Have an american standard 3 ton roof mount. Heat will not come on if outside temp drops below 45, replaced thermostat, technician can' t find problem. What's going on?

Does it cool when in heat? Is this a heat pump? What's supply air temp vs. return air temp? Outdoor unit running?

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Had error code 91 on Trane XL19i thermostat. Heat season on duel fuel system. Repair tech said board is bad ($963) and transducer ($1000). Unit is 3 ton 12 years old. Does it make sense to repair or put in a new unit?

It may be getting low on refrigerant due to a small leak. I'd have it serviced soon. When running at less than peak efficiency it will much more often switch on the heat strips and they are not cheap to operate.

check thermostat wire to outside unit. replace contactor coil in outside unit.

When was the last time you had the filters changed?

Remove the cover of the circuit board and controls on the outside unit. Some units have a thermostat that allows you to set the temperature at which it switches to the second stage of heat. Set that for about 34 degrees.

I have a honeywell TH8320U thermostat and American standard Air handler with heating unit put in. THE thermostat works fine with the ac and follows the programs I have set. However the heat is a different story. The thermo clicks on to follow program but the unit does not run. (auto settings) If I place the thermo in heat and turn it to on I get heat?

Find a reputable HVAC contractor to do a room by room analysis with heat and cooling loads calculated and units sized and duct requirements and compare to what you have.

The air not being cold is not necessarily an indicator of anything malfunctioning. High efficiency units for instance don't produce cold air.

Since you have had someone look at it, the duct work may be collapsed which restricts air flow or uninsulated which warms up the supply air. Either one is a possibility. Any Cox Cable guys been stompin' around your attic lately? Wouldn't be the first time.

Usually, when the air coming out of the vents is not cold enuf it's because your freon level is low. Probably leaking, but they can usually recharge the freon and it will work for a while. Try another repair company and see if they can recheck the freon level.

We have a high efficiency unit and it produces cold air, so I don't know what previous poster is referring to. Air conditioners are supposed to blow cold air.

Sorry, to tell ya but it is normal if the outdoor temperatures are much below 45 degrees. Below 45 degrees there is little heat outdoors for the heat pump to grab to heat the home so it will run 24/7 and blow cool or cold air. Below 45 the temp of the air coming out the vent will decline and you will get no heat from the heat pump itself as you near freezing.

Your emergency heat or auxiliary heat is electric strip heat. But it only kicks in during normal operation if the temp in the house drops 3 degrees below the setting. (some tstats if can be 5 deg.) Otherwise the heat pump will blow cool or cold air the rest of the time if it is too cold out.

To prevent it from running all the time and blowing cold it is recommended if the temp outside is falling below 45 degrees you should just switch to the emergency heat setting, which shuts the pump outdoors off, and just heat with the electric.

But if there is no heat outside the heat pumps will blow cold. They are the cheapest and most efficient forms of heat but only as long as the outdoor temp is above that 45 deg..

I'm guessing that if you haven't experienced this you live in some place with moderate winter temperatures like in Northern Florida and rarely get very cold winter temps like the freezing you have seen there recently.

It will likely blow much warmer when the outdoor temp rises.

Your outside unit is not defrosting. You need to call a service tech to check it out. Defrost board sensor or low on gas. Also you amy have an outside tstat that is not working correctly. Rus

The Thermostat Wizard is an interactive tool that will guide you through wiring and troubleshooting your thermostat, as well as programming it to the most comfortable settings for you and your family. Simply answer the questions from the Thermostat Wizard to correctly connect, troubleshoot and/or program your Honeywell Thermostat. You can even print the instructions and bring them right to the thermostat to help make things easier.
Go to: http://yourhome.honeywell.com/Consumer/Cultures/en-US/Support/Thermostat+Wizard/

However - the problem is probably not with your thermostat but with your furnace. It is most likely a dirty flame sensor - a maintenance issue. If you have not had your furnace serviced recently (more than 1 year) that is where you should start. Modern furnaces require regular maintenance.


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