Forced Air Natural gas Heater keeps cycling on and on

"extremely puzzled"'s Avatar (by Gravatar) by "extremely puzzled" in  Climate Control » Heating 

I seem to have a difficult to diagnose or explain problem with the Main House Heater Unit:

It is an Amana Air Command 80 (c 1986 mfg date).

This started sometime last winter heating season (2012-2013) but took so long to figure out that there was "something " going on that the season was over and we just figured it might be due to warmer than usual winter here.... or whatever...

But its been so long since I've seen a "normal" cycle of Heat from this Furnace that I can't for the life of me remember it properly.

I seem to recall that a Heater goes on with flame....heats up heat exchanger....then the fan comes on and blows it around the house.....flame goes off and fan runs until its too cool for use then it closes down

Then cycle begins again!

What happens last year and this heating season (did not occur with the Air conditioning cycle this summer) is that the thermostat says calls for Heat.

Then the flame goes on

then it heats up the heat exchanger tubes

the fan comes on and blows and flame goes off as its supposed to

but then the thermostat?? or maybe its the computer board onboard the Amana Furnance that is now calling for MORE heat while the fan is still running, blowing the old series of heat!!

And the crystal lights the flame----but suddenly the Thermostat or the Heater "wakes up" and says the fan has already done its job, so it turns off the fan while the new series of heat is working to heat the coils.

Then after the exchanger is hot again something tells it that well we'd better turn on the fan to move this new heat around the house

and on and on it goes.. re cycling the process "shorter" heat cycles and more and more fan on and off cycles

This can't be good for the crystal starter element--

or the FAN going multiples times on and off and on and off......

and its certainly hot enough as the thermostat does not turn off "early" its just running spending more gas money spent running the heater before the fan has completed its job!!!

So far I investigated a few things with some local help (who is puzzled and can't fix what is not "broke")

I found the "fan limit" switch cycles from 100 deg set point to its 200 deg upper limit within a few minutes of the gas jets turning on. Then as a safety feature (I just discovered) it turns off the flame and keeps the fan running. I watched while the fan limit (and it bi-metallic probe in the heat exchanger) rapidly cooled down and then once its below 150 degrees the thermostat which is not satisfied yet, calls for more heat and the cycle repeats over and over again. Thus the house heats up very very slowly doing this cycling method.

Again someone helping figured maybe there is a vent blocked in the registers or return ducts. I opened up a few ducts since then and found almost zero dust, just clinging to the sides of the duct leaving 99% open and free for air to move. Now I also have an Honeywell Electronic air cleaner mounted at the final section (largest) return ducts just before they enter the Amana Furnace. Its been there 30 years with one or two models before that! Everything worked fine.

But mysteriously when I had the "cover" off the Honeywell air cleaner, the system WORKED PERFECTLY!

Now before you say "dirty filters" as an answer, we just washed the entire unit (not that regularly but it was washed in dishwasher as required before the winter season started) and we got a brand new set of pre-filter screens too---I even switched back to the older screens for testing (both made of metal you wash them....but older one had more holes) which I got specifically to wash them more often (but this is before the unit came on again this winter heating season with the same mysterious defect.

One other thing (I could send some photos as I did to this site on a question last year, if you want to see it) the person who installed the Amana 30 years ago, with the existing Honeywell back then cut TWO additional vent holes and covered with decorative vent covers right on the final return before the Honeywell (so there has been always two huge gulping air vents taking the cooler air from the HVAC room back upstairs to recycle it a bit from the downstairs areas.

Just weird that only by opening the cover door to the Honeywell (don't have to remove the unit! but it helps to give it more return air) the Amana and Thermostat and everything and heat limit switch all works perfectly!

I make jokes...I said aha! Racoon in the vent! but its not able to do that and we've never had anything in the vent systems and all registers that I could remove with a screwdriver and vacuum (and got a long long dryer vent scrubber too) are cleaned now spotlessly....

Yet still frustrated by this condition. Before we call in others who will just sit there spending money investigating (as one person said scratching their head who came that they had no idea where to begin once I showed them the Honeywell door open and everything working!), has anyone out there heard of a problem like this? Googling the answer I can't get close to it as I'm certainly not a HVAC person and not using the right/correct terms to locate anything on the web.

Thanks for reading this very long explanation!

"extremely puzzled"

(sorry for the "" marks I can't edit them out they do not appear on the edit page!)

Know the answer or have a comment? Post it here!

Answer by stanhvac1

It sounds like you have a restriction in the ductwork ahead of the air cleaner. If the ducts are insulated on the inside it is likely that the insulation has come loose and is blocking the ducts. Remove the air cleaner and take a mirror and flashlight and look into the ductwork from the air cleaner back toward the return grills, and also check from the closest vent looking toward the airhandler. It is also possible that the heat exchanger is stopped up. How long has it been since the unit was thourghly cleaned?

Answer by

Thanks for your information! I suspected something I jokingly called it a "racoon in vent" but nothing even smaller animals ever manages to get in. Interesting that there is something like insulation in those big square vents which can actually dislodge and block the vents! The ones I can see running across the ceiling in the garage (rest of house is 100% finished so no views are available), but I did remove a number of registers and as far as my camera can see down the vent they look open, but that is only a foot or so before they take sharp turns and who knows what is down there! I took a long vacuum hose down a few (mostly clean as we have electronic air cleaners for over 40 years) and I have a dryer vent thing with big whisks on the end but it too is only 3 feet long and lots of the system is totally in the dark as to what could be blocking the return duct.

In the meantime, I had finally chosen to have a tech come over and check it out and they told me stuff which is in my other questions on this site See my question: " Dirty AC Evaporator coil blocking air flow to nat gas forced air Heater---can I clean it myself? "for more information maybes that would help you in this discussion thread...

To directly answer your question you asked me, no, none of our service people ever mentioned that either our vents were dirty enough to be cleaned out, or the evaporator coil was getting caked with dirt over the years as no one ever bothered to look inside I guess until someone cut a hole in the side of the unit and looked in with a camera!

Thanks for your reply again!

"extremely puzzled"

Answer by stanhvac1

A dirty evaporator coil will restrict air flow. A sign of that would be iceing in the cooling mode. A dirty blower wheel in the furnance will also restrict air flow. If I read the first part of your question correctly, you said the air conditioning worked properly which would indicate that not being the main reason for an air flow issue. 1. Where is the evaporator coil located in the system? I am assuming the air flow picks up when you remove the air cleaner since you said the heat works properly with it removed. If the eveporator is between the furnance and the air cleaner where it should be and was causing the problem, removing the air cleaner would not have any effect on the system. A good hvac technican should be able to isolate your problem in approx and hour or less by using checking the static pressures on the return and supply side of the system. Static pressures will show restrictions and air flow issues. I am still seeing indications of a restriction in the return duct or a possible colasped duct by your response.

Answer by

Thanks for your reply stanhvac1 !

I have something called photobucket which works at this site very well, used it last year for another situation. I'm trying to post, but have to remember how. Will show you the Amana Air Command 80 with the Honeywell air cleaner at the left and on top of the Amana unit above the heat exchanger is the A framed evaporator coil in a black box since 1960. Above that are the ducts for the outgoing heater (or air conditioned) air. At the left before the Honeywell, all the returns combine to a huge 40x20 return before it enters the bottom of the Amana unit where the fan unit you mentioned is housed.

When a tech opened up the unit, the floor of the returns is spotless, got not a smudge of dirt on his jacket as I can reach through and vacuum it at least twice a year. The fan unit I cant clean, but upon removing it there was a few dirt balls, which I got rid of by hand.

The main problem seems to be the evaporator coil, and a camera view (see my follow up question here at Homeowners hub titled: " Dirty AC Evaporator coil blocking air flow to nat gas forced air Heater---can I clean it myself? "for more information maybes that would help you in this discussion thread...

That showed up on a flexible tube camera to be almost totally blocked off with dirt.

I hoped I described my arrangement better to you now.

If you still would want to see the photos of the units ... I can post them, let me know I'm still trying to do it anyway if I can remember how I did it last year. The tech who came by with the tube camera....said he can't make a copy of the photos from the tube camera---I think he can but didn't want to give it to me)

Oh, to answer your first question which I missed, no icing during the summer on the Air conditioner pipes (large or small) and this summer fully charged up the Freon as had lost some over last year due to the problem in another earlier posting.

Thanks for your reply again!

"extremely puzzled"

Answer by stanhvac1

Thank you for bearing with me in trying to assist you. It is diffucult to isolate some issue's quickly without being able to see the system personally. I did read your other comment a few minutes ago on the dirty coil.
Back in the 60's we did some stupid installs due to less knowledge than we now have. To answer your question of cleaning the coil, the only way it can be properly cleaned is to remove it from the furnace and wash it with coil cleaner. Regardless of what you have been told it can be done. I do it all the time and granted most of the time it requires extra work cutting it out of the box and making a new cover when reinstalling it.
1. Stupid install: The evaporator coil should never be downstream, (after the heat exchanger). It should be on the return side of the unit.
2. I will need you to picture this in your mind as I explain it. Let's think air flow since that seems to be the issue here. Please bear with me here as I am trying to get a picture in my mind of your situitation. First: if I understand correctly, everything works properly with the blower compartment cover and (or) the air cleaner removed which both are on the return side of the system. So the flow of air is through the blower to the heat exchanger to the evaporator coil and into the supply ducts. I am going to use a water circuit to demostrate this, see pitcure below.
A. with valves 1,2and 4 open, valve 3 closed we will get 60 psi water (full air flow) through valve 4. If we close valve 4 (Totally blocked evaporator) no water comes out, (no air flow). Again, open valve 4 we get full flow.
B. If we close valve 1 half way we will get 30 psi through valve 2 and 4, (restricted return).
C. Leaving valve 1 half closed, valve 2 and 4 open (30 psi). Now we fully open valve 3, (remove the air cleaner or blower compartment door) we once again get 60 psi through valve 2 and 4.
I hope I am not losing you onthis but this is the reasons that it appears to be a return side restriction verses a supply side restriction unless I am not reading your comments properly.Also, I would like to know the size of your air conditioner as a 40x20 return is good for 7000 cfm which would be a 5 to 6 ton air conditioner.

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