This is an older (~20 year old) carrier rooftop unit, approximately 20 tons. There are 2 compressors in the unit, each controlled by a 3-pole 600V contactors (with 24V coils).
Several times I've been there and there is a demand for cooling, with no compressors on. I have 24V (26V to be exact) at the contactor, but it's not closed. With a screwdriver I manually push-in the contactor and then it stays shut!
Ok not big deal, must be bad points. Sure enough they're finished, so I install a new one. Next day I'm back, and it's the exact same problem. 24V demand, but not closed, then when I push it in it stays on. Any clue what this could be??
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