The time I used a cheap multimeter versus a Fluke on a fridge compressor

I had a call last month over in Oakville for a fridge that wasn't cooling. Pulled out my old $15 multimeter from Harbor Freight and it was showing 120 volts at the compressor. After an hour of chasing my tail, I grabbed my buddy's Fluke and it read 108 volts. That cheap meter was off by a mile, and the compressor was bad all along. Has anyone else run into this kind of headache with low-end test gear?

2 comments

2 Comments

samthompson9d agoMost Upvoted

And the thing nobody talks about is how cheap meters handle voltage under load versus no load. Your Harbor Freight special was reading open circuit voltage just fine, but the second that compressor tried to draw current the cheap meter couldn't handle the sag. The Fluke reads true RMS and actually accounts for the waveform distortion from a failing compressor. I had basically the same thing happen with a well pump where the cheap meter showed 240 but the pump wouldn't run. Borrowed a friends Fluke and it showed 205 volts under load. Now I keep a decent clamp meter in my truck just for motors and compressors. You really can't trust those budget meters for anything with a inductive load like a fridge or pump.

the_blair8d ago

Hold up though, that voltage sag thing is real but I gotta ask something. Did you check if your cheap meter was actually fused properly? I've seen those HF specials with no fuse at all or a fake one that does nothing. A bad fuse or no fuse can give you all sorts of wack readings especially on inductive loads like compressors. The Fluke is protected right, so it reads steady. But a cheap meter with a blown or missing fuse might just float around and lie to you. Did you pop the back off yours and look?

-1