Thermostat upgrade help

My Dometic single zone conversion works quite well actually.

My concerns about the Dometic single zone digital tstat and control system continue to grow. I'd never switch to this from something else. We had the complete control replaced just short of 3 weeks ago. Today I've seen as much as 8 degrees difference on the tstat before the AC kicked on when running in auto. Then it would kick off with still 3 degrees of difference. It will not run on low fan--as soon as the compressor cycles off, then the fan shuts off also. The ONLY way this thing works right is in high fan mode where the fan roars at full speed and the compressor cycles on and off. The temperature control doing it that way is actually close. In addition, Dometic RV products must have the rudest customer service people on earth. I got transferred to the wrong number numerous time, and just plain disconnected once. Rather than spend the $$ on another set of electronics, it's time to mod it like a home system.

Glad to hear it is working :B

Finally, got it all working, with one 'minor' problem. Here in south Texas, we definitely wanted the high speed fan for the AC, which is the Blue wire; the Brown wire is the low speed fan. However, when I put the Blue in the 'G', I had no fan. I could hear it click, but no fan. Putting the Brown in the 'G' gave a low speed fan. I tried many different combinations, including a switch between brown and blue, but this was the only configuration that worked. BRAINSTORM!!!! Why not rewire the control box? I disassembled the box and reversed the high and low speed wires on the terminals on the control board. Now, the Brown Low Speed Wire on the 'G' terminal produces High Speed Fan. Happy Camper.

Minor Problem: Every time that I worked on this, I tripped the breaker and turned the stat off. When I turned everything back on, the stat would put the compressor in protection mode for about 5 minutes before it kicked on. I know the purpose of the protection mode, but if the AC's been off for for 15 - 20 minutes, it should not need protection. Checking further, while it was running, I increased the set temp to 2 degrees above ambient temp, and after about 5 seconds, the AC kicked off. I waited a full 3 minutes and lowered the set temp to 2 degrees below ambient, cool flashed on the display, and it entered compressor protection mode again; this time for only about 2 minutes. Anyone offer an explanation and fix for this minor problem?

clev wrote:
UPDATE

Red not used
Green wire in Rh/Rc jumpered
Yellow and White in Y and W
Brown and Blue both in G

Furnace works good; fan kicks on and in about 1 minute, fire lights

In Cool mode, compressor kick on, but no fan in Auto; fan comes on in ON. Which wire do I need to change?

How long did you wait for AUTO fan? Could the thermostat have a delay? Probably not more than 10 seconds.

Seems odd but try just the low fan with AUTO(orange wire).
Otherwise I am at a loss.

Might get more help if you have the moderator move this to tech issues.

my guess on the fan, you can try putting the TAN (brown? I am color blind) and BLUE wire into the terminal on the thermostat marked "G". Remember my note about the fan, only in AC/ cool mode. Further, Note, there is usually NO low / high speed fan selection on today's home thermostats as furnaces (hence AC units) are typically DC controlled with air volume sensors that are fixed at the board level.

OOPS... I see that is what you have tried.... sorry as I didn't remember all your good info.

OK... then hook the TAN to the cool (yellow, I think) and leave the BLUE on the G.

progress.... :-)
sorry but your "testing" is "all over the map". Normally, one would take measurements, especially voltage with respects to a ground (preferably a KNOWN ground)... in this case, based on my reads of some schematics, ground can either be the black or green.

Anyways, doesn't matter at this point since you got most of it working... its one of those "mysteries of life"...:-)

As you have "found", it appears that the RED is of no value to you (at this time)... based on my read, the red provides power to the "freeze detector" which most home stats don't use.

Your Y and W are what is "controlling" the cool and heat mechanisms. By hooking your G to where the RED would have been, you are providing the needed ground to operate those functions (in the home, they / you would have been sending them 24v). Good, great.

I am still trying figure out the wiring differences for the fan.

NOTE: I think that the only reason you got fan for the furnance is cause that's how the furnace works... there is NO seperate fan control. Once the furnace control is energized, it controls the fan on the unit, NOT the thermostat.

UPDATE

Red not used
Green wire in Rh/Rc jumpered
Yellow and White in Y and W
Brown and Blue both in G

Furnace works good; fan kicks on and in about 1 minute, fire lights

In Cool mode, compressor kick on, but no fan in Auto; fan comes on in ON. Which wire do I need to change?

I decided not to use the kit if I can get the Honeywell to work, so I am using the existing analog control box.

Testing the Tstat wires, not hooked to the Tstat, the red wire gives 7.8 volts using grn as the ground; 0 on all others. Blue as positive gives 11.9 on grn, 3.5 on Y, 0 on others; Y as positive gives 8.9 on grn and -3.5 on others; W as positive gives 11.9 on grn, 3.5 on Y, and 0 on others; using Grn as positive gives -'s on all; using brn as positive gives 11.9 on grn and 0 on others.

So, B and W have 11.9 using grn as a ground and Y has 8.9 using grn. Is it safe to assume that Blue should be used as the trigger wire connected to Rc/Rh?

I "misspoke" about the switching of voltage. The thermostat is actually switch grounds to operate the relays in the control box. The battery in your new thermostat is providing the power to operate the wall thermostat (ie. operation of the display and internal "relays" to switch the grounds from point to point... may not be an actual relay in the thermostat but an IC).

Sorry for the mis-direction.

PS. you are using the old control not the new one that came with the kit... right?