Question about Buick Century
The blower motor is a variable speed motor. The higher the voltage
applied to the motor, the faster the speed. Depending on the HVAC
(Heater Ventilation Air Conditioning) option installed in the vehicle,
blower speed control could be through a set of resistors or through a
solid-state blower motor control module.Battery voltage to the
blower motor is supplied by the heater & A/C control by way of the
blower resistor (or blower motor control module). At low and medium
speeds, the voltage is stepped down by the blower motor resistors. At
high speed, the blower motor relay is energized, removing the blower
motor resistors from the circuit. Battery voltage is then applied
directly to the blower motor through the relay. The motor will then run
at maximum speed.
Several types of HVAC systems were available on these vehicles, from manual to fully automatic electronic control. The blower motor speed can be adjusted manually by pushing the fan switch up or down or automatically by placing the heater & A/C control in the AUTO mode.
In general, this system is reliable. Because so many of the control operations are electronic, special diagnostic equipment really should be used for system diagnostics and check-out. An authorized technician using a scan tool can most quickly locate HVAC problems.
Fig. Typical behind-the-instrument panel view of HVAC related components. Depending on the HVAC option, not all components are used on all vehicles
Fig. Typical HVAC operation schematic
An inoperative blower motor could be caused by the following:
Blown fuse(s). The fuse should be replaced. There may be both a LOW BLOWER and HIGH BLOWER fuse. Some models may also call it the HVAC fuse. Even the RADIO fuse is used in some applications. Check them all. If a fuse is blown there may be a short to ground in one of the power supply circuits. Open Circuit. Check the circuit between the ignition switch and the blower motor, and the blower motor ground circuit. Repair as necessary. Faulty blower switch. A faulty blower switch should be replaced. Most heater blower circuits also include a blower motor relay (look in the underdash convenience center), as well as a blow motor resistor. These items should be checked especially if the blower runs in one or two speeds, but not all speeds selected.
The blower motor resistor is located on the back of the blower motor housing under the dash on the passenger side. It can be difficult to get at, but it is doable. Be ready with the ibuprofen the next day for your sore back.
Remove the cover panel from beneath the dash on the passenger side.
Unplug the power 'ribbon' wires leading to the resitor.
Unplug the wires that lead from the resitor to the blower motor housing. There are usually two, one black and one purple that share the same plug.
Remove the short hose that leads from the blower motor housing to the ventilation system ducts.
Remove the blower motor by removing the three hex screws that hold it in place.
Remove the resistor by removing the three hex screws that hold it in place. The resistor is right against the firewall so two of the screws are very difficult to reach. A slender flexible socket extension will make the job easier.
Attach the new resistor in place using the same hex screws. Only 1 or 2 of the original three are needed (the part is very light) if you do not feel like fighting with the ones next to the firewall.
Reatach the blower motor and reconnect the hose.
Plug the power cable wires back into the resitor and the wire from the resistor back into the blower motor.
Instead of hex screws mine were held in with 7/32 bolts. It was difficult, but easier than I had anticipated. I replaced two of the three bolts holding the resistor. The blower motor came with instructions saying that the plugs may have to be cut off of the resistor and the blower motor, then spliced together... I had to do this on mine.
I got everything back together and now the fan works on four of the five levels. It does not work on high.
I found on another site that said "high" uses a different circuit, with a separate fuse. I found the fuse panel on the passenger side of the dash when the door is open. The cover for the panel has all of the fuses mapped out, so it was easy to spot the 25 amp "Blower High Speed" fuse. I was very impressed to find the panel contained a fuse puller and replacement fuses. Mine was blown, I replaced it, and all is good with the world.
Posted on Sep 08, 2010
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Posted on Jan 02, 2017
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