Temporary Wiring – How to Safely Temporarily Wire 120V

Assuming the North American electrical system, the only error that the electrician could make that would cause that symptom would be to swap the GND and HOT wires. Swapping hot and neutral would not do it.

That's a very serious error- and quite negligent in not checking for it, if that indeed is the problem. It could easily cause someone to perish.

If it is the problem you will be able to measure 120V between what you call the third pin on the two outlets.

It's also possible, but unlikely, that a problem with the PC could cause this symptom.

Edit: as others have pointed out, the PC functions so it can't be a simple swap, in fact no single error can cause these described symptoms.

If the hot is connected to both gnd and where it should go.. For example if the hot shorted to the conduit and the conduit gnd was broken.

Looking forward to a follow up on what this was...

Here is a guess as to what the diagram might be. It might be possible to figure out which wire is which and whether or not this diagram makes sense by careful measurement of resistance. I think I have the L-M-H sequence backwards.

More re resistance measurements etc.

To figure out which winding is which and which speed and voltage taps are connected to each winding, you need resistance measurements that distinguish very small resistance differences, perhaps 0.1 or even 0.01 ohms. If you can verify which wire is neutral and which winding is which, you may be able to run the motor, measure current and estimate speed to help determine the rest. Accurately (and inexpensively) measuring low ohms is a good subject to research.

If you can't find detailed information on the motor, you will also need to guess at the capacitor value. You will be able to find tables that give ranges based on motor power and voltage.

You might consider taking the motor housing off and carefully examining the lead wire routing, the connections to the windings and the winding wire size. Be careful doing that. The windings are somewhat fragile and there may be several washers on each end of the shaft that need to be in the right order. Those tend to stick either on the shaft (good) or on the bearing in the housing where they might drop off when you are not looking (bad). The bearings themselves may stay on the shaft or in the housing.

Without knowing the motor current rating, it may be difficult to know if you have everything right if you get the motor running. If you don't know why this motor was taken out or why the air handling system was scrapped, you don't have any reason to assume this is a good motor.