Please Select Username to appear on public areas of the site like community and recipe comments. (c) 2012-2016 EricTheCarGuy, All Rights Reserved.DIY, How To Auto Repair Heater hose clamps like pictured can be removed easily with special hose clamp tools.  In this auto service repair article, we cover how car heaters work. Knowing how the automotive heater system is designed to work, allows the car owner or auto tech to diagnose problems more quickly and easily. Car heaters are designed much differently than home heaters, therefore diagnosing and repairing auto heaters requires different service procedures. Auto service tips and information provided in this car repair article is written by a master automotive technician that has many years in the field. is provided in simple language that is easy to understand by anyone – experienced in auto service or not. (Be sure to read the questions and answers in the comment section at the end of the article. Also see  for even more tips.)

It’s always best to have a basic understanding on how a particular system works, to be able to diagnose problems easier. When a car heater blows cold air, there are several possibilities that should be considered. Read on to learn more. Many people are unaware that there’s NOT an electric element in a car’s heater system. Heater elements are common in portable heaters used in the home – however automobiles use coolant from the car engine’s cooling system to transfer heat to the passenger compartment, through the use of a heater core. what ac unit for house sizeThat’s why a car heater doesn’t start blowing warm air until the vehicle reaches operating temperature. ac unit line setThe heater core looks similar to a small radiator – it has coils and fins to transfer heat to the air.  how much does central ac unit cost

The car engine’s coolant is pumped through the heater core while the fan (also called a blower), pushes air through the heater core fins. When air blows through the heater core fins the air is warmed and in turn heats up the passenger compartment. One of the most common causes of a car heater blowing cold air is from low coolant.  As stated before, coolant is what warms the heater core – if the coolant is low, there may not be enough heat transfer from the heater core to the air to heat the passenger compartment. When it ‘s cold outside, low coolant may not cause the engine to overheat right away. If it did cause the engine’s temperature gauge to read hot, the driver would be warned and the  low coolant problem would be discovered more quickly. The point is, when checking the heater be sure the radiator is full of coolant. Once the coolant is verified to be full, feel the heater hoses that go to the firewall. With the engine at normal operating temperature, BOTH of the heater hoses should be hot to the touch.

If only one is hot, this indicates there is a blockage in the heater core or there is air trapped in the heater core preventing proper flow. Using a Lisle coolant funnel is the best way to remove air from a car’s cooling system. If the coolant is really brown, has been neglected, or if stop leak has been used at some time in the car’s service history, the heater core could be stopped up. The blockage can sometimes be cleared  by removing the heater hoses and using a garden hose with a sprayer to flush the heater core out. If neither of the hoses are hot to the touch, there could also be a malfunctioning heater control valve, if used on the model you’re working on. Check for presence of a heater control valve by following the heater hoses back to the engine. Sometimes, a vacuum line could have a break causing there to be no vacuum to operate the valve. Also it should be noted that if this is your first winter with this car (and you’re unfamiliar with the car’s repair history), the previous owner could have by-passed the heater core due to a leak.

When a heater core leaks, the passenger side carpet will become soaked with coolant. This should not be confused with an AC (condensation) water leak. The labor involved to change a heater core is usually several hours depending on the model. This is the reason some people will loop the heater hoses together with a 5/8″ union – by-passing a leaking heater core instead of repairing it properly. After the previous steps are taken to insure the heater core is in the loop, the coolant is full and hot water is circulating in and out of the heater core, read the following regarding the HVAC (Heating, Ventilation & Air Conditioning) case. Doors within the heater case are either controlled by electric actuators, cables or vacuum motors. Adjust the heat control to both extremes while listening for movement of the blend door. With a cable operated heater door it’s easiest to hear the door thump when it closes. If the door is not operating, find the door that controls the airflow across the heater core.

If there is an electric motor that controls the door, tapping on it can sometimes make it work temporarily for testing purposes. A vacuum operated motor needs vacuum to work, so using a hand-held vacuum pump for testing is usually the easiest way to check operation. If the vacuum motor does not hold vacuum, the diaphragm is leaking requiring replacement. To go deeper into diagnosis of the AC control head’s function and diagnosis, specific vehicle  may be needed. Related Car Repair Article and Mechanics Tools – General Automotiove Tools – Cooling System ServiceWhat you will learn from Troubleshooting Broken Thermostats article:One of the most common trouble calls for HVACBasic checks of the thermostat to see if it is broken or?The basics of the thermostatLearn what a heating anticipator is and what type of thermostat uses them.Lots of related useful links to help you learn your HVAC system Troubleshooting Broken Thermostats - The main connection between the air conditioning and heating system and the end user is the thermostat.

Beyond the air conditioning and heating thermostat many people know nothing about their systems that keep them comfortable year round. There comes a time when the thermostat has a problem or the end user wants to replace the thermostat because they think it is a broken thermostat. It is not uncommon for a person to call an HVAC contractor and tell the secretary that they think the thermostat is broken because their air conditioner or heating system does not work.In some instances this is the case while in others the thermostat is not broken but something is wrong with the air conditioning and heating equipment that needs to be repaired. In either case, it is usually best to call an HVAC professional to look at the problem especially if you want to replace the thermostat. There are a few things you can check with your thermostat before you call an HVAC professional. A little thermostat troubleshooting is in order.Related Link: How to Hook up a New Thermostat - A Closer LookTroubleshooting Broken ThermostatsWhat To CheckAn air conditioning and heating thermostat, even if it is a digital thermostat, is simply a temperature switch that turns the air conditioning and heating system on and off.

As with any switch, it needs electricity to function or cause a function with the air conditioning and heating equipment. Most residential and light commercial thermostats are powered by 24 volts A.C. The thermostat gets this 24 volts A.C. from the air conditioning and heating equipment. Usually, this power comes from an air handler in an air conditioning and heating split system and from the main unit for air conditioning and heating package systems. Check the circuit breaker for the air handler to make sure it is not tripped. Also, check the power switch which should be located near the air handling unit. It is not uncommon for people to mistake these switches for a light switch and turn them off. They unknowingly just turned the power off for their air conditioning and heating equipment including their thermostat. That is when they begin to think they have a broken thermostat. If you have a digital thermostat the power display and the thermostat power display light may not function if you have this problem.

Some air conditioning and heating thermostats use batteries to power the backlight which takes us to number two in air conditioning and heating thermostat troubleshooting. Check the power switch and breaker to ensure the power is on before assuming you have a broken thermostatThe back display light for the digital thermostat does not function but the air conditioning and heating system works fine. Check the batteries as some digital thermostats require AA or AAA batteries for the backlight to function on the thermostat.There are two main types of digital thermostats; Digital thermostats that use batteries for the backlight to function and digital thermostats that use the power from the air conditioning and heating equipment. If you don’t know which kind of air conditioning and heating thermostat you have then open the thermostat up and look inside. If you don’t see any batteries or a battery compartment inside the thermostat then your thermostat uses power stealing technology. It is probably an older model digital thermostat and if it is a programmable thermostat then every time you lose power you will lose the program inside which takes us to the next step in air conditioning and heating thermostat troubleshooting.

The programmable thermostat is always losing its program. This is most likely one of the older thermostats that use the power from the air conditioning and heating equipment and every time you lose power you lose the program inside the thermostat. Programming an air conditioning and heating programmable thermostat can be a chore for many people to figure out so a problem like this can be frustrating especially if you live in an area where there are constant power failures. The only solution to this problem is to replace the programmable thermostat with one that uses power stealing technology (it uses power from your air conditioning and heating system to hold the programs) and has a battery back-up just in case you lose power. This can save you lots of trouble and frustration in the long run keeping you from reprogramming the thermostat over and over again when power failures occur.Related Link: How a Programmable Thermostat Works - A Closer Look If the problem is persistent with the thermostat it is important to get back to thermostat basics.

Fix& Broken Thermostats - The BasicsIs the thermostat installed in the proper location? This is very important as a thermostat installed on a wall that has high heat gain or heat loss will never offer you comfort as it will react mostly to the temperature of the wall and not the air in the living space. Additionally, thermostats installed where direct sunlight can hit the thermostat is going to be a problem also. A thermostat located near an outside door or window will be affected every time the door or window is opened or closed. A thermostat should be located close to the return (where the filter is installed) so that it sense and reacts to the air returning to the air handler for conditioning. Additionally, thermostats located near heat sources like hot or cold water pipes, radiant heaters, fireplaces, electrical devices which produce heat, etc… will never offer accurate temperatures and conditioning for the room(s).Is there a big hole behind the thermostat that will feed cool or warm drafts to the back of the thermostat?

All thermostats have a hole behind them where the wires come into the thermostat from the air handling unit. Check this and if you find a big hole behind the thermostat stuff some insulation in this hole and cover it with a piece of tape. This will prevent drafts from affecting the thermostat.Has the heating anticipator been properly set by a qualified air conditioning and heating technician? The heat anticipator is on mechanical non-digital thermostats and needs to be set according to the amp draw on the heating control circuit. The heat anticipator offers a small amount of energy savings and prevents thermostat overshooting for you as it shuts off the main burners because the fan will continue to run and dissipate the heat which remains in the furnace or heat. Digital and programmable thermostats have built in heating and cooling anticipators which automatically set themselves with no manual adjustments. The mechanical thermostat needs a manual adjustment and you need a tool called an amp meter to determine the proper setting.