Furnace fan cycles on and off every 2 minutes while burners are still on

this repeats until the house reaches temperature set on thermostat.

I believe it is some control on the fan that is faulty and tells the fan to shot off for cooling. But I do not know how to check it. any help and direction is greatly appreciated.

 

As a guess.....since we don't have a make or model of your system.....it sounds like the blower motor may be faulty and going out on thermal overload.

 

The syptom you describe is usually produced by the furnace overheating, then shutting off on the limit switch. The fan continues to run until the furnace cools off enough for the limit switch to again turn on the burners, which allows the furnace to overheat again.

Check to see if the limit switch is shutting off the furnace.

The most common reason for that happening is that something is impairing the air flow through the heating system, such as return air ducts covered over, too many warm air ducts closed, plugged furnace filter or air conditioning coil plugged up.

 

thank you PJmax. the make is RHEEM, model number RGDD-08NE-GR GN3D202 SERIAL 6841 F0989, but it is electronic ignition, possible original to the house, so 20 years old.

today when I got home the same problem was going on, the burners going but the fan had stopped, it switched the fan from auto to On as somebody suggested at work to see what happens, and that was the end of the furnace. it doesn't even light up anymore.

when i opened it up, the transformer inside the furnace enclosure was extremely hot to the touch, waaaaaaaaaaaay more than the burners that were only warm.

so I figured this much out. the power plug once it enters the furnace goes
to a box RHEEM NO. 47-19807-01 to that box (1) the transformer is attached, and also a honeywell box that has 1 wire to the transformer and one to the thermostat connections. there is also a relay attached to box (1)

also, the three wires -red, black, white come out of box (1) to the fan.

the transformer has wires to the thermostat connections and to the ignition control box ( robershaw MOD. SP 715A)

since the burners used to work, i am guessing the problem is now on box (1) and the relay? relay is essex 8903.

what and how do I check these?

thank you much.

 

Box (1) is just a junction box where the 110 gets split to different components, box RHEEM NO. 47-19807-01 is the fan control center that houses the transformer and the relay. there is no voltage out of the secondary on the transformer. i'll start there.

 

Well, you HAD one problem, quite possibly a limit switch that was opening as described earlier.

But rather than checking to see if that was the problem, you chose to continue with your own experiments, adding additional complexity and problems.

It's always a mystery to me why people ask for help and then ignore it in favor of their own inspirations.

 

thank you Seattlepioneer for you comments, i should have replied to your comment, sorry. the problem you describe is not what i have. in my case the burners do not stop, is only the fan that stops for awhile while something cools off enough that starts the fan again. I had already replaced the filters and the ducts are not covered.


the only experiments I have performed were some voltage checks. I replaced the fan control center (transformer and all) which burned up yesterday. the system works now as before, where the furnace works, fan and all, then the fan shuts off and cycles on again after it cools off for a minute or so while the burners are still on because the thermostat has not reached the set temperature .

The limit switch you refer to is the honeywell box that has a dial in it with the threshold temperatures? it still is at the settings that had when the system was working fine. however, from there i see that there are 2 sensor that i do not know what they measure. is it possible that they went bad? the next experiment is to maybe replace the sensors ( i do not know what they are called or what they do at this time.

thank you seattlepioneer. Please still help. thanks again.

 

I forgot to ask, how do I check the limit switch?

 

This Honeywell limit, with the dial in it, how many wires are connected & to which terminals? Is there a number on the inside of the Honeywell cover? Does it look like the pictures in Figures 5,6,& 7 here? https://customer.honeywell.com/resou...0s/69-0117.pdf