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In vehicles that have manual heating, air conditioning and ventilation system, the blower motor serves to control the vehicle temperature through fan speed and air circulation. It does this by providing resistance to the blower motor circuit through a blower motor resistor when it is running at a low speed. The blower motor resistor works for all speeds except high speed, which is controlled by a relay on a separate circuit. The blower motor receives direct 12-volt power through the starter circuit when high speed is selected. If the high blower relay fails, the blower motor will not circulate air at all when high speed is selected while the remaining speeds still operate.
If you’re having problems with high fan speed on your car heating or air conditioning, then the problem could very well rest with the high blower relay. Our expert mechanics can check the voltage and determine if the relay is the problem, or perform other diagnostics to identify other issues that could be causing trouble with your car’s HVAC system. If it is deemed faulty, the high blower relay should be replaced.
This may not be a big problem in the summer, when you can always roll your windows down if you want to stay cool. But in the winter, you need high speeds for your car heater to keep you warm and defog your windows. It isn’t critical to have this fixed, but if winter is approaching, it might be a good idea to have it taken care of quickly.