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  1. #14
    Join Date
    Jun 2005
    Posts
    28
    bbk,

    Does your reply of waaaayy mean that yes we could have burned out 1 fuse? When that happens the unit will try to start but can't? Excuse my ignorance if the answer should be obvious. I am trying alleviate my ignorance. I am an engineer but it is chemical and not electrical.

    Mike

  2. #15
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    The installer will know. A tech can let you know as well. You'd have an HVAC contractor install it if it didn't come with one. I carry a few on the van myself. It takes just a few minutes to put in. Even if it doesn't help this problem I'd probably leave it in (barring any goofball interactions that I'm not aware of between a generator and a KickStart).

    The only way I know that a 220 AC could run or try to run on 110 with a blown fuse is if you have a short to ground in the unit. I have seen that before. I watched fan spin at a reduced rate while the compressor did nothing. But that was on an ancient system. We'd hope your brand new one didn't do the same.

    [Edited by Irascible on 06-06-2005 at 08:23 AM]

  3. #16
    Join Date
    Jun 2005
    Posts
    28
    Irascible,

    Thanks again. I have not had any problems up to now running the unit off of the old generator. I am highly interested in the kick start type of unit and have read of people installing motor start capacitors referred to as soft start capacitors to ease motor start draw for motors run on generators.

    Mike

  4. #17
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,423
    Mike
    Are the breakers off when you start the generator?

  5. #18
    Join Date
    Jun 2005
    Posts
    28
    pecmsg,

    I would say that the breakers are on when I started the generator. The generator had been running for a significant period of time before I turned on the AC and found I had this problem. The AC was in mode = off. I then switched the AC to mode = cool. It has a two minute (I think this is choosable). The blower motor then came on in the indoor portion (what I refer to as the furnace blower) and then it tried to start up the compressor and just wouldn't start. A spin or two on the outdoor fan unit and then nothing.

    Mike

  6. #19
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,423
    First get in the habit of starting the generator with all the breakers off. Circuit boards don’t like low and high voltage. ( TV / Microwave / Radios / Phone Etc.)
    Second get a voltmeter and learn how to use it.

    It sounds like you blew a fuse outside, but can’t trouble shook on a computer. Call your contractor to have the unit checked. Ask that he have a hard start kit on the truck. Good Luck

  7. #20
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    One question, when you say the compressor does not start, what happens ? Do you blow a breaker or does the compressor sit there and hum ?

    What may be happening is that the new generator may not have as much "reserve" as I will call it to start the compressor. The ability of a generator to handle a start surge like that depends on the available torque (mostly inertia at that point) and the peak capacity of the generator. This capacity is a function of the amount of iron (laminations) and the winding wire size. Most newer generators are made right to spec, no extra so to keep cost in line with company profits. If the iron (laminations that carry the magnetic field) is at the limit, the magnetic field in the laminations saturates, and no more power above saturation can be drawn. If the copper (windings) are at the limit, the wire resistance will limit the available output current. I suspect both factors are in play. You should see a momentary voltage dip as the compressor tries to start, and as you said the engine does not lug. This would indicate a generator limit. The older mil unit was most likely built with more generator reserve, either because it was older and things were designed more conservatively, or it may have had as part of the spec the need to handle greater surge loads.

    A hard start kit may help. Also the wiring to the compressor may be contributing a bit as well, since under these conditions any additional voltage drop might be just enough to tip the scale. If possible try to get some min voltage readings at the generator and at the compressor unit. Most Fluke digital voltmeters can measure min/max voltages and will capture the dip in voltage. If there is a significant difference between the generator and compressor, up the wire size.

    paul

  8. #21
    Join Date
    Jun 2005
    Posts
    28
    Tecman,

    Thank you for the reply.

    What happens is it seems like it tries to start and then quits and this is very quickly. I was outside last night watching the outdoor unit when it tried to start. I would say the fan turned a couple of revolutions and then nothing. No humming. The digital thermostat blinks cool when you first turn it to the cool mode from the off mode. I think it has a 90 second or 120 second delay mechanism. Then the blower fan turns on and then the compressor starts. At this point the thermostat quits blinking cool and just reads cool. Whne I turned the thermostat to mode=cool it started blinking cool just like it should. Then the lower kicked in after a delay and then the compressor tried to start and the fan outside did the couple of revolutions and then it just quit. I went back in and the blower kicked off and the light went back to blinking and it was ready to go through its delay and try again. The 30 amp 240 volt circuit breaker in the house did not trip. Some folks here have indicated that one of the fuses at the outdoor fuse holder may have blown and to check it.

    Mike

  9. #22
    Join Date
    Jun 2005
    Posts
    28
    Tecman.

    How much difference does the hard start kit typically make on these motors? Is it a cheap enough type of add-on that it is worth trying just as a matter or course. I know we don't discuss specific prices here but I am trying to see if the order of magnitude suggests just automatically adding one for ease of operation.

    Mike

  10. #23
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Mike:

    The hard start will not lower the initial in-rush. What it does is it gets the compressor running faster, wilch will shorten the duration of the inrush to a shorter time. This may help.

    What is interesting in your latest comments is that it seems that something is shutting down the unit right away. It could be a controller in the compressor unit (if there is one), or it could be in your electronic thermostat (which you seem to have). What I think is happening is that one of these controllers is resetting, which will set a startup timer of 5 or 10 minutes (short cycle timer). This could be easily due to a voltage dip when the compressor tries to start, causing the controller to detect a power loss and restart the short cycle timer. If the thermostat is the culprit, it is most likely getting its power from a 24 volt control transformer in the air handler. If this is the case, it could be a voltage drop at the air handler, due to low incoming line combined with additional voltage drop at the air handler as the blower motor tries to start.

    You could try a non-electronic thermostat as a test to see if it is the electronic thermostat. Solutions to this problem may be as simple as increasing the wire size to the compressor unit or air handler or both. Again trying to get voltage dip readings will point you in the right direction.

    paul

  11. #24
    Join Date
    Jun 2004
    Location
    Clayton,NC
    Posts
    407
    Also don't forget that you will have a different control voltage going from 208 to 240. You must change the tranformer wiring. You may not have enough voltage to pull the contactors in.

  12. #25
    Join Date
    Jun 2005
    Posts
    28
    stevehvac,

    The unit was originally set up to run on 240, then I switched my set-up to 208 and it ran fine. Then switiched back to 240 and it ran fine. So, nothing was changed. I was told by electrical contractor that most modern motors designed for 240 single phase ran fine at 208 single phase.

    Mike

  13. #26
    Join Date
    Jun 2004
    Location
    Clayton,NC
    Posts
    407
    If it ran fine then it is a non issue but the eletrical guy is wrong on it makes no differance. It might not matter to the motors but the transformer could give you problems. If it is running on 240 volts and is setup that way then the transformer has the copper going around hundreds of times until it's reduced to 24 volts of control voltage. Now what happens when you have only 208 volts going into the tranformer? Ive found that you may get 22 volts going out. Then after running the t-stat and fan you have 20 volts. Then when trying to run the compressor you have 18 volt which isn't enough to pull the contactor in all the way.Once again it may be a non issue but switching the voltage can have an effect on the control power you have.

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