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My central ac system occasionally runs too long and the temperature gets way too cold. The digital thermostat reads that the temperature is too high so the ac still runs. This doesn't happen all the time but last night we had the thermostat set on 74 and when my wife got up during the night it was 67 degrees in the house (another thermometer read 67, the thermostat read 78)

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  • Anonymous Mar 25, 2014

    Have a Liebert unit for a data center that is tripping on high head. Suction and Liquid readings are good, and it will run until we hit cold weather (Logs show it usually happens on a cold night) ... Tested electrical and everything is good there as well. Thinking it may be a problem masking an even bigger problem...

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I have seen this is many digital thermostats. The worst problems usually come from the touchscreen thermostats. I would suggest installing a new thermostat. Make sure that you read the instructions before you even remove the old one.

Posted on Jul 03, 2008

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Setting start temperature on central heating thermostat


It sounds like your heating system has to little capacity to heat the home properly. 21 degrees is a reasonable temperature to expect but if the unit is running all the time and can't reach 21 degrees the heater is too small.
As far as setting the thermostat here is a link to the instructions.
http://www.salus-controls.pl/data/product/attach/rt300rf_-_eng.pdf

Nov 22, 2013 | Air Conditioners

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I have a dometic penguin ac rooftop unit. Model no. 630215.421. Fan blows Compressor does not kick on. Fan blows just no cold air. If put on auto and go up or down in temperature On the thermostat The fan...


Bad run capacitor or bad compressor. If you hear an occasional click from the compressor try a new run cap and then a hard start kit. Otherwise it's more economical to purchase a new unit.

Sep 25, 2013 | Dometic Rooftop RV Air Conditioner

1 Answer

I have never used central ac before - how do I set it? If it is on 75 will that cool the house? If I want it cooler, do I put it lower? like 65?


As to your question 'will 75 cool the house?' The answer is 'yes' - if the outside temperature is low enough. Typically speaking you can expect your central AC to cool a properly insulated house to a down to a temperature of about 20-25 degrees lower than the outside temperature. For example - if the outside temp is 95 degrees. You could expect to get your house down to 70-75 degrees. If the outside temp is 110 degrees then you could only expect to get the house to 85 or 90 degrees.

So .. as you can see - your 'inside' temp will be directly affected by the 'outside' temperature.

As to the operation of central air; it is very simple.

I would suggest that you not pay 'too much attention' to what you have the thermostat set on. A comfortable temperature - is a personal thing - so - I would set it somewhere - say 72 and see how I (and others in the house) was handling that setting.

If you want it 'cooler' just 'notch' it down a degree or two - if you need it a little warmer - turn it up a degree or two. Do this "fine adjusting" till you have the temperature setting you are comfortable with.

Usually the more you can leave your thermostat alone the better off you will be from a comfort position and an electrical useage standpoint. Obviously, the higher you have your thermostat set the 'less' it will cost you on your electric bill.

How high you set the temperature is a balance you have to come to based on how comfortable you want to be - matched with how much you want to hold down the electric bill.

hope this helps

Aug 14, 2010 | Honeywell Air Conditioners

2 Answers

My heat unit will not blow hot air unless we go outside and hit a button on the back bottom of the unit. Once we do that it will blow hot air for that cycle. when it is time for it to come on it is cold...


If it does not have a furnace or heating elements for heating, then it is a heat pump, which is rare for a central AC system, but makes sense of the fact that it blows warm air when you reset the pressure switch, which may indicates freon pressure charge problem if your AC system has a reverse valve and uses freon to for heating (heat Pump).

Do you get heating when outside unit runs? if you do, check freon pressure levels and top up to required pressures. The button you depress is a pressure reset switch ... that is if your AC system is a heat pump ... which, as pointed above, it is not common for central ACs.

Nov 07, 2009 | Ruud Central System Air Conditioner

1 Answer

The last time i used my ac here in las vegas nv. was july 2009 and it was freezing. i terned it on to check to see if it still blew cold and it dosnt. blows air fine but dosnt get cold, is there a re-set...


central air or window unit? central systems use a low/high pressure limit switches which self reset when pressures are nominal. suction about 50-60, high pressures around 300.

Oct 20, 2009 | Air Conditioners

1 Answer

When i was fixed a problem in central ac trane i found decreased in freon r22 and the suctione line was freezed, i charged the ac with froen gas r 22 then i found that the suctione line changed and begin...


You are still low on freon. Charging AC by superheat and subcool
First charging a unit by superheat, this is only for Acs with an orifice or capillary tube.
Optimum superheat is 12° to 15° at the compressor or suction line outside the unit.
Hook up your gages and put a thermometer on suction line (large line), start the AC. Measure the temperature of the suction line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant, (you can also use a temperature pressure chart), now read the thermometer, let’s say the suction temperature( the thermometer) is 67° and the saturation temperature (the gages or temp. press. Chart), is 55°, subtract the saturation temperature from the suction temperature, 67°- 55° = 12° superheat.
Charging by Subcooling, this is for Acs with a thermostatic expansion valve, it’s common to see a sight glass on the liquid line (on these units with a sight glass just clear it, when, indoor room is at approximate set point of the thermostat). Optimum sub cooling is 12° to 15° at the outdoor unit.
Hook up your gages and put a thermometer on liquid line (small line), start the AC. Measure the temperature of the liquid line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant,(you can also use a temperature pressure chart), now read the thermometer, let’s say the liquid temperature( the thermometer) is 100° and the saturation temperature (the gages or temp. press. Chart), is 114°, subtract the liquid temperature from the saturation temperature, 114°- 100° = 14° subcool.

Oct 05, 2009 | Air Conditioners

1 Answer

Central A/C takes a long time to cool house


The system should be either R-22 or R-410A
You need to go outside and feel the suction line (the big line) with the unit running, after the house is cooled down, it should be cold and sweating,if the humidity is not to low, if it is your unit is probably ok. High Effeciency units
usually have a higher suction pressure and temperature and can run longer, if it's sized right. After the house is pulled down to temperature and starts cycling, it should come on and go off about 3 times per hour. The longer the unit runs the more dehumidification it should do.

Aug 22, 2009 | Air Conditioners

1 Answer

Improper Termperature Readings during AC run


personally i'd just replace the thermostat, but try pulling the front panel off and look on the circuit board and see if there is a jumper for F/C or any other settings. you may try changing its position. you can also remove the batteries for 15 minutes and see if it resets itself. the only other thing it could be is a wiring issue.

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2 Answers

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If you have a Gas furnace in the Attic then the answer is yes. The outside condenser will not run if in fact you have a gas furnace.

Feb 11, 2009 | Ruud Central System Air Conditioner

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