HVAC Issue with Relays

Discussion in 'General Electronics Chat' started by DC_Kid, Apr 4, 2015.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
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    here's an issue i am trying to figure out as it all doesnt make sense to me. my hvac (heater & air handler in attic) keeps blowing edison fuse every few months. couple of years ago the control board fried, had ac guy come replace it, he said the motor might be on its way out. this time around i was digging in myself to see what the heck was going on. 1st was to measure the current in this York unit, with my General Instruments clamp meter i got the inrush and running amps. 30A inrush and then 14.8A running. these #'s match up to the two motors in the unit (an inducer for heat, and a 1hp blower motor). the motor is rated 1hp @ 14A 120v 60Hz. thats crappy efficiency, but nonetheless all the #'s seem to be on par with labels and what i measured.

    the unit is fed via 10/2 romex to a Bussmann fuse socket.

    ok, so i start looking and notice the Bussmann edison fuse socket with outlet is rated just 15A, the hvac unit has a 8ft 14awg cord/plug. doesnt seem so good for 14.8A running unit. i looked around inside the unit doors and found a few burnt wires at the crimp connectors (its all MIC stuff). i replaced the edison socket with a Eaton fused hvac disconnect, did hardwire using 12/2 cord (from disconnect directly to the control board, no wire nuts except for the gnd wire). i replaced the burnt wires (which were only 18awg) with some of the 12awg from leftover cord. cleaned connections, etc etc. everything went back and when the call for blower came on it just didnt go, about 0.2sec of starting and then quit. turns out two pins of relays basically vaporized.

    ok, so, i look at the board and note the path of the switched 120vac (see pic). oddly the fan blower is connected on the 10A relay side. this i just cant figure why. the motor is rated 14A, so why does it connect to a 10A relay?

    the burnt wires were a line-in wire, and a neutral wire to blower motor. burnt so bad i suspect they were restricting current during startup, and now that i fixed all that the current was allowed to move and the pins on the board fried off.

    i am wondering if they wave solder these board but if the solder time is low due to the small parts i am wondering if just not enough solder to wick onto the larger pins? to me the board design and wiring is just poor.......

    here's the pic (path of 120vac across the relays to motor)
    1 is the 30A relay contacts (SPST NO)
    2 is the 10A relay (SPST NO)
    3 is (WTF) a hair thin jumper, about the size of the wire on 1/4w resistor
    4 is the terminal to motor hot

    the PCB trace that is on the 30A pin burn, that goes to a "EAC" terminal, so wondering if i should connect motor here since its handled by the 30A relay.

    [​IMG]



    i am attempting to fix this board, new relays from Mouser just $5. a new board will be around $100 !!
     
    Last edited: Apr 4, 2015
  2. killivolt

    Active Member

    Jan 10, 2010
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    What motor is it; do you have the specs. I think that 14amps is if it locks up; in think 5 or 6 amp would be an average. It will spike momentarily until it's up to speed and then drop down when the start winding drops out.

    If you have a blower and belt attachment style the blower pillow block bushings could be bad. If the blower is directly attached to the motor shaft; the motor bearings could be failing. The relay board could be experiencing some cold solder joints and those can be re-soldered. It's possible the relay contacts are failing with the added load as well.

    kv
     
  3. #12

    Expert

    Nov 30, 2010
    16,278
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    Start with the basics. What size is the machine? Post some photos. How old is it that there would be an Edison socket in there?! Read the labels again. Notice the difference between RLA and LRA. Regular Load Amps, Locked Rotor Amps. RLA is an absolute limit for fan motors.

    And, yes, recent graduates have no wisdom. They believe the math and design relay boards that un-solder themselves. Still, no recent graduate would install a screw base fuse. What's going on here???
     
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  4. Brevor

    Active Member

    Apr 9, 2011
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    I once fixed a nearly new York furnace that had the same poorly soldered relays.
     
  5. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
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    i am thinking about installing a solid state relay setup to handle the main blower motor


    its a York unit GY9S100C20DH11J (5 Burner)
    1HP 115V 1075RPM 4Spd 48 Motor (direct drive)
    York motor part #024-32056-000
    motor amps 14.1 per nameplate of motor

    the edison socket is a Bussmann SRU item that is device local protection using type TL fuse. that contraption is now gone. everything installed was new ~8yrs ago (new home).

    this is a replacement motor "024-32056-000"

    [​IMG]




    some pics of the bad wires
    [​IMG]


    this is line neutral
    [​IMG]
     
    Last edited: Apr 4, 2015
  6. #12

    Expert

    Nov 30, 2010
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    The first thing to pursue is the excess current through the motor. It did NOT run for 8 years with an over current condition. Being labeled, "air over" means it's direct drive. The squirrel cage fan is connected to the armature (or rotor, if that's the right word). Obstruction of the air flow makes those motors use LESS current. Look for bad bearings.

    If you've been changing speed taps without checking current, look ashamed and put it back the way it used to be.

    Edit: Accumulated resistance in the power connections might lower the voltage available to the fan and thus increase current, but I have always seen it go the other way, excess current fries the connectors and melts the solder.
     
    Last edited: Apr 5, 2015
  7. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
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    #12, i am not following you. the motor is 1HP and labeled 14A, i measured about 14A on the wire. next is speed taps.... i didnt change any wiring locations, the only two wires that were burnt was a lineV(in) wire and a motor neutral wire. are you saying this motor should not be running at 14A ??

    i cant actually see the motor as it is buried behind a panel that holds the control board. to get in there means disassembling lots of other stuff.
     
  8. #12

    Expert

    Nov 30, 2010
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    Well, there is where I didn't read close enough.
    The procedure is to adjust speed upwards, as high as it will go and stay below the labeled amps with all the proper covers on the machine. If I saw 14.0 amps being used by a 14.0 amp motor, I would be scared my meter might be off by just a tenth of an amp because that's enough to trigger overheat safetys in the windings. If the motor hasn't been stopping by itself, you're probably safe.

    If the motor is safe, you just have a bunch of burnt wiring to fix...right?
     
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  9. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
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    To echo what #12 said..Fix the bad wiring connections, and I'd reflow those solder connections and see what happens.
     
  10. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    I'm wondering if you didn;t screw up the wiring. EAC stands for Electronic Air Cleaner. So, 10 A for that sounds about right and 30 A for the motor sounds about right. The series connection of a 10A contact and a 30A contact smells like magic smoke.

    The blower and EAC relay should basically engage at the same time, but they should not be series connected. The EAC terminal is a switched source of 120V for the air cleaner. That "piece of wire" might actually be a fuseable link for the EAC. It makes it a non-user servicable part.

    I see two small relays, one with a 12 VDC coil and one with a 24 VDC coil which, to me, is very ODD.
    What I MIGHT expect to see is the furnace board switch 24 VAC power to a definate purpose contactor somewhere else on the furnace. Who knows what they do these days.

    ==

    I'd consider a definite purpose contactor (HP rated) for the motor AND a properly sized bidirectional TVS diode on the secondary of the 24 VAC trasformer (seen by the secondary fuse). i.e. Between R and C. Your lucky the board is only $100.
     
  11. killivolt

    Active Member

    Jan 10, 2010
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    #12 is right.

    Maybe it's just me; but I can't see the motor running at 14amps? The wire you show labeled "Yikes" is connected to what appears to be a fan limit switch. If the contacts are bad or it's been cycling on it for sometime due to other issues I would replace it as well. But; first you need to find all the issues; replacing wiring and securing all connections is obvious; but what's making the motor run at it's limit is another all together different issue.
     
  12. #12

    Expert

    Nov 30, 2010
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    Just stopping by to sign out. I still don't know if this is a flammable fuel burner, whether it has a refrigerant system involved, what size it is, what part of the country it's in, or if I will ever see a schematic of it. I can't divine how it's supposed to work with all that information missing.
     
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  13. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    You have at least 3 variables: CFM (cubic Ft/min), Velocity (ft/min) and SP (static pressure).

    As the obstructions get larger (dirty filter) the SP increases. This is what the blower is working against. This causes the current to increase.
     
  14. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    A 1HP motor drawing 14A @ 120v exhibits an efficiency of ~ 44%...
    While I claim neither expertise nor experience with HVAC equipment, I, nonetheless, find this difficult to credit as acceptable --- Am I missing something?:confused:

    Sincerely
    HP
     
    Last edited: Apr 5, 2015
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    See post #6 air flow obstruction on a centrifugal impeller fan causes current to drop.
    Max.
     
  16. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    post #9, i did fix all the wiring, after that the relay pins melted.

    post #14, not sure, if the bearings are dragging then perhaps its bad, but the #'s are matching the nameplate for "AMPS". if it should not run at the nameplate amps then i have a bad motor. however, if the 14A is 6A over what it should run at then i would expect it to overheat and the motor over-temp internal would trip. in order for me to get to the motor it requires a bunch of PVC cutting which is in the way of access to the motor. i

    but, maybe its a bad motor, this online calculator says 10A FLA and 8A running
    http://www.engineeringtoolbox.com/electrical-motor-calculator-d_832.html

    i posted the units model #, its a York 5-burner natural gas unit with a AC expander unit piggybacked onto this unit.

    there are no air flow restrictions, the ducting (flexible insulated tubing) is all wide open.

    that "switch" component you see on that burnt wire i believe is a over temp limit switch.

    the motor has never locked up as far as i know.

    the "EAC" (not used, has a terminal cap on it) and the "Hi Fan" are switched 120Vac via the relays. it seems that the 30A relay contacts switch the 120Vac to the EAC terminal and into the NO contacts of the 10A relay. the board must turn on the 30A relay to get power into the Hi Fan terminal (via the small 10A relay). i might just use the EAC terminal for the motor, or, i will get a solid state relay.

    also, a 1HP rated motor 120Vac 60Hz (all US stuff) with PF ~80% will be around 14A if the motor is in that 50-60% efficiency range. i need to call a parts place to see if they can tell me the running amps of a replacement motor.
     
    Last edited: Apr 5, 2015
  17. killivolt

    Active Member

    Jan 10, 2010
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    This and

    this...... got me thinking.

    Like #12 said if it's a squirrel cage and it's before the intake; it will decrease mass air-flow and no air can be moving. If it's after the blower and Heat exchanger; like an obstructed evaporator that has never been serviced might cause increase pressure and load on the motor. It would also short cycle the fan limit.

    kv
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Same effect either side of Fan, reduced current due to unloaded fan.
    Max.
     
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  19. killivolt

    Active Member

    Jan 10, 2010
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    Correct would only occur with a complete blockage. A partial blockage will allow air to load; and a back pressure.

    kv

    Edit: Partial Blockage does not explain all the amps in question; it does serve to explain the possibility of a damaged wire at the fan limit.
     
    Last edited: Apr 5, 2015
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The same effect is commonly seen in water pump installations, if the inlet & discharge is wide open the current is maximum and in some cases get nuisance tripping of breakers & O/L's, the current is regulated by reducing the flow on the output until motor rated current is seen.
    Max.
     
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