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res split system works depending on time of day?

yup, i have the old parts here in hauppauge - (hauppauge industrial park) & you are more than welcome to them (cause otherwise they're going to visit mr trashman). see attached photo. [if you want, i'll send you an email with my specifics.]

if you haven't spotted it already, you'll note the fried & melted contactor coil - it obviously wasn't very happy. as a note to my last post, that should read that the xfrmr primary opened not the secondary.

as to why the primary would open before the secondary - that may really be a toss-up - i've seen it happen both ways. the popular residential 24vac xfrmr is rated at 40VA. in these parts, we typically see a line voltage of ~124vac - that usually translates to about 26.5 vac on the secondary. that's done on purpose by the manufacturer to ensure that in a lower voltage locale or brown-out situation that even down to about 112-113vac the xfrmr will still generate about 24vac in order to satisfy the pick-up voltage requirement of the contactor coil. with a typical secondary voltage of 26.5v and a line input of 124v that translates to a xfrmr turns-ratio of ~4.679. if the xfrmr is rated at a 40VA and is operating at 26.5v on the secondary then that provides an available current of 40/26.5 = ~1.51 amps at the secondary and (1/4.679 x 1.51a) about ~.32amp or almost 1/3amp @ 124vac on the primary side. if the secondary attempts to draw past the 1.5a, the primary coil will attempt to supply it right up to the ~1/3amp current carrying capability of the wire that actually comprises the primary coil. at that point it's only a crap shoot whether the primary or the secondary gives out first - unless the manufacturer specifically designed it such that primary coil will always open first which could be the case here. the secondary side of the xfrmr typically 'sees' a much harsher environment during the actual closing of the contactor coil (therefore harder to estimate the proper fusing) so it's possible that the manufacturer intended that the primary fail-open first safety & reliability-wise.


ss

Comments

  • soot_seeker_4
    soot_seeker_4 Member Posts: 22
    res split system works depending on time of day?

    i haven't visited this complaint yet but lady claims that 2.5yr old 2-ton resd split system will work all day if turned on in morning (when cooler) but will do nothing (not even fan) if turned on in the afternoon. she also mentioned that it seemed to slowly deteriorate to this point over the past 2 months. i think i've seen this before but i don't want to influence anyone's answer / thoughts.

    what say you?

    ss
  • bill_51
    bill_51 Member Posts: 27


    sounds like she doesn't know how to use her programmable thermostat and someone goofed around with the programs on her
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Could very well be a...

    Could be a start-up issue. Be sure to check the operating charge and be sure to check the quality of the refrigerant. Quite often, systems that have not been properly evacuated and/or charged will work when the heat loadis low, but will fail to work when the heat load increases.

    I would not give too much credibility to the fan issue as that may simply be the customer's perception about "the sytem not working at all".

    Keep us posted.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Any Word?

    What happened on this call?
  • soot_seeker_4
    soot_seeker_4 Member Posts: 22
    on vacation

    waiting.

    they're not back til after the 26th.

    ss
  • soot_seeker_2
    soot_seeker_2 Member Posts: 228
    any further guesses? - i fixed it yesterday....


    any further guesses?

    i fixed it yesterday.

    she was right. no fan operation either. t-stat fine - basic non-prog - buzzed out fine.

    york 2.0 ton - furnace- a/c air handler in attic - 2 years old - R22 - 10 seer - uses typical texas instruments ignition control bd for both sides - control board was fine.

    ss



  • Mitch_4
    Mitch_4 Member Posts: 955
    my guess

    is something odd..like a nest of earwigs that was inactive in the cooler morning, and active as the day got hotter, and they would sit between the contactor points.

    (Just kidding)

    Overcharged, or very dirty condenser coil, and the high head pressure control would stop the unit from running after the ambient temp got warm enough to drive the pressure up.

    M
  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845
    Did somebody by chance...

    Maybe wire this furnace up across an attic fan thermostat so that when the attic got to hot the t-stat would close to activate the fan, but would break the power to the furnace?
  • jeff_51
    jeff_51 Member Posts: 545
    this thing isn'nt by chance wired through a saver switch???

  • soot_seeker_4
    soot_seeker_4 Member Posts: 22
    don't wanna drag it out -

    ok, it wasn't all that exciting.

    this unit uses a (working) 2 yr old furnace control bd that unlike the latest ones doesn't include any fuse protection for the 24v xfrmr secondary loop feeding the contactor coil - if it did, this problem would have been obvious a couple months ago. instead, the contactor coil essentially melted to a slow death over time & temperature (made in china) & finally killed the xfrmr up in the A/H. replaced both the xfrmr & contactor and all was well again. it's possible that the utility company voltage sags on hot days played an elusive part in this too.

    ss
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Fuses?

    When you replaced the transformer did you install an in-line fuse on the low voltage side?
  • don_156
    don_156 Member Posts: 87
    Now

    Come on professor,we try to keep it at job sercuity dont you know.

    However I agree with the secondary fuse,I seen low voltage wires act the same way when missing some of its coating.

    Replace the transformer and a month would go by and it would blow again.

    We carry the tranformer that have the reset button,alittle
    more cost,but it saves your butt on a night call and you just used the last one.

    I have a question..did it burn the primary side or the secondary side of the transformer?

    And if the short was on the secondary side,why did it burn
    out on the primary side?
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Job Security

    On all of our contract systems, I required our guys to install inline fuses on all transformers. We also tried to keep a box of replacement fuses on the job, but out of sight of a curious equipment owner. I figured that a 39-cent fuse was cheaper than a $20 transformer.

    I am personally also a fan of the transformers with the reset button, but find it easier to keep multi-tap transformers on the truck, which reduces the number of parts on hand.
  • soot_seeker_4
    soot_seeker_4 Member Posts: 22
    replacement xfrmr..

    actually i replaced the xfrmr with a hefty white rogers s1 series which has the internal thermal protection - auto reset (it's also multi-tap). the protection turned out to be a good thing too since the contactor coil then tried to take out the new xfrmr in the first 5 minutes. the xfrmr shut itself down & auto-reset in about 3 minutes. i then turned off the system & changed out the contactor after seeing the burnt / melted coil. must have been a bad day at the factory for refilling the wire insulation tank cause that coil looked pretty bad. and yes it was the xfrmr's primary side that opened. like i mentioned, the new version of these boards are now fused on the secondary loop through the relay - let's see how many of these boards just get thrown out for the sake of an unchecked fuse. btw, they're using 'car style' u-shaped color fuses on those boards now so it pays to have a pack of 1-5 amp types handy when you're up in a hot attic.


    ss
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Old Parts

    Do you have the old transformer?

    I am always asking friends in the industry to give me the old stuff so I can make use of it in class. I can always get shiny new stuff, but the busted stuff is harder to come by.

    I always like my students to see system components after years of use and abuse.
  • soot_seeker_2
    soot_seeker_2 Member Posts: 228
    old parts..... see picture....

    old parts..... see picture....

    yup, i have the old parts here in hauppauge - (hauppauge industrial park) & you are more than welcome to them (cause otherwise they're going to visit mr trashman). see attached photo (sorry it's big). [if you want, i'll send you an email with my specifics.]

    if you haven't spotted it already, you'll note the fried / melted contactor coil - it obviously wasn't very happy. as a note to my last post, that should read that the xfrmr primary opened not the secondary.

    as to why the primary would open before the secondary - that may really be a toss-up - i've seen it happen both ways. the popular residential 24vac xfrmr is rated at 40VA. in these parts, we typically see a line voltage of ~124vac - that usually translates to about 26.5 vac on the secondary. that's done on purpose by the manufacturer to ensure that in a lower voltage locale or brown-out situation that even down to about 112-113vac the xfrmr will still generate about 24vac in order to satisfy the pick-up voltage requirement of the contactor coil. with a typical secondary voltage of 26.5v and a line input of 124v that translates to a xfrmr turns-ratio of ~4.679. if the xfrmr is rated at a 40VA and is operating at 26.5v on the secondary then that provides an available current of 40/26.5 = ~1.51 amps at the secondary and (1/4.679 x 1.51a) about ~0.32amp or almost 1/3amp @ 124vac on the primary side. if the secondary attempts to draw past the 1.5a, the primary coil will attempt to supply it right up to the ~1/3amp current carrying capability of the wire that actually comprises the primary coil. at that point it's only a crap shoot whether the primary or the secondary gives out first - unless the manufacturer specifically designed it such that primary coil will always open first which could be the case here. the secondary side of the xfrmr typically 'sees' a much harsher environment during the actual closing of the contactor coil (therefore harder to estimate the proper fusing) so it's possible that the manufacturer intended that the primary fail-open first safety & reliability-wise.



    ss


    Attachments:
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Hauppauge?

    Great! I'm in Brentwood.

    Why don't you pass by the college for the 10-penny tour?!

    Office number: 631-851-6897
  • soot_seeker_2
    soot_seeker_2 Member Posts: 228
    parts follow-up..

    i'll keep the parts in a box on the truck for you. i just need to find a quiet moment to get down there (south on wick's rd & make a right?). maybe on a wednesday evening if that's when you have class over there. i need to know roughly when and which campus building. things should quieter here hopefully after the 20th or so.

    ss
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    No problem Here

    I am on campus Mondays, Wednesdays, Thursdays and Saturdays. Just drop me an email and I will repsond with times, locations etc.

    Thanks again.
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