Coleman Presidential III Thermostat Wiring

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Coleman Presidential III Thermostat Wiring

Postby justplumducky » Mon May 31, 2010 1:17 pm

Coleman Presidential III LP Gas Furnace
Intertherm A/C unit (split system)
Furnace Model No: 7956-856
Serial No: 058774442

Is this furnace supposed to work with only two wires connected to the thermostat? Only 18/2 connected to stat, and I have to turn the main On/Off switch (at furnace) to ON to get it to run for Heat or Cool, while also using the HEAT/COOL rocker switch on the right side of upper control box, with the left side rocker (CONT/AUTO) set to AUTO.

Thermostat is Honeywell digital with jumper between Rh & Rc, red wire is attached to Rh, white wire is attached to W .

Dont know if this helps, but have a pic (can get more if needed):

Image

The small transformer you see on top of the control box belongs in the box below, that covers the 120v connections to the main ON/OFF switch and goes out to that transformer and a couple of fan (limit?) switches on the right side of that box. That transformer has no continuity between the load side terminals and was getting ready to replace it, when I discovered that the A/C would still work - it's getting voltage from the transformer in the upper control box (pictured).

There is one set of 18/2 feeding the wall thermostat and another set feeding the contactor on the outdoor A/C unit. Yellow and gray ( I believe) feed the contactor.

Does Coleman provide manuals/wiring diagrams? Thx much for any help.
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Mon May 31, 2010 11:18 pm

Hi,

Yes, that is correct for a 2 wire system set up. IF your t-stat or a future t-stat ever has a heat-off-cool switch on the t-stat, always keep it set to Heat at all times.


Then, set your furnace switches as you stated.


We have the manuals and wiring diagrams for sale in our store.

Please call 605 - 229 - 2627 to order one if interested.



Thanks,
Robert
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Re: Coleman Presidential III Thermostat Wiring

Postby justplumducky » Tue Jun 01, 2010 6:19 am

Thanks for the prompt reply.

If I added more wires to the thermostat, could the Heat & Cool functions then be controlled at the thermostat? My digital stat does have Heat/Cool and Fan On/Auto, and two only buttons for setting temp, no other controls on the thermostat.
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Tue Jun 01, 2010 6:51 pm

Hi,


You would also have to replace the 2 wire a/c control box with a 4 wire a/c control box.


Or, have someone experienced in the wiring to know what wires to remove, reroute and what component(s) to add and which ones to disconnect.


Easier to just replace the box, but it is more pricey that way.



Let me know if interested in that and I will give ordering info for the control box.



Thanks,
Robert
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Re: Coleman Presidential III Thermostat Wiring

Postby justplumducky » Thu Jun 03, 2010 10:02 am

I would be interested in the price for the upper control panel, but I've neglected to tell you that my AC is not shutting off automatically.

I also thought I'd better replace the lower thermostat (secondary has no continuity), and replace the thermostat, to eliminate those possibilities, then see if it shuts off, or not, automatically.

Will be doing that this weekend, if not sooner, then get back to unless you have any further instructions in the mean time.

Thank you Robert.
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Fri Jun 04, 2010 12:48 am

Hi,

4-wire A/C Control Box # 7900A6041 can be seen and ordered here by scrolling down to it:

http://www.aberdeenhomerepair.com/store ... esults.php

On a 2 wire system, that would usually be either a bad t-stat or a bad t-stat reversing relay in the a/c control box.


Measure across t-stat wires and see if it reads 0vac or 24vac .


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Robert
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Re: Coleman Presidential III Thermostat Wiring

Postby justplumducky » Sat Jun 05, 2010 3:46 pm

I installed the new transformer for the lower box and measured across the load side and the thermostat wires (red & white) and got a little more than 24vac. Also checked the upper transformer in the AC control box and got 24vac.

I neglected to measure at the thermostat, but I did put a new thermostat on - it didn't make any difference. Cooling and Heating) has to be turned on at the furnace with the main 120v On/Off switch, and shutoff the same way. Put t-stat switch in Heat and Auto like you said.

I'll check for 24vac at the the thermostat in case I got a bad one, but assuming I didn't for now, I'm not hearing any clicks at the furnace when I move the Heat/Cool switch at the t-stat (nothing when moving the fan switch to On, either). Should be hearing clicks (when turning on and off, yes?) from that relay you're talking about (t-stat reversing relay in the AC control box, right?. Not a sound at any time.

The only thing that looks like it could qualify as a relay in that box is immediately to the left of the transformer
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Sat Jun 05, 2010 9:20 pm

Hi,

When you read the 24vac + across t-stat Red and White wires, is it at the time that the a/c "should" be cutting off but is not.


When a/c should be running, you should read 24vac.

When a/c should be off and t-stat satisfied, you should read 0vac.

The t-stat reversing relay is the sequencer to right of transformer it appears.

To left should be the fan relay.



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Robert
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Re: Coleman Presidential III Thermostat Wiring

Postby justplumducky » Thu Jun 10, 2010 7:53 pm

My apologies for the delay.

Yes, it reads a little over 24vac on both the thermostat wires (red & white) and also the yellow and gray wires going to the contactor outside, when the t-stat is off, and regardless of Heat or Cool position at the rocker switch on right side of upper control panel.

Thanks for correcting me on the sequencer and fan relay positions.
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Fri Jun 11, 2010 12:26 am

At the time that the a/c should shut off, you should begin reading 0vac across the red and white t-stat wires.


IF it continues to read 24vac and a/c keeps running past set temp on t-stat, then the t-stat is bad.



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Re: Coleman Presidential III Thermostat Wiring

Postby justplumducky » Sat Jun 12, 2010 11:19 pm

I went out and got a new t-stat (same as the one they were using: Honeywell digital) and it didn't help.

Then I stumbled onto a Coleman distributor here in town who told me, for exact reasons unknown, the Honeywell digital t-stat I was using, with ON/OFF Fan switch & Heat/Cool position switch, bleeds voltage to those control circuits somehow when it shouldn't. He recommended a two wire only t-stat with No switches, or a Heat Only t-stat with On/OFF if possible, because this ancient (or unique....or both?) Pres III model was intended to do all the switching at the control box located on the furnace. He said it should be a simple, snap action-type switching t-stat.

My understanding of "snap action" according to the Coleman Distributor, was "simple On/OFF action of the the bi-metal coil extension that snaps between the On/Off positions as set point temp is reach and/or temp adjustment lever is moved.

And if I couldn't find one of those (above), then a non-digital, mechanical switching t-stat (snap action) with the Heat/Cool and Fan position switches, and leave it in the Heat position year-round, which is what you said previously.

You agree?
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Sun Jun 13, 2010 12:37 am

Yes. With a 2 wire system, as the a/c cools and lowers the temp, when it gets to temp setting, the t-stat in heat mode will "think" home needs heat and close.

The signal will go to furnace to turn on heat and will energize reversing relay coil, that opens a/c circuit and turns off a/c and then goes on to give heat.

However, because system switch at Furnace is set to COOL, when signal gets to that point it is dead and you have no heat and no a/c, so unit is off.


Clear as mud, LOL ?

Then home starts to warm up to temp setting on t-stat and t-stat "thinks" it is satisfied and opens which kills energizing of reversing relay coil and closes a/c circuit and a/c comes back on.


Then the cycle repeats itself.

I do not think your t-stat is closing when needed to turn off a/c circuit.

IF it is, then the reversing relay is most likely at fault.


Thanks,
Robert
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Re: Coleman Presidential III Thermostat Wiring

Postby justplumducky » Tue Jun 15, 2010 2:31 pm

Robert wrote:Clear as mud, LOL ?

I do not think your t-stat is closing when needed to turn off a/c circuit.


Well, maybe if I read it a second time :roll:

Right you are, of course... I put a simple, mechanical, heat only thermostat on - it's doing its thing now, properly.

Thank you sooo much !!
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Re: Coleman Presidential III Thermostat Wiring

Postby Robert » Tue Jun 15, 2010 3:36 pm

You are very welcome, happy to help.



Take care and best wishes,
Robert
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