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  1. #1
    Join Date
    Jun 2005
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    3
    i recently purchased a home and noticed weak air-flow thoughout the house. When i pulled the cover off from infront of the inside condenser, i thought for a moment that the previous owner had installed filters on the underside of the coils. That was not the case however, for upon further inspection and a little prying i removed a 1/4 inch mat of dirt/hair/funk spaning the entire underside of the coils.

    While giving the coils some much needed attention i noticed a red lead comming from the blower motor which was just dangling down the side near the coils that had the end (metal push-on clip) electric-taped. I had the trusty ol' volt meter on-hand so i desided to see if this wire which was dangling so close (for who knows how long) to the squirl-fan was hot. I proceded to hook the wire with the end of my probe (mid-way up the wire on clean insulation) to get a better vantage on the end clip and my volt meter registered 120 volts. Mind you, this is just touching the outer insulation of the wire. For s&g's I tried the insulation on the remaining 3 wires comming from the motor and they registered 15-20 volts on the insulation.

    Now. Im not an electrician and most of my electronic know-how is focused on computers where 12 volt DC is about the worst burn im gonna get, but shouldnt the wire insulation be, insulating the current? And why is this red lead comming from the motor (yellow blue green are tied in with the relays above the blower) hot with 120v? Is this just the norm? Should i roll up the red lead and insulate it from grounding out?

    Thanks,

    Josh

  2. #2
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    It's the speed select wires from a PSC blower motor. Usually 3 speeds, and you connect the wire corresponding to the desired speed. Yes it absolutely should be insulated.

    If you are not sure about it, call an HVAC contractor or electrician.

    paul

  3. #3
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    you are working inside a unit which is energized? and you do not know about more than 12 volts? you are DANGEROUS/ HAZARDOUS!

    something of you explaination is not clear: getting a 120v reading in the middle of an insulated wire -- what was the other meter lead connected to? was the wire damp? call an electrician before you die!

    6 volts is enuf to kill -- it takes but 25ma & something in excess of 25mv to drive the amps thru the heart for electrocution -- not too many volunteers to get a good study --

    from 1968 statistics: 1000 accidental electrocutions, 500 were nonresidential, 250 were of QUALIFIED people (= they knew of the hazards & were trained); I believe 2 of those were linemen working on 120volt!


  4. #4
    Join Date
    Jun 2005
    Posts
    3
    cembsee:

    Of course im not working within a live unit. Forgive me for taking for granted that while i am not an electrician, electrical work is not rocket science, and common sence practices should be observed.

    After cleaning the coils i re-energized the system to check the wires. Yes, it is exactly as i explained. Im getting 120v reading from the outside rubber shielding on the red lead comming from the blower motor. The wire is dry and clean. My question was it normal for this (or any) lead from a blower motor to be hot.

    Thank you for your concern? (or stating the overly obvious lack of common sence your used to correcting)


    tecman:

    Yes, im aware that the selection of wires exiting (entering?) the blower motor are more than likely motor speeds. However, my question was why the red lead comming from the motor is energized with 120v. Quick checks with the other 3 wires show them to be dead when each one is disconnected from the system.

  5. #5
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,111
    Originally posted by crux
    When i pulled the cover off from infront of the inside condenser
    Inside Condenser? were would that be located?
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  6. #6
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,111
    Originally posted by crux
    However, my question was why the red lead comming from the motor is energized with 120v.
    Uh! Feedback maybe?
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  7. #7
    Join Date
    Nov 2003
    Posts
    501
    Originally posted by mrbillpro
    Originally posted by crux
    When i pulled the cover off from infront of the inside condenser
    Inside Condenser? were would that be located?
    Right here.

  8. #8
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,111
    0 OK stupid me I should have known.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  9. #9
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Originally posted by crux


    Yes, im aware that the selection of wires exiting (entering?) the blower motor are more than likely motor speeds. However, my question was why the red lead comming from the motor is energized with 120v. Quick checks with the other 3 wires show them to be dead when each one is disconnected from the system.
    Since the motor is most likely powered off of 240 volts, each leg will read 120 volts to ground. If the red lead is a speed tap, reading it with a voltmeter could well show 120 volts to ground, as it is tied to a power leg through a winding in the motor.

    paul

  10. #10
    Join Date
    Sep 2004
    Posts
    3,157
    Forgive me for taking for granted that while i am not an electrician, electrical work is not rocket science, and common sence practices should be observed.

    well lets see about that common sense. you Must have had the indoor condensor running with the power on to measure 120 volts on the insulation

    so what does your common sense tell you

    mine tells me that you have an induced current in that lead

    (oh yea , you dont get to much induced current with 12 volts do you?

    my common sense also tells me that I wouldnt be poking my hands around that wire, you have got a rattlesnake there ready to bite you and if it does you will be in for a big surprise,, or I should say 300 surprises

  11. #11
    Join Date
    Jun 2005
    Posts
    3
    tecman:

    Thank you, sir. The only experiance ive had with electrical motors are DC. pos in, ground in. In my ignorance i was baffled as to why i was getting current from a non-moving motor :P


    ct2:

    [ this space intentionally left blank ]

  12. #12
    Join Date
    Nov 2004
    Posts
    2,927
    Alot of the time only half of the circuit will be interupted to switch off the fan or compressor,or both.That means there will still be 120 volt there when the relay,switch,contactor,has opened.



    I hope that is an easy explaination...just tape up the loose lead,secure it out of the way and forget it.

    Always be careful.

  13. #13
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    HEY, induction = comes from changing CURRENT at ANY voltage -- lots of current = lots of induced voltage -- near by -- inversely proportional to square of distance!

    100 000 000 amps at 1 volt within 1 microsecond = lots of voltage -- probably get flash of lite as well --

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