AC Split unit not working


  #1  
Old 06-18-08, 07:45 PM
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AC Split unit not working

I had the outside unit replaced 4 years ago with a Luxair HBBC-F0485G 4 ton 12 seer unit, about a month ago the had to replace the condensor unit fan today when I got home inside and outside unit would not operate checked both breakers and were not tripped, turned inside unit off of auto (at the unit not the thermostat) to run and blower came on but no response from compressor unit. Had to engage contacts at compressor and both fan and compressor turn on but will not stay running if contactors are released.

Any suggestions? I did not find any reset buttons or fuses to check. I did look on the compressor and followed all wiring at the compressor unit and verified that there were no fuses or trip relays.
 
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Old 06-18-08, 08:07 PM
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The contactor may be bad. Do you have a volt meter? If so, when it's supposed to be on, you should have 24-28 volts or so at the coil (not the high voltage, the smaller wires going to it. If you have the correct voltage, the contactor is bad. Make sure to give it 5 minutes or so since many thermostats have a built-in delay (if you know it doesn't, then ignore that). If you're going to replace the contactor, make sure to have power off to the condenser unit AND the indoor furnace or AHU.

If you don't have power there, the problem is either the thermostat or the wiring between it and the unit, but check that first. Is it a zoned system?
 
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Old 06-19-08, 06:26 AM
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This is not a zoned unit to answer your question. But I have tried to bybass the thermostat by jumping the H to RC at the thermo and also tried jumping the H to R ( at inside unit to verify that the wiring between thermo and inside unit not damaged) with no luck, I will have to purchase a new volt meter this evening to check the 24V at the contactor unless there is another way to check the low voltage to the contactor.

I'am pretty confident the problem lies in the contactor or the low voltage to the contactor but was trying to verify this with someone who has more knowledge of the A/C workings in case there was a simple solution I have overlooked.
 
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Old 06-19-08, 07:19 AM
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Air Conditioning Repair

i don't think i have seen a thermostat with an h terminal y is always been the terminal to call for the outside unit to operate but anyway because your fan is coming on when you put it in the on position you know you have control voltage so if you can determine which wire going to your outdoor unit crries control voltage to that contactor and which is the common get those two wires 24v and your condensor comes on that will eliminate the wiring from the air handler to the condensor then hook those wires up as they were and move to the wiring from the air handler to the thermostat if they are good then it is your stat if the condensor never comes on at the first step then you will probably need a meter because you could replace the contactor and not realize that a safety was open such as a high or low refrigerant pressure switch as a matter of fact before you do anything would be looking for a manual reset high pressure safety somewhere on the outdoor unit i am not sure where it would be on a luxaire but if you have the wiring diagram on the inside of the control box cover it will tell you if you have one
 
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Old 06-19-08, 10:54 AM
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You are correct Iit is Y , not H as I originally stated.
I wanted to know if the 24V system at the compressor unit could be bypassed. It appears that the answer is yes ( if I read your reply correctly)by jumping the blue (low voltage wires) from one side to the other of the contactor.

Is this correct?

If this is correct and I jump the contact and compressor starts the wiring from the handler to the compressor is faulty?

If the compressor does not start the problem would be anything from the contactor to the compressor?
 
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Old 06-19-08, 01:45 PM
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Normally, there's no transformer in the outdoor unit. It's in the AHU. R comes from the transformer down to R on the stat. It closes to Y on call for cool, and Y goes to one side of the contactor coil outside. The other side of the coil goes back to C on the trans. terminal board. If you jump the cont. coil while the stat is calling for cooling, you'll burn out the transformer. Just put a meter on the cont. coil & chk for 24v. If there is, then you've a bad coil (sometimes you can buy the coil seperate)
No 24v? Then check for manual resets on pressure switches, usually mounted on the piping. HPCO tripped, clean the cond. coil. LPCO tripped, low on refrigerant - Call for service.
Tom
 
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Old 06-19-08, 08:35 PM
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Air Conditioning Repair

You can't jump across the contactor coil if there is no voltage nothing will happen and if there is you will either blow a control voltage fuse or burn up your transformer the only jumping you can do is over switches not over loads.
Switches are thermostats, relay contacts or safeties. loads are contactor or relay coils or motors. Without a meter you are definitely guessing but the advice I gave you will let you eliminate some possibilities and more narrowly define the problem, electricity is like a river you can dam it up and stop it, redirect it or let it flow and do it's work. Switches allow you to do this and the wiring is the path that takes it to the switches if I could draw on this forum I could show you but any wiring diagram you could find (and your unit has one) will show you that out of the transformer is a supply side R and a return side C if you get the R side to one side of a load (contactor, relay coil, etc) and C to the other side and nothing happens then the device is bad that is why I told you if you have two wires going to your outdoor unit and you tie one wire to each side of your transformer then you have effectively eliminated half your possible problems (thermostat and control wiring to stat) leaving only the wiring from your air handler to your outdoor unit and the outdoor unit itself as potential problems but if you had a meter you would be able to put your leads on each side of the coil terminals on your contactor these terminals are not the larger wires on the main lugs but the smaller wires on the side. If you don't get 24v on the coil and you know you are providing 24v to the wiring to the outdoor unit then you need to check first for an open safety (high pressure manual reset or low pressure out of refrigerant) if no open safeties then check for 24v at the wiring coming into the outdoor unit no 24v then you have a broken wire between your air handler and your outdoor unit
 
 

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