scrolls running backwards
Ok heres one that will stump you. Well it stummped me and my HVAC buddies anyways.
The lobby unit in our building has been running 24/7 for 3 years with no problems. Then one day out of no where we found the main breaker for the unit tripped. After a quick investigation we reset the breaker and the compressors sounded horrible. we assumed a mechanical failure, but threw guages on it anyways and found the pressures to be equal while the compressor was "running".
So heres where it gets interesting. The fan is rotating properly, however my boss decided to switch 2 of the 3 legs on the compressor to change its direction and what do you know, the compressor ran perfect!
Hopefully i gave you guys enough info. So what do you think, were stumped?
That crossed our mind, but if it was we cant pin point it
Originally Posted by jackintheboxtec
A scroll with a switched leg and running backwards WILL sound like a train wreck and won't develop a pressure diferential. The fan(s) are probably single phase motors and don't give a hoot.
If it ran for three years and suddenly something like that happened then somebody or something did a change up.
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The fans are actually 3 phase too, and running normally.
Originally Posted by Cooked
I guess i need to start thinking of all of the people i've pissed off lately
I have seen it years ago when the power company replaced a blown pole mounted transformer. They paced the 3-phase wire back differently. The phase shift on the wire change made it run backwards. It is not uncommen. Sometimes when the power goes out it happens.
I encountered the very same problem with a two stages Carrier RTU, one of the compressors ran backwards for five years or so, nobody notice it, I also thought the compressor was shot but after swapping leads it ran like a champ, amazing it survive after running backwards for so long.
Had a Trane unit do the same thing, one day the compressor was running backwards for no apparent reason, switched the leads and away it went.
Had the same thing with a 3 phase 7.5 hp blower motor.
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Back to back three phase motors running on single phase (bad contactor or breaker causing missing leg) will recreate the missing leg. Three phase motor would work on a single phase supply then
This is how one can use a three phase motor on single phase service.
I've seeing 3 phase motors running on 2 legs but as soon as the motor stops it wont start back up again,it hums,get hot trip or burn.
Originally Posted by timjimbob
The OP didn't state if it is 3 or single phase. Older single phase have been know to reverse after a "short" power blip. The is why they had a delay relay on them.
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Dear stumped, maybe it wasnt hooked up right in the first place..................
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"keeping condensing pressures low and evaporator pressures high"
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Maybe your boss knew what to do because he was the one who switched them the wrong way before you got there.
Originally Posted by engineerbrian