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I have 3 YJ 6 CFM pumps with the oldest being from 1996. The oldest is my favorite.

I just replaced the motor coupling this morning after 23 years.

I never shut the pump down under vacuum. You can draw oil into the pump internals. At least that’s my theory.

I also have a ball valve on my YJ micron gauge to prevent refrigerant from reaching the sensor.

Originally Posted by AJS HVAC

I have a newer yellow jacket vacuum pump model 93560. Been running fine and then yesterday did something weird.
I shut the pump off to change the oil, and also check micron rise. Went to restart pump and its locked up. Relieved some pressure off the pump and no change.
Reached underneah and rotated by hand. Would turn then lock up again. It started raining so put nitrogen on system to break vacuum and then checked it later.
I changed the oil rest of the way. Checked capacitor in it and tested ok. Plugged it in and started up no issues.
Returned this morning, hooked back up and all ok. Went to check micron reading went to restart and it wouldnt.
What is causing this to lock up after run time?

My YJ pump is 6 mo. Old and doing the same thing. Keep us post if you find a solution

I have an older super evac 8 CFM pump that doesn't pull as deep a vacuum as it used to. Does yellow jacket rebuild these pumps?

Right, sounded like a cap except that it tested good and caps do not usually come back to life. I know probably not but does it have brushes? Rotor position would show intermittent. When you turn it on in a non working state, does it buzz or try to run? Is it possible less that it has a loose part in the vanes of it is a rotary vane pump or a loose part like a dowel in the crankshaft or piston if it has that?

Yellow Jacket 93560 Vacuum Pump issue

I have a newer yellow jacket vacuum pump model 93560. Been running fine and then yesterday did something weird.
I shut the pump off to change the oil, and also check micron rise. Went to restart pump and its locked up. Relieved some pressure off the pump and no change.
Reached underneah and rotated by hand. Would turn then lock up again. It started raining so put nitrogen on system to break vacuum and then checked it later.
I changed the oil rest of the way. Checked capacitor in it and tested ok. Plugged it in and started up no issues.
Returned this morning, hooked back up and all ok. Went to check micron reading went to restart and it wouldnt.
What is causing this to lock up after run time?