Heater only blowing cold air.

Heater blower works fine, but the heater only blows cold air.
Experienced mechanics share their insights in answering this question :
There are two likely causes for your concern. Either your heater core inside your dashboard is clogged, or one of the doors that directs the air to your heater core is malfunctioning. I would enlist the help of a certified mechanic to check your heater for these concerns and have him make the necessary repairs to get your heater blowing hot air again.

How to Identify and Fix Common car Problems ?

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Cold Air Blowing Instead of Heat

Below are some common explanations as to why your heater is not working in your Mercedes-Benz: Antifreeze/Coolant Leak in Radiator or Heater Core. Defective Thermostat. Faulty Heater Fan.

Mercedes-Benz is recalling 4227 A-Class models from model years 2018 to 2019 due to condensation potentially interfering with systems. Mercedes-Benz is recalling 2018-19 A-Class models due to an incorrectly-installed part in the air-conditioning system.
Low refrigerant pressure can cause the left side to blow warmer air than the right side, but in no case will low pressure cause the air on one side to be warmer than the outside air. Your problem is that the left side heater is stuck on.
A car A/C blowing hot air is often the result of a refrigerant leak. Refrigerant is a liquid that circulates through your car`s A/C system, expanding and contracting as it removes heat and humidity from the cabin. None of the other A/C components will function correctly without proper refrigerant levels.
If your coolant level is a-okay, but your car heater is blowing cold air and your engine is overheating, then you have a clog in your cooling system. Conversely, if your engine temperatures are unrealistically low after a drive, your thermostat is likely the culprit.
If your furnace is blowing cold air in your home, this is a sign of an issue with the flame detector, gas supply, air filter, pilot light, or condensate lines. Many of these issues are able to be easily solved on your own by sanitizing or replacing components in the gas furnace.
Common signs include inconsistent cooling, out-of-date software, and uneven air distribution, since the module controls the whole AC system.
A failed thermostat will have your temperature gauge reading high on the dashboard. When you start your vehicle if the gauge shows in red within 15 minutes, this indicates a problem with the thermostat. An erratically changing temperature gauge is another warning sign of a failing or failed thermostat.
Blend door actuators are the most common reason for the car air conditioning to blow cold air on one side and hot air on the other. They can be diagnosed with an advanced scan tool. The scan tool can tell if the blend door actuator should be in a different position than commanded.
Common Causes of an Air Conditioner Blowing Warm or Hot Air

These can be due to clogging issues, electrical problems, low refrigerant, evaporator coil malfunctions, or compression problems. If you`ve ever had the ac system in your car stop functioning, it`s often due to a refrigerant leak or dirty coil.

Faulty heater cores and low or contaminated coolant levels often come hand in hand, and both issues may lead to your engine overheating and your heater not blowing hot air.
One of the most common reasons your car AC is blowing hot air is because of a refrigerant issue—specifically, a loss of refrigerant. This loss of refrigerant can occur either due to a leak or because your car`s refrigerant levels are too low.
The lukewarm air appearing in your heater can be the outcome of a leaky duct. If your air ducts are leaking, cool outside air is making its way into your ductwork. This can cause the air to really feel only lukewarm. The repair: Duct sealing.
The ambient temperature sensor (switch) is located either behind the front grille or in the front bumper. Its only job is to monitor air temperature (which it does through increasing/decreasing resistance in response to temperature fluctuations).
Most of the time it is close to the thermostat of the cooling system, or in some cases even inside of it. Note: Some engines may actually have a pair of sensors—one sending information from the engine to the control unit, the other sending information from the control unit to the dash.
The AC/heater control module is a computer inside your car that controls and regulates the operation of your car`s HVAC system. Occasionally, the module might fail and will likely produce a fault code.
Start your car`s engine and allow it to idle. Look through the radiator filler neck to see if the coolant flows. At this time, it should not be flowing as your car has not reached the operating temperature to cause the thermostat to open. If you find the coolant is flowing, it means the thermostat valve is open.
Common Car Heater Problems

The heater switching system might be faulty. The cabin air filter might be choked, restricting the airflow through the heater core. The thermostat valve might not be working right. The heater core might be clogged.

Common Car Heater Problems

The heater switching system might be faulty. The cabin air filter might be choked, restricting the airflow through the heater core. The thermostat valve might not be working right. The heater core might be clogged.

Here are the most common reasons why your car heater isn`t blowing hot air. Low coolant: Whether caused by a leak or water evaporation, low coolant is the most common source of poor heater output. Thermostat: A stuck-open thermostat prevents the engine (and coolant) from heating up.
If just one (or a few) of your radiators aren`t heating up, the most common reason for this is trapped air. If you`ve just turned the heating back on after the summer, air can become trapped in your radiators, causing them to be warm at the bottom but cold at the top.
Here are the most common reasons why your car heater isn`t blowing hot air. Low coolant: Whether caused by a leak or water evaporation, low coolant is the most common source of poor heater output. Thermostat: A stuck-open thermostat prevents the engine (and coolant) from heating up.
If the heating system isn`t working at all (no hot or cold air is being blown into the car), this is likely due to a faulty blower motor or an issue stopping power from reaching the blower motor, but that`s not the only possible reason. In general, car heater issues can be caused by the following: Low antifreeze.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

My heater is blowing air through the driver side air vents but is blowing cold air through the passenger side and rear console ven
ANSWER : Hi there:

Climate controlled vehicles have multiple electrical relays that open and close vents to maintain the desired temperature. In some instances, these relays can wear out overtime. However, it’s also common for debris to clog up vents (especially side vents) which may restrict the flow of cool air. The best way to determine why your AC is not working efficiently, it might be best to have a professional mechanic complete a AC inspection; so they can pinpoint the source of your issues and recommend the right repairs.

Read Full Q/A … : Heater only blowing cold air.

Air conditioning blowing mildly cold air on the coldest setting, turned off/on again, now blowing cold air, should it be checked?
ANSWER : If you are getting ready for a long trip and suspect the cooling fan may be not coming on for the radiator and a/c then you should have the a/c and cooling system performanced checked before trip. Nothing worse than breaking down when out of town in a strange area.

Read Full Q/A … : Heater only blowing cold air.

My car heater will blow hot air and drive fine for 30 minutes then my heater blows cold air and my car overheats
ANSWER : Hello. With the recent repairs that have been made to the vehicle, there is only one main heating component that you have not looked into. This would be your heater core. The heater core is responsible for pulling hot coolant from the engine. This hot coolant runs through the heater core as the ambient air is pushed through to warm before entering the cabin. If the coolant can’t flow through the heater core, then the air will blow cold. This can be caused by a clog, a faulty switch, or a process known as electrolysis (electrical current running through coolant). Unless there is a clog that can be dislodged, these issues will all result in a new heater core. To get a precise diagnosis of the problem, I recommend having an expert inspect the overheating problem so this can be resolved.

Read Full Q/A … : Heater only blowing cold air.

everytime I turn my car on the ac starts to blow air even if I switch it off. it won’t blow cold air or heat.
ANSWER : Hi there. Based on your question and input, it looks like your AC control switches are damaged, causing the vents to activate even if the switch is not activated. This is sometimes an electrical problem, as it could be triggered by a damaged electrical relay. You might want to have a professional mechanic complete an AC is not working inspection, so they can determine what is causing this issue you’re experiencing and recommend the right repair.

Read Full Q/A … : Heater only blowing cold air.

Hot air mixed with cold blows from air conditioning
ANSWER : Hey there. You will most likely have to have a mechanic bypass the heater coolant lines to have this resolved. Your A/C may not be controlling the air flow inside the evaporator correctly out of the vents and may be the blend door actuator stuck in the heat position. Have the AC system diagnosed first before bypassing the heater.

Read Full Q/A … : Heater only blowing cold air.

My car is overheating and my heater is blowing cold air on and off
ANSWER : The heater not working in some cases may be related to the overheating problem you are also having. This may be due to a faulty heater blower motor or potentially a bad heater core. As you may know, the heater core is a small radiator like unit that circulates the hot coolant from the engine through the heater core which then uses this warm coolant to heat the inside of the car with the help of the blower motor that blows the warm air through the vents inside the car. When the cooling system is not properly circulating coolant through the motor, this results in the warm coolant not being pumped through the heater core properly in order to warm the inside of the vehicle.

Engine overheating can be caused by a number of things such as low coolant levels, a faulty thermostat, or a failing coolant fan switch. As you may know the coolant fan switch helps to maintain the proper coolant temperature by turning on and off at specific temperature thresholds. When this switch is not working properly, this can cause the fans to come on intermittently, all the time or sometimes not at all. When this happens you will notice a temperature spike and drop occasionally as the fan comes on and off. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. As mentioned above, this also restricts the warm coolant from flowing through the heater core which uses this to blow warm air into the cab of the vehicle. I would suggest having an expert from Your Mechanic come to your home to diagnose your cooling system.

Read Full Q/A … : Heater only blowing cold air.

My air is blowing cold-hot-cold-hot-cold-hot…
ANSWER : It is possible that you have a leak in the AC system. There are pressure switches that will turn off the compressor if the pressure is too high or too low. The low refrigerant level could cause the AC compressor to cycle on and off. If you would like to have this done, a certified technician from YourMechanic can come to your car’s location to diagnose the AC system and make the correct repair.

Read Full Q/A … : Heater only blowing cold air.

While driving defroster set to hot blows hot air as it should, while idling it is blowing cold air.
ANSWER : First, the coolant level should be checked to make sure the radiator is full. While the overflow tank may be full, the radiator cap must be taken off to check the level inside the radiator. If you find the level is very low, you have a coolant leak that must be fixed. If coolant levels are normal, an engine thermostat or heater control problem may be what you’re experiencing. Consider hiring an experienced technician like one from YourMechanic who can come out and take a closer look at your lack of heat concern to offer a more personal diagnosis.

Read Full Q/A … : Heater only blowing cold air.