FAN DOESN’T RUN - The furnace fires, but the blower does not start. After the burners have ignited, the next step in the heating cycle is starting of the blower motor.  This will be done either by a heat-activated switch or internal timing of a control board.  In either instance, the blower motor should start within 30 - 90 seconds after burner ignition. If the fan motor does not start, the furnace will overheat and the high-temperature limit switch should cause the burners to shut-off. Bad Blower Motor - Qualified Technician Recommended Heat-Activated Fan Switch - Qualified Technician Recommended Control Board - Qualified Technician RecommendedThe blower motor relay is the electrical switch that is used to supply the power for the vehicle’s blower motor. The blower motor is the component responsible for pushing air through the vents of your vehicle’s heating and air conditioning systems. Without it, the AC system will not be able to circulate the heated or cooled air.

The blower motor relay controls the current used to power the blower motor, and is subject to the constant on and off switching. portable ac unit for a vehicleOver time, it will eventually wear out. ac indoor unit cleaningWhen the blower motor relay does begin to fail, the vehicle will usually display a few symptoms that can alert the driver of a potential problem that should be serviced.average cost for 4 ton ac unit 1. Blower motor does not function One of the first symptoms of a problem with the blower motor relay is a blower motor that does not function. As the relay is the switch that supplies current to the blower motor, if it fails internally, then power may be cut off from the blower motor circuit causing the motor to no longer function.

One of the first symptoms of a bad or failing AC blower motor relay is a blown AC blower motor relay circuit fuse. If the blower motor relay develops any sort of problem that hinders its ability to properly limit and distribute power, it may cause the blower motor fuse to blow. Any sort of electrical spikes or excessive current from a bad relay will blow the fuse and cut power in order to protect the system. Another, more serious symptom of a problem with the blower motor relay is a burned or melted relay. Relays are exposed to high current loads and can sometimes get hot when they develop problems. In serious cases, the relays may heat up to the point where the interior components and plastic housing of the relay will begin to melt and burn - sometimes even causing damage to the fuse box or panel as well. Since the blower motor relay is essentially the switch that directly controls power to the blower motor, the entire AC system will be left unable to distribute its cooled or heated air if the relay fails.

For this reason, if you suspect that your blower motor relay is having a problem, have the vehicle’s AC system diagnosed by a professional technician, such as one from YourMechanic. They will be able to determine if the car will need a blower motor relay replacement, or another repair, to bring full functionality back to your AC system.Most cars equipped with a manual heating, ventilation and air-conditioning (HVAC) system use a blower motor resistor to control the speed of the blower motor fan. The blower motor resistor is used to reduce the fan speed in lower settings (1,2 and 3). Some minivans and SUVs equipped with a separate heating and air conditioning system for the rear passengers use a separate blower motor resistor to control the speed of the rear blower motor fan. Usually, a blower motor resistor is installed inside the HVAC system so that air flowing through the HVAC system cools down the resistor. Due to constant heating and cooling, as well as with a moisture present in the air, some parts of the blower motor resistor can corrode, causing it to stop working.

The most common symptom of a failed blower motor resistor is when the fan works in "High" speed, but doesn't work in some lower speeds. The highest speed setting may still work because in most cars in the highest fan speed settings the current bypasses the blower motor resistor (see the diagram below). In some cars, if the resistor is failed, the fan may stop working completely. Another reason a blower motor resistor may fail is when the blower motor has a mechanical problem or when a foreign object jams the blower motor fan blade and prevents it from spinning freely. This leads to increased current through the resistor and causes it to overheat and fail. In most cars, replacing the blower motor resistor is not too difficult. For example, in the 2001 Toyota Camry, it can be done within 15 minutes, the part can be purchased for $25-45 online. The resistor is installed near the blower motor underneath the passenger side of the dashboard. In some cars (e.g. Dodge Caravan, Ford Escape), the glove box needs to be removed, to get the access.

Read about testing the blower motor resistor on the next page.A furnace blower motor is one of the most important components in your gas or oil furnace. Consider that the purpose of gas furnace is to warm the home, and realize that it is the blower motor that actually takes that heat and directs it from the very isolated, insulated furnace and in to the actual home. If you’re having problems with the blower motor, you’re not only left wanting for heating in your home, but you’re wasting energy as any gas you burn and heat your furnace creates that isn’t actually channeled in to the house that needs it is pointless. Tip: A gas or oil furnace can be a matter of survival in cold winter areas. Try to do a maintenance check for this and other issues during the autumn months so you have time to respond and fix anything before you desperately need the heat. One of the most common problems is that the blower motor makes a humming sound. When it has cooled down to a safe temperature, check the motor.

Like with many devices that are in motion regularly, the humming could be the result of something as simple as improper lubrication. To determine if this why your blower motor hums, try lubricating the motor but don’t overdo it. Then restart the blower motor and listen. If the hum persists, then so do you. When your furnace blower has warmed your house to the set temperature, it begins to run on a slower speed. This is a normal energy saving mechanism that the motor is supposed to employ. But if your blower motor slows down unusually and makes a humming sound when it has slowed down, it might be due to a fault in the capacitor and the motor. Check your motors amperage draw using a tool that reads electrical current such as a multi meter and then check the rating on the plate of your motor to see how much is required. If the draw is more than the required amount, it’s an indication that your motor is working extra hard just to work normally. You will have to replace the motor and the capacitor.

This problem in your blower motor may have been caused by dust and dirt in your filter. If your furnace blower motor hums when it’s switched on but at the same time does not actually turn, the capacitor may be damaged. This problem of getting a humming noise along with little to no spinning is very common with motors that do not have good quality capacitors. You should replace the capacitor with a good one and the blower motor will work smoothly. Once again, this may initially trace back to a simple blocked filter. If your motor does not run even after replacing the capacitor, it is most likely that the unit overheated. You should reset the safety buttons located at the side of the unit. This is usually caused by the wrong adjustment of the pilot light of your blower. Readjusting it to an appropriate level should solve this issue. If your gas burners are dirty, they will give out a low sound that may sound like something between a low rumble and a hum. Cleaning, adjusting or replacing them will make the irritating sound go away.