Strange Thermostat problem...please help.


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Old 08-13-11, 10:42 PM
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Strange Thermostat problem...please help.

I have two central AC units in my house. They are Heil's highefficiency 5000 series and they work okay. The problem is that when one unit is running, the other one's compressor is also running. If the downstairs AC outside unit is running, then the compressor for the upstairs unit is also running (not the outside fan, just the comprressor). Same thing for the upstairs unit. Seems like the thermostat wiring must be done wrong, but I can't find any place where the thermostat wires intermingle between the two systems. Any ideas?
 
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Old 08-14-11, 01:30 AM
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better find out real quick especially on that condenser running without the fan if you don't have a HI Pressure safty your going to burn that compressor out...constantly tripping the internal.test this...pull the stat off the subase on one then run the other see what happens and then reverse the removed stat.do you have a transformer in each airhandler/furnace are the units located next to each other inside the house.
 
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Old 08-14-11, 06:38 AM
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Are you saying to disconnect one of the thermostats and then test the other one? Or are you saying to disconnect the contactor in the other outside unit? (Could do that and check for voltage) Here's more info: These are two systems, one upstairs and one down, same size units. Thermostats are located one downstairs and one up. Airhandlers are six feet apart in the attic and outside units are five feet apart outside. I actually noticed this a couple days ago and thought it was just a stuck contactor on one of the outsdie units (so, already replaced contactor on the downstairs system). After testing everything, I noticed this other problem. I traced thermostat lines up in the attic to make sure there is no cross connection of thermostats between the air handlers. Now I am going back up in attic to trace thermostat lines completely. Maybe the two termostats share one 24v transformer and there is some voltage bleed that is actuating the other compressor. The thing that is so weird is that the contactor diagram in the schematic shows that there is one actuating coil, which would mean that, if there was some errant voltage being applied to the contactor, it should turn on the compressor AND the the fan. The fan never turns on. Also, this works both ways: Downstairs turns on upstairs compressor and upstairs turns on downstairs compressor. I will post again after I completely trace the thermostat lines and do the disconnect test that you suggested. Thank you for your comment!
 
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Old 08-17-11, 03:54 PM
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you just solved your problem the air handlers have the control transformers and with the they are doubled over thru the stas calling in the wrong comp/condenser fan..so it is all one trans former basically....then that means the upstairs air handler is controlled by the down stairs stat and visa versa...you need to trace the wires from each condenser and verify they go to the correct air handler then verify the air handler goes to the right stat if you see a tranformer in each air handler they should be totally seperate surprised you haven't burst a transformer out with them both stacked controlling 4 total items....can you use a meter and ohm out stuff..at least an audible ring out will verify which is which...do all testing with all power off outside and inside.if you pop the stat off the subbase the easiest test is disconnect R and Y go out to the 2 condensers disconnect the pair of low voltage wires going into each condenser....put meter to audible/ohms..and have somebody touch/retouch the wires inside at the subbase check each condenser pair when you see or hear something..thats the condenser for that stat....do the same with the air handler touching R to G and check each air handler....i'm exhausted...hope you have a meter your right on about the compressor runs but no fan thats the next mystery it is ONE contactor calling in both..lets hear back
 
 

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