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  1. #1
    Join Date
    Aug 2010
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    84

    Faster Blower Testing With Ammeter

    On some HVAC units, the blower wires connect to the back of the transformer (on older units). For this set-up and a few others, it is somewhat time consuming to test the voltage going to the blower.

    I wanted to use an ammeter to see if the blower is receiving volts. My thought is that if the blower is trying to start, I should receive a reading on my ammeter. How much of a reading would I get on a 1/3 (120 or 240 volts) blower reading if the blower was trying to start? I would use it on the positive wire and not wrap it around the ammeter. At least, this would give me a faster start in some situations.

  2. #2
    Join Date
    Dec 2005
    Posts
    114
    Wow are you


    He may be misthinking what he wants to do to help save time.

    But comments like that are helpfull at all.
    Last edited by beenthere; 05-08-2011 at 03:41 PM.
    Bob O. 84,Pa.

  3. #3
    Join Date
    Aug 2010
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    84
    Do you not see the benefit of testing the system this way? Don't you think this should work...

  4. #4
    Join Date
    Sep 2008
    Location
    Western PA
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    25,855
    Quote Originally Posted by jjrr007 View Post
    Do you not see the benefit of testing the system this way? Don't you think this should work...
    Not trying to be a jerk, but your wording indicates, to me at least, that you may not completely understand what you are doing. This makes me nervous.

    I wanted to use an ammeter to see if the blower is receiving volts
    Ammeters DO NOT check for voltage. Only current.

    I would use it on the positive wire
    Unless you are working on a DC circuit (which wouldn't be very likely) there IS NO positive wire.



    I also don't see where wires are going to be attached to a transformer. In most cases, the blower motor operates at line voltage.

    If you are employed in this trade, apply for professional membership and we'll be glad to help you more behind closed doors where home owners cannot see. It seems that you need more than a bit of guidance.
    Last edited by jpsmith1cm; 05-08-2011 at 11:21 AM. Reason: Fixed error and formatting.

  5. #5
    Join Date
    Mar 2011
    Location
    East Coast FL
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    1,065
    Sometimes jp a mfg will pick up a phase wherever they can , sometimes that is on the transformer line side.

    They do it to save wire.

  6. #6
    Join Date
    Nov 2004
    Location
    NJ
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    1,204
    Quote Originally Posted by jjrr007 View Post
    On some HVAC units, the blower wires connect to the back of the transformer (on older units). For this set-up and a few others, it is somewhat time consuming to test the voltage going to the blower.

    I wanted to use an ammeter to see if the blower is receiving volts. My thought is that if the blower is trying to start, I should receive a reading on my ammeter. How much of a reading would I get on a 1/3 (120 or 240 volts) blower reading if the blower was trying to start? I would use it on the positive wire and not wrap it around the ammeter. At least, this would give me a faster start in some situations.
    My guess is you are talking about the wiring coming out of the fan center. This makes sense as the wires may look like they are coming out of the back of the transformer on a resi furnace.

    You can't look for voltage this way, but amperage being presant will be an confermation of power (amps x volts).

    As to the actual value, who knows, and it will probably not be there for long as if you are having problems with the fan motor it is likely to be cycling on overload.

    I don't see any real value to this "short cut".
    Ed J

  7. #7
    Join Date
    May 2010
    Posts
    1,295
    I check the amps just to see if the unit I'm testing is getting power. If it isn't, then I switch to volts and troubleshoot from there.

  8. #8
    Join Date
    Aug 2010
    Posts
    84
    Thanks ZeroTolerance; tt's nice to hear that this method should work. I agree Ed Janowiak that it may only be there for a short time.

    Yes, I work in the industry and have been for some time I just wanted to reply to this message:

    Quote Originally Posted by jpsmith1cm View Post
    Not trying to be a jerk, but your wording indicates, to me at least, that you may not completely understand what you are doing. This makes me nervous.
    Ammeters DO NOT check for voltage. Only current.

    Unless you are working on a DC circuit (which wouldn't be very likely) there IS NO positive wire.

    I also don't see where wires are going to be attached to a transformer. In most cases, the blower motor operates at line voltage.

    If you are employed in this trade....
    * If you have a measurable amount of amps, you should have volts and that should give me some idea if the blower is getting power.

    * Yes, there is no positive volts in AC- I meant the black wire. (I had been working with DC often in my previous trade). It doesn't matter.

    * I have seen many situations where the blower is attached to the transformer. It is connected on the line side at the transformer and there may be a wire between.

  9. #9
    Join Date
    Oct 2004
    Location
    Central WA
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    1,582
    Quote Originally Posted by jjrr007 View Post
    Thanks ZeroTolerance; tt's nice to hear that this method should work. I agree Ed Janowiak that it may only be there for a short time.

    Yes, I work in the industry and have been for some time I just wanted to reply to this message:



    * If you have a measurable amount of amps, you should have volts and that should give me some idea if the blower is getting power.

    * Yes, there is no positive volts in AC- I meant the black wire. (I had been working with DC often in my previous trade). It doesn't matter.* I have seen many situations where the blower is attached to the transformer. It is connected on the line side at the transformer and there may be a wire between.
    Sorry, jjrr, but it does matter. When trying to help you diagnose or give advice and you don't use the proper terminology (or anything close to it) it can be difficult to visualize what you are talking about. It also gives the impression that you don't know what you are talking about even if you are very experienced. Assumptions are made that will effect the responses that you get.

    And yes, if there is current flowing through a motor that will not start there is obviously a voltage present. There are other things you can do, however. Seriously, apply for pro memebership for better and more complete advice.

  10. #10
    Join Date
    Nov 2006
    Location
    Southeastern Pa
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    If you want to check to see if a component has power available, voltage is the inly good choice. All you need is a winding or an internal protection device to be open and you can get a zero current reading. As a troubleshooting technique for a non-running fan, it is worthless.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  11. #11
    Join Date
    Aug 2010
    Posts
    84
    I will consider getting a Pro Membership. Thanks. From reviewing the thread, the only thing that was off was when I said positive. However, I am just trying to see if this method would work. The amps may be too low for this type of test, but its nice to hear others use it. Time is$ .

  12. #12
    Join Date
    Nov 2006
    Location
    Southeastern Pa
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    19,242
    If you want to save time, go right to the voltage test. See my post above. Start working on the Pro app today, because it takes a little time to process. Welcome!
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  13. #13
    Join Date
    Aug 2010
    Posts
    84
    Thanks. I see ur point about it not being a good test.

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