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  1. #1

    Package unit PM in low ambient conditions

    Hello everyone,

    When performing PMs on rooftop package units in low ambient conditions, it's often necessary to jump out the thermostat at the unit to get it to come on. I was always taught to go from R to Y1 (energizes compressor) and R to G (energizes blower motor).

    First question: Why does the blower motor sometimes energize with just R to Y1?

    Second question: On a two-stage unit, is it unwise for any reason to jump the unit out so that both stages come on at once (in other words, R to Y1, R to Y2, and R to G all at once)?

    Thanks for the help!

  2. #2
    Join Date
    Jul 2003
    Location
    Orange County N.Y.
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    1,176
    Quote Originally Posted by HVAC_Austin View Post
    Hello everyone,

    When performing PMs on rooftop package units in low ambient conditions, it's often necessary to jump out the thermostat at the unit to get it to come on. I was always taught to go from R to Y1 (energizes compressor) and R to G (energizes blower motor).

    First question: Why does the blower motor sometimes energize with just R to Y1?

    Second question: On a two-stage unit, is it unwise for any reason to jump the unit out so that both stages come on at once (in other words, R to Y1, R to Y2, and R to G all at once)?

    Thanks for the help!
    Question #1. If the thermostat is set to the cool mode the Y1 and G are usually switched together internally at the thermostat.

    Question #2. I generally don't try to run everything at once. If the wiring and/or electrical panel is not correct, the inrush current could possibly make things hot, melt wiring, trip the breaker, or blow a fuse or 2. Better to err to the safe side of the equasion, don't ya know.

    ...Ron
    Roof Rat

  3. #3
    Join Date
    Jun 2004
    Location
    Olean, NY
    Posts
    1,446
    In what I've been seeing in the small packages the fan has been wired in to y1 inside the unit. I'm not sure what the most common setup is in these little guys but that's what I've been coming across.

    So has y2, some makes won't let you have y2 without y1. I just put both stages in the wire nut with r and if the fan doesn't come on, toss g on in there.



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  4. #4
    Quote Originally Posted by rscamaro View Post
    Question #1. If the thermostat is set to the cool mode the Y1 and G are usually switched together internally at the thermostat.

    Question #2. I generally don't try to run everything at once. If the wiring and/or electrical panel is not correct, the inrush current could possibly make things hot, melt wiring, trip the breaker, or blow a fuse or 2. Better to err to the safe side of the equasion, don't ya know.

    ...Ron
    That's a good idea. It's easy to want to run everything at once when you have 20 other 2-stage RTUs waiting on you! Thanks, Ron.

  5. #5
    Join Date
    Jul 2003
    Location
    Orange County N.Y.
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    1,176
    Quote Originally Posted by HVAC_Austin View Post
    That's a good idea. It's easy to want to run everything at once when you have 20 other 2-stage RTUs waiting on you! Thanks, Ron.
    I understand that you are a busy person, and I've been in your shoes. You want to make things a little easier? Design an engineered bypass, or boxed and switched jumper set.

    It takes one water proof box large enough to hold all the switches that you want for your jumper box, the switches, a 5amp circuit breaker, and enough colored 14/16 ga. wire and alligator clips for the leads. I liked to color code everything for ease of use. I've made a few for some newer techs. Pretty much everything can be found at Radio Shack except some of the more colorful wire.

    Making one will make your job quicker and safer than constantly having to pull single jumpers out and connecting them up individually. The downside is that it will be another tool to carry up to the roof.

    ...Ron
    Roof Rat

  6. #6
    Join Date
    Mar 2013
    Location
    Joplin,Missouri
    Posts
    310
    Some units automatically energize the blower on a call for cooling and some dont i agree with ron make a switch box it makes things much easier i usually will initiate a first stage cooling call and check first stage operation and then fire up second stage and check them one at a time thats my preference anyway

  7. #7
    Ron, that's a great idea. Are you able to provide any more details on how to make this (or pictures)? Hauling it up to the roof would be worth it when you have 20+ to do. (And my wife loves it when I spend money on projects like this...not)

  8. #8
    Join Date
    Jul 2003
    Location
    Orange County N.Y.
    Posts
    1,176
    Quote Originally Posted by HVAC_Austin View Post
    Ron, that's a great idea. Are you able to provide any more details on how to make this (or pictures)? Hauling it up to the roof would be worth it when you have 20+ to do. (And my wife loves it when I spend money on projects like this...not)
    Not a too difficult project. You'll need a suitable waterproof box, a 5 amp mini circuit breaker, 7 switches, a length of 8 or 10 conductor 16 guage t-stat cable, and 7 alligator clips.

    Pretty much you take the red lead and tie it to one side of the mini breaker, then from the other side of the mini breaker through the 1st switch, then set up the other switches and solder or connect the "red" through one side of all of them, the other sides of the switches you decide what colors and placement they belong, run the rest of the cable out and affix your alligator clips. I recommend larger clips as they will be easier to connect.

    Don't for get to mark the switches. Pretend that it is a manual thermostat and wire it as you would a standard heat pump stat.

    ...Ron
    Roof Rat

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