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Isolating and Replacing Problematic Relays
By Mike Bumbeck/
Printable version
Degree of DifficultyModerate
Estimated Time180 minutes
180 minutes
Coursing through the copper, inside a myriad maze of wires stuffed into the nooks and crannies of the modern automobile is the electricity required to run primary systems such as the starter motor, and secondary gadgets, like heated rear view mirrors. Since different levels of electrical power are required for running some devices over others, the automobile incorporates a relatively old-school electromechanical device to activate more modern innovations.
Isolating and Replacing Problematic Relays
Passing on the Power
This device, known as a relay, is essentially an electromagnetic switch that acts the same as one runner passing a torch on to the next in a "relay" race. When activated, the relay passes the signal on to send electricity flowing either this way or that—and the race begins. Insofar as automotive applications go, the relay usually passes the torch onto a bigger, faster, more powerful runner.
The good majority of relays in automobiles are used to channel a small amount of power in one circuit in order to trigger another, requiring a large amount of power, such as the tiny little electronic switch on a cabin climate control computer that activates the big old electromagnetic clutch on an air conditioning compressor. That being said, even fancy computers in modern cars still rely on the old-school electromechanical relay in order to make things work.
Recalcitrant Relays
For various reasons, not the least of which includes turning on and off thousands of times, and spending life in an environment that is alternately baking hot and freezing cold, relays may eventually stop working. When this happens, the switch to activate the heated seat may work fine, but the switch signal will stop at the relay and the big electrical power needed to heat up the coils under your hiney to keep your keister cozy will never be reached.
Worse, the engine heat can occasionally cause a relay to act on its own with complete disregard to switch commands, sending electrical power pell-mell. A malfunctioning relay can also cause the most difficult of all electrical problems: one that occurs intermittently, and at random.
Errant electrical power can, at the very least, cause things not to work and can, at worst, be downright dangerous. An electrical circuit switching on all by itself can overload and create an electrical fire. Intermittent electrical problems are extremely difficult to trace but can often be narrowed down to a recalcitrant relay. Other examples of failed or failing relays can be fuel control micro switches, horns not working despite valiant added hand signals, or a radiator fan not switching on when the coolant reaches a certain temperature.
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