How to wire a/c thermostat

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Old 07-06-20, 10:51 PM
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How to wire a/c thermostat


How to wire from duo therm thermostat to Honeywell lyric t5 thermostat thx Gigi
 
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Old 07-07-20, 05:37 AM
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I just did research on thermostat you have, and looks like that is RV thermostat using 7.5V DC instead of standard 24V AC used in HVAC.

Honeywell Lyrics T5 requires 24V AC. So the short answer is, you cannot install Honeywell thermostat.

You will have to use battery operated thermostat or keep 7.5V thermostat. If you can find a way to supply 24V AC to thermostat, that will work as well, but not sure how RV AC system is wired. It probably won't be easy since everything will be DC and lower voltage than 24V.
 
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Old 07-07-20, 11:28 AM
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Welcome to the forums.

You can use a battery thermostat to replace the DuoTherm one. One big problem is that you have stranded wiring and that can be hard to get into small terminals.

The wiring is as follows.

Blue and brown ---------> G
Yellow ----------------------> Y
White -----------------------> W
Green ----------------------> R
Tape off the red wire.
 
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Old 07-07-20, 11:56 AM
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This is relays Iím using for 12v 1 onside 24v otherside I have 24v transformer installed & thermostat got 24v power from transformer all Iím going to use for AC where should I put hi fan wire & green wire Iím not using furnace heat only cold side any help will appreciate thx Gigi
 
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Old 07-07-20, 08:09 PM
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How is your 24V transformer wired?

Thermostat is basically bunch of relays.

Supply 24V AC between R (Jump Rh and Rc of both are present) and C terminal of thermostat.
Also, connect wire from C terminal to A1 of 3 relays.
Then wire connect of W (Heat), Y (AC), G (Fan) wires to A2 terminal of each relays.

Connect 7.5V wire from your existing thermostat to COM terminal of each relays.
Connect Cool wire to NO terminal of relay connected to Y.
Connect Fur wire to NO terminal of relay connected to W
Connect Fan wire to NO terminal of relay connected to G

According to my research, there is Hi Fan and regular fan speed for RV AC unit. Residential thermostat does not have 2 speed fan control. So, you will have to install a toggle switch to switch between Fan and Hi Fan if you desire. Otherwise, you will have to just stick with one speed.
 
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Old 07-07-20, 08:18 PM
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@ lambition.

You need to be careful with these systems. The 7.5v line is only used to power the thermostat. When replacing the stat.... the red wire is not used. The functions switch to ground..... not 7.5v.

My wiring illustrates using a battery powered stat.

The OP doesn't need to control the heat.
If there are two relays available..... one should be used for A/C and the other for fan.
The thermostat will get 24vAC and that will be used to control the relays.

Input of one relay to C and Y.
Output of that relay should be common to green and NO to yellow.

Input of second relay to C and G.
Output of that relay should be commom to green and NO to I believe both blue and brown.
You can also try just blue or brown to see what the fan does.
Brown only may be low speed while blue only may be high speed.
 
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Old 07-08-20, 04:50 AM
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I didn't know that RV thermostats pulls to GND.

In that case,
Connect GND wire from your existing thermostat to COM terminal of each relays.

However, this video tells me otherwise..
https://www.youtube.com/watch?time_c...&v=fzH3vTZe3Qc

Although OP said he doesn't need heat, since he has 3 relays in the picture and wiring is there. Why not keep it connected.
 
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Old 07-08-20, 09:57 AM
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The unit in the video is a Coleman. The OP has a DuoTherm system.
 
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