Question about Honeywell Programmable Thermostat Heater

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Honeywell RTH230B a/c problem

We bought this thermostat late last year and worked fine through the winter and worked fine up until now. Was keeping the house at any temp we wanted (we like it cool so its usually set at 68-70). Now no matter what you set it at, it stays at 72-73 on the thermostat. Thought maybe the battery was bad, changed those.. no help. New filter.. tried that, no help. The air is actually coming on and feels cold but wont get to any lower than 72 on the thermostat and it's really warm with the 100 degree Memphis weather and humidity. This goes for manually changing the temp or setting the auto program. If this is a thermostat problem, any help would be appreciated, if it sounds more like a unit problem, I'll have to call someone! Either way your advice is appreciated!

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If you set the thermostat on 70 and your house won't get ant cooler than 72, there is a problem with your system,not your stat. I'm thinking you are low on refrigerant if it is somewhat working. when the unit is running, if you can get your hand on the larger refrigerant line under the black insulation, it should be cold, about 55 degrees.

Posted on Jun 19, 2009


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Switched from manual to Honeywell rth230b. It was working fine until yesterday. We had it since last June. AC worked all last summer and Heating during winter. The AC was working this year too until...

I will assume this is a central air conditioning system. From what you tell us about the symptoms a few things come to mind for you to check.

1. Change your thermostat and see if that cures your problem.
*The following steps requires the use of a multimeter and work around electricity, use due caution or call a professional.*
2. Check the contactor inside the outside unit while you have the thermostat calling for cool and see if it is pulled in or if it is stuck. If you are not comfortable around high amp electricity then please call a professional in your area to make these checks.
3. Check to see if the thermostat wires going to the outside unit are sending 24 to 28 volts to the unit. This will tell you if the problem is outside or inside the home. If there is no voltage there then check at your furnace to see if the t-stat is sending the power on the Y connection.

There is much more to check but this should get you going in the right direction and will locate the problem in most cases.
Hope this helps.

Jun 14, 2011 | Heating & Cooling

1 Answer

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you will have to reprogram it according to the operating manual.
The manual is available on

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for starts, check fuses in disconnect box by condensing unit

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Do you have a heat pump? If so, not compatible. What i did was move the jumper on the thermostat (RH RE). This is on the inside of the thermostat - NOT the red jumper!!! and got the AC working (the heat had already worked during the winter, problem only became apparent when I needed to use AC). I may have to change the jumper again when the season changes...not sure yet.

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THIS TYPE has been deemed defective! changeout to a different type.

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Sounds like a relay sticking. Possibly in the thermostat or possibly the furnace relay at the furnace. The next time it happens, unplug the thermostat from the wall. If the furnace still runs then it's the furnace relay.

Hope that helps...


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I can't program my thermstat

go to There you will find a search tab. Type in the exact model number of your thermostat. You will be able to download the installation/owners manual.

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