My furnace will kick on and heat and when the t-stat tells it to shut off the heat element cools but the blower stays on. I replaced the fan relay with a new one and it fixed it for a while but it's doing it again, sometimes. Could something be taking out the fan relay or is it in the t-stat or t-stat wires?
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Re: 1970's Rheem electric furnace
No the older rheems had a sequencer for the heat that turned on the blower at the same time that the heat strios are energized. so the first thing that you need to do is figure out the sequencer that is keeping the fan running and get it replaced.
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Sounds like the heating element has broken in two and is shorted to ground. even with only 110 to one side of the element and if the element burns in two and fall against the side of the frame it will complete the circuit and begin to heat up. Make sure you shut the power off to the furnace and then pull the heating element assembly and examine the elements to see if any are broken and shorted to the frame.
I'm not sure whether this is a gas unit or not. With many gas heaters, the blower comes on when the heat exchanger gets hot enough and goes off once the heat exchanger cools. Other things are happening before the blower goes on. The blower is normally controlled by a "fan control thermostat". This stat actuates the blower when the furnace is hot enough so that cold air is not being blown around and allows the blower to run until the furnace cools enough to get out the remaining heat after the flame shuts off but not so long to again allow cool air to blow around. If this fan control is malfunctioning, you will get erratic runs from the blower or the blower may not run at all or run long or continuously. The fan control is the first thing to check.
Try this----turn furnace off at stat and unplug furnace for 10 minutes. Plug it back in, the combustion and blower motor may both kick on for 2 minutes or so or not. Turn t-stat to heat and turn up stat to highest setting. Hurry out to furnace and you should hear the combustion motor(little motor piped to flue) kick on, then wait for a "click" next you should see a glow from the igniton element, then another click, next will be the gas valve opening. If no ignition, it will try 3 times and then lock ur *** out, and just turn on the blower just as a precaution. If you dont see the glow plug glowing after the first click, replace the $20 glow plug and you should be good to go. The glow plugs crack, and this is what breaks the connection. If you gas valve has a knob, and says pilot----turn the valve to pilot, push down on the knob, light the pilot and hold down knob for 2 minutes to heat up flame sensor. Make sure the t-stat is all the way down or off. After 2 minutes of holding pilot knob down, let go and your pilot should be still lit, if it is, then turn gas valve to ON and then turn t-stat up to kick on furnace. If ur pilot doesn't stay lit, get a new thermal couple and replace it-$12 bucks. Good luck and let me know how it went. email@example.com
You will likely need to install an isolation relay in the W circuit from the thermostat. Some thermostats rob a small current through the W circuit to power the thermostat. This small current can be enough to start the fan circuit timer. You can test this by disconnecting W at the furnace and allowing the timer to shut down. If the fan shuts off with the W disconnected you can install a simple relay.
The relay coil will be connected to Common on one side and the W from the thermostat to the other. Then you will run a wire from R on the furnace to the relay and from the N.O. Contacts to the W terminal on the furnace. This will kill that signal that is starting the timer and the W can steal it's power through the coil back to common.
POssible feed back thru tstat. This sometimes happens. Take a look at tstat disconnect w or white wire that goes to heater. Turn from heat to cool and abck and see if it does it again if not change tstat. You can get a good one at Home depot or Lowes about 20.00 easy to install Keep in touch Rus
Is there a setting on the thermostat for Auto or Fan? If so, make sure it is in the Auto setting. You will have a contactor that turns on the elements and a relay for the fan. Follow the wiring diagram to see which relay energizes the fan then unplug it to see if the fan stops.
The furnace could be shutting off on High Limit ...means your furnace is running too hot...check your filter and make sure return air vents are clean and clear....also it can be the Heat anticipator in your thermostat...which controls how many times your furnace cycles...basically your furnace should come on and off 5-6 times/hr ....need more info on your type of furnace and type of thermostat
when the room thermostat is satisfied it stops the heat by stopping power to the sequencer or contactor which is in series with the heating element/s...the TEMPERATURE OPERATED FAN SWITCH then takes over the blower until the heaters cool
If back-up heat comes on when a/c is turned on and then the back up heat turns off shortly after the a/c turns off, then the low voltage wiring is NOT correct. Your "R" terminal is basically your "hot" and your "C" terminal is basically your "neutral" to simplify explanation. The Furnace supplies the "R" power to the thermostat and then depending on what wire the thermostat sends the power back on determines what the system does. The thermostat terminals are as follows "G" is fan, "W" or "aux" is elect heat, "Y" tells the outdoor unit to run, "O" or "B" tells the outdoor unit whether it is heating or cooling, and "E" is emergency heat. "G" should connect from the t-stat directly to the furnace and go no further. "W" or "aux" AND "E" should both connect to your "W" or "W1" terminal in the furnace, there should also be a "W" connection to the heat pump ( this allows the H/P to turn on the elect heat when the unit defrosts) "Y" and "O" or "B" may or may not connect to a terminal in the furnace, usually they just pass through the furnace from the t-stat to the H/P and get wire nutted in the furnace. Now, here is the key. As I mentioned previously "O" or "B", a system will only use one or the other. The entire industry (except for Rheem and Ruud) uses the "O" terminial which has 24v on it when you are cooling and no power when you are heating. Rheem and Ruud use the "B" terminal which is just backwards, 24v in heating and no power in cooling. this could also be your problem if the t-stat thinks it is telling the H/P to cool but the H/P is actuall interpreting the signal to heat. Check your amp draw on the furnace, if you have anything drawing 15 amps+ then it is most likely the actual elect heat running, if not then check the "B" terminal. Most universal t-stats come set from the factory to use the "O" terminal which is more common. Usually this can be changed in the installer setup menu on the stat or sometimes the stat will have separate "O" and "B" terminals