing Cold Air

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You go to get into your truck and start it up. Once started, you go to turn the heat on and realize your truck’s heat is blowing cold air. You ask yourself, ‘why is my truck heater blowing cold air?’

Your truck blowing cold air could be because of a bad heater core, a bad blower motor, a bad thermostat, or low coolant. Any one of these things can cause your truck to blow cold air out of the vents in your vehicle’s cabin. 

I’ve been diagnosing heater issues in the winter for five years, and I’ve found cold air when you want hot, always comes down to one of the issues mentioned above.

For more information about how these items work and to find out which one is affecting your vehicle, continue reading. 

Table of Contents

What Is A Heater Core?

truck heater blowing cold air 2 Why The Heater In Your Truck Is Blowing Cold Air

A heater core is like a small radiator that’s placed inside your vehicle’s dashboard. In total, a heater core is a series of small tubes with metal fins placed around them. 

The way a heater core works is that when coolant from your vehicle’s engine is warmed up by engine combustion, coolant is routed to the heater core inside your dashboard. 

Once the coolant starts flowing through your heater core a blower motor inside the dashboard takes the heat from the heater core, and blows it inside your vehicle’s cabin. 

A heater core is a simple gadget but very effective at its job since it can heat your whole vehicle with just one little series of tubes. But this is also why it takes time for your car to warm up inside. 

The coolant has to get warm enough to make a noticeable difference before it’s routed to your heater core, so the engine shuts off flow to the core until that time.

How Heater Cores Can Fail

There are a couple of things that can go wrong with a heater core as well. The first thing is that the core since it’s really just one long tube bent into a series, can get clogged with debris. 

Leaves can get into your coolant reservoir and clog the heater core over time. As well, mice that like to build nests can start dropping things into the reservoir which can clog flow through the whole system and clog the heater core. 

A leak from your heater core can also cause no heat, as well as other serious mechanical issues such as overheating. Leaks can spring from lines that connect the heater core to your engine block. 

A leak from a heater core can cause low or no warmth provided by the engine. Lastly, the heater core can just start to lose its heat-transferring capabilities from wear and need to be replaced. 

Note that replacing a heater core is one of the most intricate jobs a mechanic can do, so do so with extreme caution. 

What Is A Blower Motor?

A blower motor is a small motor that resides in your dashboard, usually under your glove compartment. It’s a big fan that blows air over either your AC evaporator, or your heater core. 

The blower motor looks like a merry go round that spins very fast and quietly. Your blower motor in your vehicle is responsible for filling the whole cabin with hot or cold air so you can be sure it’s a powerful little device. 

How Blower Motors Can Fail

truck heater blowing cold air Why The Heater In Your Truck Is Blowing Cold Air

The blower motor is connected to a duct system in your vehicle that may or may not be electrically controlled.

If your car is made after around 2005, it’s most likely a electronically controlled duct system meaning the ducts change the flow of air by closing and opening different vents electronically. 

What this means for your truck that’s blowing cold air is that while the blower motor is still working (blowing cold air), your vents could be failing. 

Your electronic vents could be stuck to the path that allows only air from your AC to blow, instead of your heater core. This faulty vent will cause your vehicle to blow cold air. 

Another reason your car could be blowing cold air is because the blower motor usually works on a resistor circuit, meaning that it allows the same voltage through different paths. 

And each path allows more or less voltage through allowing the fan to spin faster or slower. If the circuit has become damaged, your blower motor could become stuck on the lowest speed, making it feel like cold air is coming out of your vents.

What Is A Coolant Thermostat?

A coolant thermostat is a device that regulates the engine’s temperature. Because the engine has combustion inside the cylinders, the engine block and its internals start to get very hot. 

To mitigate this heat, coolant (basically water) is rushed around the engine block. Once the engine gets hot enough, the coolant thermostat opens up, and allows the water that was sitting inside the engine block to be exposed to atmospheric temperature. 

With some added fans and a radiator, the engine coolant’s temperature is lowered. Once lowered, the coolant is circulated back into the engine block where it starts to cool down the engine. 

How Can A Thermostat Cause Cold Air To Blow?

A thermostat is usually built using a was pellet that expands and contracts with heat. When the pellet heats up, the thermostat opens, and allows coolant to be circulated to other parts of the engine. 

When the thermostat is closed, coolant stays in the engine block and doesn’t flow anywhere else. Well, if the thermostat breaks, coolant would not be circulated to your heater core. 

Nothing would be flowing through your heater core and you would not feel any heat coming from your truck’s vents. 

Basically, your heater core would be getting blocked from receiving any warm coolant, and therefore, your blower motor would just be blowing around air that’s the same temperature as it is outside. 

A thermostat can be relatively easy to fix depending on your truck’s model, so do some research beforehand. But it’s usually two bolts and a clamp that hold it all together so you can most likely do this yourself and at home. 

Low Coolant

Low coolant can cause your truck to blow cold air through the vents. When coolant is low in your vehicle,there’s not enough antifreeze to reach your heater core. If there’s not enough coolant to circulate through the system, there’s no coolant that can be pushed to the heater core. 

Therefore, if there’s no warm coolant running through your heater core, the only thing your blower motor will be pushing around is cold air. 

Key Takeaways

truck heater blowing cold air 1 1 Why The Heater In Your Truck Is Blowing Cold Air
  • Your truck is blowing cold air because of one of the following reasons: A bad heater core, a bad blower motor, a bad thermostat, or low coolant.
  • A heater core can become clogged or damaged causing your truck to blow cold air.
  • A blower motor can cause vents to stick, causing only the A/C vents to turn on.
  • A thermostat can fail, causing a heater core to receive no coolant.
  • Low coolant can cause your truck to blow cold air.