MEP-018a tripping breaker

[Jim Kinler]

hello, i loaned this set out during resent hurricane. the fellow said when he tryed to start his 3 1/2 ton certral air it would through the breaker. he was only trying the central unit when this happened. it did the rest of the house ok. i know this set should handle this. ive had to change diodes and voltage regulators on these before but they didnt trip the breaker anyone have any ideas? thanks

[Wayne 440]

I would expect that 3.5 ton AC to draw around 100 amps when starting. There is probably nothing wrong with your set, it just "doesn't like" the 20+kw load.

[Jim Rankin]

lots of modern AC condensing units have PSC type compressors which do not have a starting switch and capacitor. The older types had 'em and drew less of a starting surge.

So there's a difference between 3.5 Ton units in the starting surge.

He could also have a weak capacitor on either type compressor that he hasn't noticed, yet. It may show up sooner rather than later.

[Jim Kinler]

thanks for replys, i dont know what type ac he has. my ac unit 4 ton says 26 amps running 46 start i think, so i thought it should have handled his. i had put put about 25 amps on unit and it did fine before he got it. got it back yesterday and havnt ran it yet. he put about 80 hrs. on it after the storm said it ran fine and ran everything else in the house. but with his ac unit the blower and possible hidden loads it may have been to much.

[panzerwillie]

I got one of those units in my house runing in natural gas and i have a old 3 ton unit that pulls about 45-50 amps on start up, and about 22 amps runing, i install hot start capacitors in the ac unit and it help plus i ran thick gauge wire between the gen set and my house which help, but most important i crank the AC firts and once is running the rest of the house follows and it does well, hope this info helps

[Jim Rankin]

The "boost" or hot start capacitor units are a packaged start capacitor and relay that is connected across the run capacitor terminals of a single phase motor. It can help the Permanent Splitphase Capacitor (PSC) type compressor or other motor the most, because these motors do not have a start capacitor and relay. A motor which already has a start capacitor and relay shouldn't get much boost from one, though I know refrigeration guys that will try them on any compressor they see that has ever had capacitor failure or problems starting.

They are primarily intended for situations where voltage is low at the compressor, but should help out when running on a backup generator as you describe.

[Jim Kinler]

i started gen. up yesterday voltage was 113. i had to turn the voltage adjust knob to the bottom quarter of the range to get 126. when it left i got 126 at about 1 or 2 oclock position. the unit has one of the older style voltage regulators, so i changed it out with a nos i had. i attached the 3 jumper wires as per instuctions on the reg. and attached the large plug. started up and got 103 no matter how i turned the adjust knob. after 3 min. lost everything. put the old reg. back in got 126 at about 5 oclock postion on the vol. adj. knob. the fuse was blown on the 120 volt receptical on the front control panel i know it was fine when it left. i have another new style nos reg. i would like to put in. do i have to also change out the voltage adust knob. iam just wondering if i had a bad regulator although it did look to be new. i dont wont to damage another regulator.

[Jim Rankin]

problem could be in the voltage adjust knob, not the regulators? Sounds suspicious to me.

[Rich Mc]

While inquiring about a missing regulator on one of my military units(5KW) at one of the big surplus houses the first question ask of me was; what is the ohmic value of the voltage control pot on your unit? then it was stated "If it is not the correct pot for the regulator you install you will have problems". I don't recall the details but I do recall the warning. I guess the regulators are not 100% interchangeable between different models.