1987 duomatic olsen hi-efficiency ultramax furnace

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  #1  
Old 04-19-09, 12:27 PM
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1987 duomatic olsen hi-efficiency ultramax furnace

Hi

New member here so I am sorry if this has been asked before. Last November I was given a free bottom motor/blower assembly as a spare from a reputable furnace technician while he was here giving my furnace the once over before winter starts. He told me that I have a good furnace and to not rush into replacing it just because it is old unless absolutley necessary.

About 1 month ago the original motor/blower assembly was acting up. I thought the problem was the motor but I decided to have him back just to make sure and that there were no other problems. The spare assembly was almost an exact fit and replacement except for the motor pulley being larger and the rails being longer. We used the original rails but had to drill a couple holes to make a proper fit. We installed this spare assembly and everything worked fine. I noticed shortly after he left that once the furnace shut off after heating the house that 2 minutes after it would come back on for 15 seconds then shut off. This happens all the time now. Twice I let it run and once it shut off on its own after heating the house, I would shut it off at the thermostate, but it would still come on for 15 seconds.

I did not call the technician back yet as I would like to see if I can repair this on my own and now that the warmer weather is here it is not that critical just yet to rush into it. I asked some knowledgeable maintanence people whom I work with and was told that the new motor/blower assembly has nothing to do with this new problem, it was only coincidental that it has started happening after the installation of the moto/blower assembly. I was wondering if anybody as any suggestions of what the problem could be and if this is an easy fix. Thank you.
 
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Old 04-19-09, 01:40 PM
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No HVAC Pro...but I'd guess , that unless you changed the pully back to the original size, its spinning the blower faster, thus removing more heat and bringing the temp to the set temp of the thermostat slightly faster.

Then the heat shuts off since the thermostat is satisfied. Furnaces have fan control switches that will turn on the blower when the heat exchanger reaches a certain temp...and turn it off at a certain temp. Its not ALL about what the thermostat does, some of it is within the furnace assy itself.

EDIT Oops hit the send button too early.

Anyway, when the house is satisfied, the burners cut off and the blower continues to run until it is below the "OFF" setting. Since you are moving more air (maybe) it cools off the surface of the heat exchanger and the tube that detects temp, then the fan shuts off. But since you are only cooling the surface of the heat exchanger, the residual heat will warm up the heat exchanger area, and turn the fan back on.

It may or may not be an issue, like I said, no Pro. I had the problem with mine and after verifying all the filters were clean and nothing was blocked, correct fan speed, etc etc..I just adjusted my fan switch a few degrees and problem went away.
 
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Old 04-19-09, 04:30 PM
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olsen furnace

Thanks for the advice Gunguy. I changed the motor sheave back to the smaller original size as you suggested but the problem is still there; coming back on for 15 seconds. It was definatly worth a try. It may be something unrelated to this motor/blower assembly.Any more suggestions would be worth trying. Thanks.
 
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Old 04-19-09, 10:16 PM
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Is the fan that shuts off and then comes back on or is it the burners?
 
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Old 04-20-09, 04:25 PM
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A higher speed motor (or choosing higher speed wires) may replicate the same thing Gunguy mentioned, regarding the pulley size difference.

I agree that you are suddenly cooling down the air within the exchanger, but then residual heat in the exchanger triggers the fan switch to come back on again until it is finally cool in the exchanger, once and for all.

See if you have a more powerful motor. And see if rpm speeds are listed on a plate on the motor. And if you have say 6 or 7 wires that come out of the motor where you have say a red, black and yellow? color wire (rpm speed selection wires -you choose one to hook up), along with maybe a couple of browns(capacitor), and a white(neutral), and a green(ground).
 
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Old 04-20-09, 04:33 PM
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I assumed the Tech would match the speeds...but maybe not go to the trouble of changing pulleys. It may not be related at all, and possibly a simple adjustment of the fan control would fix it. I'm not familiar with this furnace and didn't want to advise beyond what I posted. If I was there looking at it..maybe...but not long distance.

deerhunter..I will say this..do you have a silver (normally) box about the size of a pack of cig's visible? Maybe with Honeywell marked on the front?
 
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Old 04-21-09, 04:49 PM
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deerhunter,

Anxiously waiting to see if you are getting anywhere with this, per suggestions made by everyone.
 
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Old 04-21-09, 04:56 PM
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olsen duomatic

First of all, yes it is the blower/motor assembly that comes on and not the flames igniting for the 15 seconds. I removed the panel and had my thumb pressed on the switch to simulate the panel and watched it go through the cycles.

I compared the information such as the RPMs from the old motor with the new one and they are identical in every way.

There is also that silver box inside that says "Honeywell" on it with a white or creamish colored plastic knob with a notch in it. The box says "push man." and "pull auto".

There is also a low speed switch box inside as well. I remember when the tech. was here helping me instal this spare, he shut it off and told me to turn it on in the summer. I haven't had a chance to experiment with that switch yet by turning it back on.
 
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Old 04-21-09, 05:06 PM
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Olsen duomatic

I haven't really had a chance to look at it today as I work long hrs. but tomorrow is my day off and will look at it a bit more.

There is also something here that I should add. Yesterday when I was pressing in the switch while simulating the panel and it went through its cycles for some reason it did not come on for 15 sec. I thought maybe I found the problem being the switch. The electrician at work today said it couldn't be and that it was a fluke. I only tried it once as it is time consuming holding the switch in and waiting for the furnace to go through its cycles when you are the only one home. I will try it again tomorrow to see if it does it again. I appreciate everyones help and I am confident that I can solve this. Beer 4U2
 
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Old 04-21-09, 07:28 PM
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Deerhunter

The silver Honeywell box your refer to is a fan/limit switch. This device operates the fan based on temperature as opposed to the newer devices which control the fan based solely on time. Personally, I much prefer them to the time based fan controls. When the fan comes back on for the few seconds, it is blowing usable heat into the house & that's a good thing. If it bothers you, please let us know & we can tell you how to adjust the control to minimize or prevent the fan's coming on.
 
  #11  
Old 04-22-09, 06:45 AM
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olsen duomatic

It sounds to me what you are saying Grady is that there really isn't a problem. My furnace runs like a clock and I am happy with it. The only other problem I ever had with it was the exhaust fan housing ( I beleive that is what it is called) had rotted away leaving only a paint shell. I couldn't buy another assembly for $149.00 so I fabricated my own out of stainless steel at work and installed it. That was back in Sept. of '05.

Anyways back to this problem of it coming on for 15 seconds. Honestly I don't find it a problem at all, it is just weird that this is something new that has started after replacing the motor/blower assembly. I pressed in that Honeywell switch this morning and it does come on. Also that low speed switch that the tech. switched off when he was here last time and it also came on and then put both back to where they were. As I am writting this I was also paying attention to listening to the furnace, and again it came on for 15 seconds. Like I said perhaps there isn't a problem and I know from living in this house for almost 22 years and having that furnace for so long that this is something new. Maybe like you suggested it is better. I may try later again pressing the bottom switch in with my thumb and watch it go through its cycles to see if it still comes on as I did a few nights ago. Thanks to all and if there still is any more ideas or suggestions on this, please feel free to comment as I would like to know more about my furnace.
 
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Old 04-22-09, 07:30 AM
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The others can explain it better..but I think you should try adjusting the fan limit switch a few degrees. My way of looking at it is, this will extract the maximum heat from the heat exchanger, since you are paying for it..why not use it? Mine was doing that when we moved to this house, and I found it very annoying, esp when it would happen right as I was falling asleep. Our vents are a little noisy.

Also, it just seems to me, that the less the heat exchanger cycles from cold to hot and back, and the less times the fan turns on and off, then the less stress there is on the already old componants.

I believe you should adjust the "off" setting down by a few degrees, but that could depend on what its set to now. As I said, I'll let one of the others that have seen a few hundred of these things tell you more.
 
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Old 04-22-09, 07:59 AM
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By all means, if you guys think there is something I can do to eliminate this 15 second run on; I am all ears. I am not ready to throw in the towel on this old furnace and have it replaced just because of this and that it is 22 years old. I was told that it is 93% efficient compared to the new ones that are 95% efficient. I would like this furnace to run the way it is designed to. It is not to critical now with the warmer weather coming our way, but I just feel that if there is something not right it may lead to further problems down the road and I hate to have that happen during a winter deep freeze.

Please give me some ideas what to adjust and how. I noticed that honeywell limit switch only pushes in and out, at first I thought it would turn.

If I can get this solved I may put the larger sheave back on the motor for more air flow later on.
 
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Old 04-22-09, 08:48 AM
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You will have to take the cover off the limit switch to see your current settings. Normally its just 1 or 2 screws, then the cover will come off. There should be a dial with 3 tabs on it pointing to different temps. IIRC the upper one will be the high limit(?), next one down will be the ON, then the lowest will be the OFF.

You have to hold the dial and move the tabs with a small screwdriver or similar. You don't want the dial to move, I think it can mess up the calibration or the bimetal coil.

As I said, wait for one of the others to advise before making any adjustments.

If you can give the model number on the outside of the box, it may help. Should be on a label somewhere.
 
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Old 04-22-09, 01:19 PM
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Ok I will wait for more advice. I did what you suggested I do. I carefully pried off that silver cover as there were no screws. I see the dial with the three tabs but I will not touch it just yet.

I found when I was doing this, I noticed a green wire unplugged from were it was supposed to be. I plugged it back in and waited for the furnace to run. I noticed afterwards that it was only the ground wire.

There is some #'s stamped on top of the box and if I need to I will print them down next time.
 
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Old 04-22-09, 01:30 PM
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Did you note what the current settings are? The model # prob isn't that important, unless you needed to replace it. Write them down, but no reason to post them really.

Let us(them) know what the settings are.
 
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Old 04-22-09, 03:14 PM
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Ok I have the present settings. The top which says off is at 230

The middle off/on is set at 120 and the bottom pointer is at 100.

You are correct, as it does say "Do not rotate; hold dial when setting pointers". Now I have the settings recorded here and on a piece of paper. Just wondering which one to adjust for this type of problem that I have.

If an adjustment is all that is needed, then how did it get out of wack the first time when only the motor/blower assembly was changed. Perhaps the technician that was here helping me adjusted something that I was unaware of. Maybe I am jumping the gun here as I haven't tried playing with the pointers to see if that is the problem at all. Just waiting for the go ahead to "adjust something".
 
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Old 04-22-09, 03:34 PM
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Ok, since I'm here..lol
I'd adjust the off down to about 95 or so....you could go a bit lower, but the air might feel cold blowing out.

There may have been accumulated junk on the old fan, and when the new one was installed, even at the correct speed , was moving more air.

Did your tech (who seems like a good egg) clean your heat exchanger?
 
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Old 04-22-09, 05:17 PM
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Fan setting

Personally I think 95 is way too low. I think you are trading the short fan restart period for "cold" air coming out of the registers. I'd increase the middle pointer to 130 but that's me.
 
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Old 04-22-09, 05:37 PM
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And I'd defer to Grady....except...lol

I think thats what I did on mine (adjust the off a bit lower) and it works fine for me...but I'm in AZ...sooo....

Either one would prob work....I just like the idea of cooling off the heat exchanger as much as possible all at once. And sucking all the heat I paid for out....

As I said in the beginning...no HVAC guy here...
 
  #21  
Old 04-23-09, 07:11 AM
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I did set it at 95 and didn't get anywhere. Then I went to 110 and again nothing.

I was getting a bit frustrated so I called up the technician. Yes he is a good egg. His family are good friends with my two sisters' family and that is how I got to know him. He told me the same thing about what you guys are saying. He said it is just a simple adjustment there. He said he'll let me know when he is in the area and he won't charge me. I may still give him something for his troubles as I don't like to be indebted to. I am probably still going to give it a shot and bring it up to 130.

The heat exchangers were looked at in November and they are fine.

I appreciate the help to all. I am glad that this is not a serious problem.
 
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Old 04-23-09, 07:23 AM
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Yeah, after thinking about it...raising ON to 125-130 (and maybe dropping the OFF to 95, is it doesn't blow air too cold for your taste) would be a good bet. That 20 degree differential that you had just seems way too small.
 
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Old 04-23-09, 05:52 PM
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20 Spread

I agree. I think by getting a 35-40 difference between on & off your fan recycling will go away.
 
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