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AC question

This is a better Schematic


  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    I was trying to draw a schematic for my control system to post but I am the computer idiot. My question was how to hook up the "fan only" lead to my system. I thought it would go to the air handlers 24V contactor connection. but the red stat lead is there now. If I replace the red with green That will turn on the air handler all right but my compressor is atteched to a set of contacts on the airhandlers contactor. So if it runs the AH it will also Run the Compressor. The lead from the compressor is a switch lead from the compressors contactor it has its own 24V source. So I don't want to feed the 24v from the wall stat/Air handler up to the compressor???? I am missing somthing. My instructions with the stat make it sound like the compressor should signal the air handler to start after the "cool down delay". Sorry I have had no luck finding old Singer lit. Singer mod# C080a0 Ser# 550001-19-0005 to know if this system has such a delay? It is working and we are cool It may be better to leave it alone. The fan only would be nice for the Fall. Thanks for any old info you might know of. T
  • Jon_10
    Jon_10 Member Posts: 47

    It would be nice if you could post a legible picture of the wiring diagram for the A/H and Condensating unit and thermostat. Sounds like you have 2 24 VAC power supplies, one on the condesating unit and one on the A/H. You are headed in the right direction but you are not familar with low voltage wiring schemes. Are either of the units run on three phase primary power? That brings up another problem. Post the pictures of the three wirinig diagrams and it will be simple to fix. All so let us know if either or both units run on single phase or three phase. The information you gave is not enough to safely diagnoise the problem. From what you said above "the compressor contactor is all so connected to the A/H contactor so when the A/H runs the A/C condenser runs" The wiring on both the A/H & A/C has been changed at some point. With-out the wiring diagrams it would be hard with your limited knowledge to instruct you in correcting the problem. I think you have reached the limit of your wiring expertise and now in order to correctly and safely corrrect this problem it is time for you to spend a nickel and get a tech. This problem you have is a simple fix for a technican for he has the knowledge and tools to rewire the unit. I instucted you on the Honeywell damper motor and it's wiring on an earlier post, you demonstrated no knowledge of controls then and again you are doing the same. If you want it running correctly and safely, hire a tech.
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    Here is how the system is wired at this time.
  • soot_seeker_4
    soot_seeker_4 Member Posts: 22

    how do you have time to sell furniture & keep playing with your a/c wiring?

    i like your picture - however, as you can see, people are gonna keep yelling at you for the sake of your own safety. i would say this though. are you *sure* you have 3 phase (460v 3ph?) power feeding that unit? i believe it's illegal to wire 3-phase power thru a 2 pole contactor. you're showing one leg of the compressor (and the AH) wired directly. other than some dangerous old method of providing crankcase heat to the compressor (thru one leg & some case ground strap - bad idea - i heard of 2 legs but not 1) i really can't fathom why anybody would wire it like that. [if you see 2 of those legs coming off the main conn. *prior* to the contactor & wired to a crankcase heater band around the base of the compressor then they're certainly not generating cc heat from the legs.] strangely, the way you have it drawn it would basically be wired ok for single phase 208-240v with the direct wire to the compressor & the AH being the neutral. are you sure you're not running that? there should be some metal tags on the unit that will tell you or take a look at the AH motor and see what the voltage & phase specs are on the label.

    getting back to the matter, if you just wanted to run the fan w/o the compressor, why not just slide the thermostat on & turn the compressor cut-off off? that *would* do it. if you wanted to get fancy you could add a 24v relay off the fan motor switch that would open the 24v to the compressor contactor at the t-stat cut-off box & have it wired without even going on the roof. no?

    and don't burn the building down.


  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845
    Looking at your diagram...

    you will need to add a relay due to the fact that your condenser has a separate 24 volt source. You wire a normally open relay into the 24 volt circuit going to the condensing unit, connect the "Y" terminal on your thermostat to one side of the coil on the new relay, and the common side of the AH transformer to the other side of the coil. Then you make sure the hot side of the 24 volt AH transformer (red) is hooked to the "RC" terminal on the t-stat, and the green wire is hooked to "G" on the t-stat, and the AH contactor. Then when you call for fan only, the AH contactor will energize the fan, but since there is no "Y" (cooling) signal at the new relay, there will be no 24 volts going to the rooftop condenser.

    This, as I see it is the simplest way to achieve what you desire.
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398

    Sorry I made an assumption on the High voltage. This part works and has not been messed with. I know that the stamp on the roof top compressor is 3 phase I have not looked at the contactor inside of that unit. I was told by the last tech that was out, that the unit had a contactor inside and its own 24V supply. It kicks on when the leads are closed so I believe he is right. The AH contactor is not labled and it may be running 220V single phase I dont know but there are only 2 large High voltage wires being switched inside of the AH contactor. Sorry for the mis-information. The 24V system is what I had to re-assemble Thanks for all of the advice and I will try the relay trick. I guess that the fan only was not hooked up before. Thanks T
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