Sears 4 HP 220v compressor (30 yrs old) throws belt off when starting.

by Rick Chilcote

The unit has served me problems whatsoever. Recently, it started throwing the belt off when starting. Still using the original belt. I changed the oil and still throws belt off. When I replace the belt it works fine until the next time I start it up and it throws belt again. Could it just be needing new belt? Tension is fine. Thanks

If the sheave alignment is good, and if the belt tension is OK (as you say), then what may be causing it is binding in the pump sheave. If so, that the motor sheave is turing to speed and the pump sheave is not, that may be the issue.

However, a new belt is a low cost check, and that's what I'd do first if this were my compressor.


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