Can anyone tell me what the AC diode sensor switch (the little
wafer with 2 connectors) that screws on to the end of the blower
motor in my 107 does? I couldn't get the blower to change speed, and
one of the connectors on this diode broke when I removed the wire to
check it. I soldered it back together, but now I can't get any
continuity reading across it. Thanks for any help.
On Thu, 28 Jul 2005 08:15:18 -0700, Robert Rittenhouse
Usually diodes in series with devices are used to protected the device
from power supply of opposite polarity But if one inverts the battery
polarity it's going to damage a lot of other things.
It can also be used to sense the current to the A/C by measuring the
voltage across the diode.
Measure the resistance of the diode disconnected from the circuit. It
should be less then 20 Ohms one way, then invert the leads an it
should be more than 100 Ohms.
In other words it must be almost a short circuit one way and almost an
insulator the other way.
You say that you have no current across .Are you talking about current
I get the impression that you mean voltage when you refer to current.
If you have about +12 volts on one side and no voltage on the other
side, the diode is defective or connected the wrong way.
In order to have current you must have a load.
On Thu, 28 Jul 2005 11:25:25 -0700, Robert Rittenhouse
I placed each lead from a multi-tester on one of the diode's fins and
set the mutli-tester to test resistance: i.e., when I touched the
leads together current flowed from one lead to the other through a
circuit that showed essentially no resistance. However, when I placed
one lead on each fin of the diode, the meter did't budge, regardless
of which lead i placed on which fin; i.e., no current flowed evidently
because there was essentially infinite resistance or an open cirucit.
Am i doing something wrong, is the diode bad, or cannot I not check it
On Fri, 29 Jul 2005 20:29:52 -0700, Robert Rittenhouse
Then , the diode is defective.
Someone has suggested that you can short the wires( the diode) and
everything will be OK. He is probably right but without knowing the
reason for the existence of the diode I can' t recommend it
To be safe, do not run the car's engine with a shorted diode.
If the diode is defective, why ? Did you make a short ? Old age ? Not
If the motor is defective you will burn the new diode.
You should be able to run the electric motor before installing the new
diode by connecting it directly to the battery. If it runs without
getting very hot ,then it's safe to install the new diode.
You could measure the current before installing the new diode but if
there is a short you probably burn the meter.
What I some times do is to temporarily install a 12Volts lamp (high
beam) in series with the circuit ( in your case replacing the diode).
If the light becomes very bright, measure the voltage at the lamp's
terminals. If it is 12 volts at one side and zero at the other side,
you have a shorted motor. If you have 12 Volts on one side and a few
volts at the other side and the motor slowly runs, it should be safe
to install the new diode.
If you want to go this way, install the lamp and report the type of
lamp you are using and the voltage at the terminals.
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