Intermittent HVAC blower motor operation

[YotaWagon]

I'm trying to diagnose my blower motor issues. The fan spins but it cuts out repeatedly during operation and will sometimes surge as well. The setting for the airflow doesn't seem to change the condition. The blower motor itself is a known-good unit.

I believe I need to test and possibly replace the blower motor control relay, but I'm an electrical dummy. Is the FSM telling me to backprobe the connector while the blower motor control relay is plugged in and note the voltages based on the blower speed switch position?

 

[Malleus]

Yes

 

[Malleus]

Sorry, that was too terse. You'll need backprobe leads on your multimeter, to ensure that you are actually contacting the rear ends of the terminals, and not just the insulation. They're the ones that look like needles.

You DO NOT want the "wire piercing" probes. If you cut the insulation, you're introducing problems later in the day. IMO, these things are the evil offspring of multimeter probes and vampire taps.

 

[YotaWagon]

Sorry, that was too terse. You'll need backprobe leads on your multimeter, to ensure that you are actually contacting the rear ends of the terminals, and not just the insulation. They're the ones that look like needles.
View attachment 4045782
You DO NOT want the "wire piercing" probes. If you cut the insulation, you're introducing problems later in the day. IMO, these things are the evil offspring of multimeter probes and vampire taps.

No problem, and thanks for the follow up. I was planning to get the backprobe leads for the multimeter.

 

[Malleus]

Love the avatar