How to troubleshoot car heater air conditioner problem

Cold/hot air flow only in my car ! What happened ?

In winter season or some of cold day, hot air is anticipated to make us being warm. But there is only cold air coming out from heater. It is really crazy situation.

Engine temperature indicator on dashboard is normal. That means engine is now hot to provide heating.

If we visit car care center nearby, then this problem could be fixed out by repair man. But we should repair by myself if we drive some distant rural area or at night time.

If there is only cold/hot air from heater/air conditioner, what should we check ? Could it be fixed by myself ?

 

Let's understand the operation of car heater !

How does car heater provide hot air flow ? Is there any electrical wire to get heating like electric heater ? It's not. Car heater uses engine's hot coolant.

If car heater is not working properly, then there should be coolant circulation issues.

Basic operation or schematic of car heater, sometimes called as HVAC(Heating, Ventilation and Air Conditioning) is as follows.

Even we are talking about the heater, there is also air conditioner inside of engine room to provide cold air flow in summer season. Cooling and heating is correlated since those are switched by temperature control.

Starting point is just engine. If engine is run with gasoline or diesel combustion, then heat is generated from engine. This is being cooled by coolant surrounded engine.

At the initial time of engine startup, coolant temperature is so low. If engine coolant is circulated at the initial time when engine is still cold, engine heating will be slowed.

Therefore there is one valve called Thermostat to stop coolant circulation at an engine startup time. 

Thermostat is just installed inside of coolant pipe. Thermostat is blocking engine coolant flow until certain level of temperature is reached. If temperature is warm reasonably, then thermostat open itself so that coolant is flowed freely.

Hot coolant is flowed into car cabin room so that it can be used for heating there. If wind is getting through over this coolant pipe, hot air can be come out.

But car requires both heating and cooling. Therefore air conditioner's cold pipe is also come into the cabin room near heater. Car should switch between heating and cooling by driver's temperature setting.

The above is what car temperature conditioning system, HVAC is working. Then now we could troubleshoot car heater problem.

 

Insufficient coolant makes heater problem.

As explained in the above operation theory, thermostat blocks coolant flowing per its temperature setting. If thermostat is not working properly, then coolant is not flowed even temperature is already going up to the designated value.

Thermostat can be corroded, contaminated or cracked by aging. These makes Thermostat being blocked or stuck in certain position.

 Thermostat, source: wikipedia.org

Normally thermostat is located just near of engine. Please touch and feel a temperature of coolant pipe after engine is warmed up enough. Check also two coolant pipes to cabin room from engine room.

If some coolant pipe is cold while others is warm, then thermostat is not working. This blocks coolant flowing by its aging.

Then we should replace troubled thermostat.

 

Stuck Temp actuator makes heater problem, too.

There is enough engine coolant. Tempstat is also working well. Then we should check temp. actuator(temperature actuator).

Temp. actuator is located at the inside of cabin room. This just switchs between heater and air conditioner.
 

Temperature actuator

Air flow by fan should get through heater at high temperature setting, air conditioner at low temperature setting.

If troubled temp. actuator is stuck at air conditioner side, then there is only cold air flow into cabin room. If it is stuck at heater side, there is only warm/hot air flow into cabin room. These are applicable in all seasons.

Temperature actuator can be easily broken by aging. Last part we should check against heater or air conditioner problem is just temp actuator.

According to component shop, temp. actuator is one of frequently bought components.

Temp. actuator's working video can be watched as following.

Procedure to check car heater/air conditioner problem !

1. Check engine coolant level. If it is insufficient, please supply it enough.

2. If one of coolant pipes into cabin room is cold while the other is warm/hot, then thermostat is troubled. Please replace thermostat near engine.

3. Temp. actuator makes trouble having onlyhot or cold air flowing. Please replace temp. actuator which is located just under of car conditioning control panel.

Above explanation or check list could be helpful to troubleshoot your car conditioning system.

Good day of you.