Does any one know how come a contactor is welding shut with in 3 to 4 months. Replaced it twice. It does have a mercury bulb or bimetal T=Stat.
CONTACTOR WELDING SHUT
MIREMEG
1 - 19 of 19 Posts
Replace stat with digital, that will limit the amount of cycling.
You need to check your low voltage, is it low? Is it 19V? Should be 24V or higher. Could be lots of reasons why it is low. Package unit? Wrong transformer tap being used 208/240V unit. Bad wiring? A chattering contactor will certainly do something like that otherwise check your loads but I doubt it is your loads.
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My question is how could it not be load related ? It takes amps to weld. I have seen plenty of chattering contactors not weld shut. Pit them up nice though.
It could be Ants, compressor drawing lock rotor, run cap UF off of spec. Yes the load welds it but if two contactors are new and welding closed a compressor drawing 18 amps on a 35 amp rated contactor is not going to weld it shut. He has points becoming very dirty to the point they weld.
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3,779 Posts
Did you check the t-stat?
Check the Heat anticipator on the stat or just change it to digital.
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1 Posts
Check the amp draw on compressor startup.
How does changing the heat anticipator setting affect the amount of cycling the contactor does in cooling mode?
Should have said cooling anticipator if applicable some have them some don't but it sounds like something is causing chattering, could just be no time delay and an out of calibration mercury bulb stat or something completely different.
Now have seen 4 welded shut, regular 2t to 5 t and the start amps seem the only reason, and OEM maybe out of 100million produced, etc...
Systems were / are normal and fine, but the contactors in the past few years are quitre different looking than (I think) the Minnisoata USA copper tabbed- and lugged ones.
Just last week "out of concern" removed 2 1996 contactors... dual compressor , first one 2 ton second 3 ton
Hydro-Temp had 40/50res in it, too-- because the first of three staging gets 65% to 70% of the cycles...
Now the new 40/50res are technically not the same surface area as those removed, exactly looking at everything making contact.
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A TDR in a stat does what when the voltage is lower then 18V or a switch is cycling?
A TDR in the unit at the contactor handles both. Make it a DOM and there will be no conflict with the stat built in TDR.
I am going with a crap contactor not seating properly on this one and/or amps due to start up/low line voltage.
These contactor troubles are on a giant toaster or the space shuttle?
Might help us to know, just sayin
A TDR in the unit at the contactor handles both. Make it a DOM and there will be no conflict with the stat built in TDR.
I am going with a crap contactor not seating properly on this one and/or amps due to start up/low line voltage.
These contactor troubles are on a giant toaster or the space shuttle?
Might help us to know, just sayin
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32,723 Posts
Space shuttle is retired, so I'm going with the giant toaster....A TDR in a stat does what when the voltage is lower then 18V or a switch is cycling?
A TDR in the unit at the contactor handles both. Make it a DOM and there will be no conflict with the stat built in TDR.
I am going with a crap contactor not seating properly on this one and/or amps due to start up/low line voltage.
These contactor troubles are on a giant toaster or the space shuttle?
Might help us to know, just sayin
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7,302 Posts
I'm thinking a 17 phase toaster as well
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8,098 Posts
The #1 cause is of new contactor point sticking/welding is using a contactor that's too small. A 20 amp contactor may work fine on a 2 ton unit, but it won't last more than a week on a 5 ton unit. The #2 cause is probably insects getting between the points. Chattering will also cause it, but this isn't as common as 1 and 2, and is generally noticable, that is, due to the racket it makes when this is happening. I'd rate it as the 3rd most likely cause. An overamping compressor is another possibility. I'd rank it as being less likely than the previous 3, but it definitely causes welded contacts on occassion. Locked rotor would fall in closely behind high running amps.
You'd want the contacts to slam into place. If the voltage to solenoid drops excessively due to source issues or long wire run, this can happen. You could add a new 24v transformer at the compressor unit, then use a small 1 or 2A relay controlled by original 24v line.
This maybe the best option if redoing wiring is not economical.
This maybe the best option if redoing wiring is not economical.
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