DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > System running Hot while set to "Cool" & "Off"




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Old 03-04-2011, 01:35 AM  
halogen49
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Default System running Hot while set to "Cool" & "Off"

Within the past week, the weather has been radical, ranging from cold nights to warm days. I had this problem during the winter as well, and I just used a portable ceramic heater to heat my room when I slept. I was afraid of letting it run while I was away, weary of it overheating the home and causing a meltdown.

The unit had cycled "on/off" in both modes (cold and hot) before as usual, but just recently, it would not cycle "Off" when it reached it's specific temperature. This occurred more during the "Heat" cycle. That would be the reason I left the power at the breakers set to "Off" while I was away.

I tried to run the A/C yesterday, and it would blow warm air. The outside unit is running, and it would cycle "on/off" when I moved the stat. Even after flicking the switch from "Heat/Off/Cold" quickly to try to unstick what might seem to be stuck did not work this time. While the switch is set to "Off" and the fan set to "Auto", the unit will blow and blow hot air at that. When I do set it to "Cool", the outside unit runs, but you can hear the inside unit cycling the furnace. Therfore, heat overpowers cold.

During the winter, the heater would not even heat, but would blow. After I gave up on it and left it off (I left the breakers off as well), I tried to run it again a week later. It started blowing hot again, but it would not stop when it reached it's set temp. Sometimes, I wouldn't even know if it was running right, because I would have it set on 72 degrees, and the digital gauge I have on the wall would show at least 77-78 degrees before it finally shut off. Other times, it would shut off at around 74 degrees (3-4 degrees makes a big difference when it feels like you're in a sauna). Sometimes, I would try to just turn it off, but it wouldn't. Even after a few minutes of it being set to "Off", it would just keep blowing. I would have to shut it down at the breakers.

This is a very frustrating problem, and I would like to know what the problem could be without calling for a repair.
Could this be caused by a simple fix? I did some searching, and looks like I might have a defective thermostat. Is this the root of this heating problem?

Any ideas are welcomed, thanks.



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Old 03-04-2011, 05:01 AM  
kok328
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Well, the first problem is that this condition is unusual and not easily remedied by prior known causes. In other words, what is going on here could be caused by many different problems that will require testing, inspection and process of elimination.
First you will need to know how to access the components of the system and have a voltmeter to test the various components.
However, on the surface, it sounds like it could be a bad thermostat, a bad/stuck contactor or a shorted control wire.
Do you have a volt/ohm meter to where you could perform some tests?



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Old 03-04-2011, 07:08 AM  
halogen49
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Yes, I have a multi-tester. I've pulled the thermostat off the wall and took it apart to see if there were any bare wires touching any of the contacts on the back of the board. I found no problem there, but the wiring inside the unit close by the fan shroud and the capacitor looks old. Like I said, the outside will cycle on/off when I move the temp switch, so at least I know it's cooling. I've also tested the copper lines and to the touch, the small line is hot and the large wrapped line is cold and getting wet.

It does sound like something is stuck like a contact. While I had that problem during the winter and leaving the power off for a long period of time, it seems as if it just unstuck on its own.

I forgot to mention also that earlier during the winter when the unit would not come on, I had tapped the thermostat a little and it finally came on. That's why I was thinking that it could be just a bad stat.

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Old 03-04-2011, 11:14 AM  
kok328
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I imagine that your system is a heat pump system of which I have very little experience. Here in Michigan a heat pump won't keep you warm.
Some heat pump systems have a heating coil backup for when it gets really cold, I suspect this is what you have. There would be a reversing valve on the condensor unit outside that reverses from cooling to heating. If this is not sufficient then the heat coils would come on to supplement and satisfy the call for heat. It sounds like whatever controls the call for coil heat is coming on regardless of mode (cool vs. heat) so yes, it sound like a bad thermostat. You can verify this by checking the voltage on the wires at the back of the thermostat and see which wires are energized during the call for cool. As far as the fan continuing to blow, this could be a stuck relay or a bad limit switch that opens the circuit after the unit cools down to X degrees. So there are a few items for you to check out and let us know what you find.

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Old 03-05-2011, 06:37 AM  
halogen49
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I'm really not sure what I have, but I do know it is an electric heater and not a furnace type. I bought a new Honeywell thermostat from The Home Depot, and it would seem that after opening it, I can not use it. The back of the old stat as O & B with no wires connected to it. It has W, Y, G, RH & RC. I guess that the RH would stand for "heat" as the RC would stand for "cool". The new stat has no RH or RC, only R and have jumpers for the O & B. It said that if I have any "2" of the following (R, RC, RH, 4 and V) then this thermostat can not be used. It would have been nice to display that on the back of the package.

Anyway, with no thermostat connected, I decided to turn on the breaker for a brief moment to just see if it was the thermostat causing this. The blower started blowing as soon as I flipped the switch, and there was warm air that quickly started feeling like it was getting warmer. Now that it would seem that the stat is not the problem, it could likely be that there is a stuck relay or something. I could not tell you about the voltage on the wires. When I found my multi-tester, the digital screen had a black blob on it. I pulled the batteries and the contacts are corroded. It's been awhile since I used the thing and now it's useless.

I will try to locate the contact itself and see if I can free it up later on today. It's raining right now, and I'll need to wait before I go rolling around on the ground.

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Old 03-05-2011, 06:50 AM  
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If heat and blower come on without any thermostat connnected to the system then you have reduced the problem down to shorted thermostat wires (the R wire is touching the W wire or the B wire depending on the system you have) and/or a relay is stuck in the closed position.

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Old 03-06-2011, 11:07 AM  
halogen49
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I traced the thermostat wire down and found that the white wire (W) was bare, then found that the red wire (R) was also starting to show copper. I suppose this was caused by the vibration, and they just rubbed together. After separating them, I turned the breaker back on and the blower motor came on instantly even with the thermostat set to the "off " position.

When that didn't fix the problem, I took off the cover to the relay switches, and tapped on each one of them. I heard no click sound of them being reset, so I pushed in on them and I heard a click on the bottom left switch. When I turned on the breaker, there was no blower motor. I flipped the switch to "cool" and the a/c started blowing cold air finally (even though it was cold in the house). I switched it to "heat" and it started heating the house, but when the temperature was reached, it did not turn off. I flipped the breaker back to off and checked the relay switch. It had become stuck again.

Could this now just be a weak relay switch?

http://i55.tinypic.com/16iaxk5.jpg
Bare wire


http://i53.tinypic.com/x3esxt.jpg
Stuck relay

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Old 03-06-2011, 04:42 PM  
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Unless the white wire was shorted to the red wire or another power source, it should not have caused the problems your experiencing.
However, it now seems to be that the problem relates to this bad relay.
I suspect that the relay is also tied to the blower motor which would make sense so that the heating elements don't burn up by heating without having air flow to cool them down (dissapate (sp?) the heat).
What you need to do now is get the make/model &serial number of your unit, label the wires attached to the relay and take the relay to your local heating & cooling company and see if they will sell you a replacement. Heating & cooling companies typically will only sell to licensed/certified repair men. If you can identify the relay in terms of function and rating, you might be able to find one online at places like Graingers.com or Newark.com or any other electrical component supplier.
Nice work & Good Luck.



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