I have a 12v supply at the A/C roof opening. I'm replacing an old Coleman A/C. The new control box, which has to be mounted somewhere in the roof opening, has 3 12v wires coming out labeled as following. +12v from supply, +12v to t-stat, -12v from supply and to t-stat. The t-stAT will be wall mounted close to a 12V supply, So why do I have to run the t-stat 12V supply clear from the roof opening? Dometic doesn't have a clue!! They are virtually worthless in their responses!!
Ok let me think a little about this, the reason the control box has wires to connect to the thermostat is because some how the power has to run through the thermostat so it can be controlled by it. as you know the thermostat is nothing more than a switch that gets activated by temperature. now lets figure this out. you say the box has only 3 wires, but in your description you mentioned 4. how many is in total?
Testimonial: "Yes, the t-stat has 3 connections. Plus & Neg 12v & one "comm" wire. I assume comm is communication. The control box has 6 wires coming out. 2 are dedicated furnace wires. No worries there. One wire is red/wh & is labled +12V to T-stat. Another solid red wire is labeled +12V from supply. Black wire is labeled -12V from supply and to t-stat. One orange wire labeled comm to t-stat. These wires all come out the back of the control box which will be mounted in the roof opening. I do have 12V supply at this opening. 120AC also."
ok, you are right the wires labeled +12 and -12 to termostat, are to operate (power up) termostat.you can eliminate the +12, but the one labeled -12 to supply have to connect to negative. the common would be to trigger on/off, connect the two labeled common together.
just connect your t-stat to your wall supply, and the only wire that you will have to run up will be the common
remember; you are responsible to judge and act acordingly after getting advise from an nuknown surce. best luck to you!
It just makes no sense. Why do they put +12 into the box & then send it back out again to the t-stat? The one neg from the box just gets tied to the neg supply outside the box & to the t-stat.
ie: Why does the +12v suppy to the t-stat first have to go through the control box?
maybe so it can be controlled by the same breaker
or maybe in case the unit is installed on a non-suitable rv with no t-stat power supply
something else i just thougt of that would be unprobable is that the t-stat uses a lower amp current and the main unit regulates it.
There must be a reason to supply the +12V to the t-stat from the control box and not from just any +12V source. I'm going to do it their way but use a close by -12V source at the t-stat. That will save me one wire from the opening for tying in the 2 furnace wires. That +12V out of the control box must be serving a dual purpose at the t-stat. Anyway, thanks again for your input.
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SOURCE: I have a coleman evcon
The most common wiring is: This sometimes varies as to installers preferance.
Red wire is your supply power to the T-stat. R terminal
Green wire is the blower fan. G terminal
Yellow wire is compressor contactor Y terminal
older units used a blue wire to Y
White wire is heat auxilary or black wire W terminal
Orange wire is reversing valve O terminal
Blue wire is the common C terminal
Black wire can be emergency heat E terminal
Best thing to do is replace wire for wire from t-stat to t-stat
or write down the colors to which terminal on the old t-stat and match to the new. make sure you SECURE POWER to the Air Handler, furnace and condenser before replacing any t-stat.
It is very easy to short the wires out if the power is left on and take out your A/H low voltage fuse or transformer.
SOURCE: keston c40 honeywel 9400c programmer
do a s plan plus and buy a poly plumb roomstat combined programer with built in relays as you require the relays to stop back feed! simple!
SOURCE: analog thermo.stat control kit
Have you tried removing the RH wire connected to the thermostat and try it ? This might rule out furnace as short in system. If it does the same, put RH- (heat) back on and try removing RC-(cool) , if it doesn't pop the fuse, you may have isolated the problem.?
SOURCE: I replaced an old mercury
Did you shut the power off to the air handler/furnace...... before you installed the new thermostat??? You may have shorted out the transformer or blown the transformer fuse...... If you try to put the Fan switch on the stat to Fan ON does the fan come on ..... if it does the transformer is OK.. On the new thermostat did you program it to tell it that you had a heat pump system ???? Looks like you had it wired right. Here is a pdf manual for a RTH6350 http://customer.honeywell.com/techlit/pdf/PackedLit/69-2416ES.pdf
Its on page 13 Advance setup for tell the new stat that you have a heat pump....There is also a Honey well Hot line on page 2 Hope this helps.
SOURCE: Replacing an ST699 with a
Disregard wire colors. Instead wire by terminal designation. In other words :
Wire on "R" Terminal on old thermostat to "R" Terminal on new thermostat no matter the color.
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