adjust thermostat sensitivity?

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adjust thermostat sensitivity?

Postby June » Wed Jul 09, 2008 9:50 am

My old Coleman furnace/AC seems to be working fine, but the thermostat doesn't call for the AC until the house temp is much higher than the setting. I keep it set on ~77-78 F; it kicks in at mid to upper 80's. If I lower the setting the house gets uncomfortably cold before it shuts off. Is this normal, or can I adjust the sensitivity, or do I need a new thermostat?
Evcon 025-35368-000 type 1C20-29
June
 

Postby tnt17 » Wed Jul 09, 2008 12:28 pm

Any chance of your floor registers are close enough to effect the thermostat? Like a/c flow within 4 to 5 feet, or the opposite? I have a similar problem, switched to a digital thermostat, but still at night it gets a tad cold. but i was happy that at least my readout on the thermostat would show 73 and the setting was 73, so thus it was kicking on.
Just for kicks, i put 2 wireless weather stations, one in the living room(50 feet from thermostat) and one in the master br(other side of house). The closer one in living room shows a readout of indoor temp at 75, bedroom shows 73. It seems the thermostat area is a degree difference then living room at most times and the master br a couple degrees cooler. I blame the open space/cathedral ceilings for the warmer living room area.
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RE: adjust thermostat sensitivity?

Postby Robert » Wed Jul 09, 2008 1:59 pm

Hi June,


They can be calibrated, but best solution is to replace.

I would go with a Honeywell digital or a White Rodgers digital.


Honeywell can be bought about anywhere. WR have to be bought at HVAC Supply.


Take care and best wishes,
Robert
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RE: adjust thermostat sensitivity?

Postby June » Wed Jul 09, 2008 2:10 pm

Thank you both for input. ...think I'll get a new one, which leads to another question. I believe the 2-wire thermostats are installed when there is just heat, no AC. My AC was an add-on sometime before I bought the house. Is re-working for a 4-wire something I might be able to do myself?
June
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RE: adjust thermostat sensitivity?

Postby Robert » Wed Jul 09, 2008 2:55 pm

Hi June,

2 wire t-stats work with a/c also if there is a 2 wire a/c control box or the components from one are installed.


For a 4 wire t-stat, you will need a 4 wire a/c control box or the components needed from one.


Are you currently using a 2 wire t-stat ?



If so, do you have an a/c control box with two rocker type switches on front of it for heat-off-cool and fan-auto-on ?



Thanks,
Robert
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RE: adjust thermostat sensitivity?

Postby June » Wed Jul 09, 2008 3:19 pm

Yes, two wire. I have a box mounted up on the blower housing. It has a rocker switch,simply heat and cool options. Out of the end of that box go two wiring harnesses, one to the blower motor, one down to a box with an on/off rocker switch, a label on top that says 7900 standing pilot series, and from the front of the top box the come 4 wires. The red and white ones go into the wall cavity beside the furnace, presumably, from there to the thermostat. The green and yellow wires connect to a two-wire line that goes through a hole in the floor, to the compressor outside.
June
 

RE: adjust thermostat sensitivity?

Postby June » Wed Jul 09, 2008 3:24 pm

When I went to put the cover back on the HVAC unit, I noticed that the sticker on the blower housing says 2-wire control box 892103. I presume that means I'm limited to a 2-wire thermostat.
Thanks!
June
 

RE: adjust thermostat sensitivity?

Postby Robert » Wed Jul 09, 2008 5:56 pm

Hi June,

You could switch to 4 wire, but without my being there to see exactly how all is wired, would not be easy to explain the wiring changes necessary.


I would advise a Tech for that.


The two wire t-stats work fine, you just have to set for heat or cool at control box instead of t-stat.


Also, IF the 2 wire t-stat has a heat-off-cool switch on it, be sure it stays always set to heat, even in cooling season.


Your a/c is controlled by the control box reversing relay inside.


Does your 2 wire control box have a wiring diagram on the box or cover ?




Take care and best wishes,
Robert
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