Many Techs have some confusion about ECM Motors and Systems - and no wonder - with as many as 21 wires going to these new motors, you cant just use a voltmeter anymore for proper diagnosis. "The prior generation of tools can help, but fall far short of giving the Tech complete information on why a system isnt operating correctly. " The VZ-7 is a microprocessor-controlled diagnostic tool that performs sophisticated testing with only 4 switches. With it, a Tech will be able to: ?? Visually monitor signal calls from the furnace/air handler circuit boards. ?? Interrupt those signals and send the motor any signals you desire, to observe motor operation ?? Get a visual display of motor RPM and the calculated CFM (on most systems) ?? Get a visual readout of all 4 system "taps". These selections help set up a system correctly ?? Get a direct readout of the control voltage in the motor (low voltage here causes erratic operation) ?? And finally, IF a problem is traced to the motor, one switch press starts an automatic anaylsis to clearly indicate if the problem is in the motors electronics, or one of 7 possible winding problems. GE, who makes a large share of these motors, reports that 41% of the motors returned to their factory actually have "no problem found". That means someone made an expensive mis-diagnosis; it also meand the real problem has not been corrected by replacing the motor. Almost any mistake in diagnosis on an ECM system will cost the Tech (or his customer) much more than this tool does! Two DVDs are included; one that teaches Variable Speed System Theory, the second instructs the Tech how to use the VZ-7 to troubleshoot these systems. ?? Microprocessor Controlled, but Easy-to-Use; only 4 switches. ?? Rugge