short cycling

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Old 10-21-08, 07:06 AM
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short cycling

recently furnace has begun to short cycle it will even short cycle before the blower has even kicked on and then do it 3-4 during the heating cycle repairman tried turning the blower speed up when that didnt work he said the furnace is to big for the house and recommended added 2-5 new furnace ducts to allow more hot air out of the furnace that they would be glad to do for between $2500-5000 someone mentioned could be bad high limit switch how do i know for sure any other suggestion would be helpfull
 
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Old 10-21-08, 08:06 AM
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Originally Posted by krystalbay2005 View Post
added 2-5 new furnace ducts to allow more hot air out of the furnace that they would be glad to do for between $2500-5000
For that price, you could get a new furnace...


someone mentioned could be bad high limit switch how do i know for sure any other suggestion would be helpfull
Do you have a probe type thermometer? Do a temp reading for us, Stick it in the return near the air filter, and take a reading, and then after the furnace (above the A/C Coil). Let the furnace run awhile and we can see what you got for temps.

I'd like to know what the make and model of your furnace, and how big your home is? Also, what size air filter do you have?
 
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Old 10-22-08, 06:22 AM
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manufacturer goodman make:janitrol model#GMP075-3 home apprx..800sqft...filter 14x20x1....7 vents....have a probe therm. will try to check temp tonight......thanks
 
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Old 10-22-08, 06:48 AM
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Originally Posted by krystalbay2005 View Post
janitrol model#GMP075-3 home apprx..800sqft...filter 14x20x1.
Wow, that's an awful large furnace for a small house. Where are you out of?

Also, the air filter, where is it? Is it on the side return, or bottom return?

7 vents.
Supply vents that is?

When you do a temp reading tonight,turn the temp up high, let the furnace run 5 to 10 min.before you take a temp reading. I know you may get baked out of the house...
 
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Old 10-22-08, 07:00 AM
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in des moines, ia..filter is on the side return....yes 7 supply vents...2 of those are off of the same duct...thanks
 
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Old 10-22-08, 07:18 AM
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Originally Posted by krystalbay2005 View Post
in des moines, ia..
A smaller furnace could of been used, but hard to say for sure since I don't know in detail of your home. (how's the windows are, age of the home, amount of insulation in the attic... ect)

filter is on the side return...
Looking at the install manual for your furnace, it says on all model side return should have minimum filter size 18 by 25. (Not a common size, so I would say 16x25, or 20x25)

The small return may be the issue, but we will see what your temp results are tonight. the 14x20 gives you 280 sq inches of space, where it should of been 450 sq inches.. The return is almost half the size now.. Not really enough.
 
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Old 10-22-08, 05:13 PM
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cranked the furnace up to 85 room temp and was able to get a reading after the furnace temp reached 120 then burners kicked off temp dropped to 80 then burners kicked on again but went right back off keeps trying but wont stay lit if i turn the furnace off then back on the same thing happens the burners stay on long enough to reach 120 then tries to come on again at 80 but just goes on and off wont stay lit....it finally stayed lit after coming on and off 4-5 x's in a row temp above furnace reaced 120 then kicked off temp at filter was 75 at this rate with the on and off its going to take all nite for room temp to go from 70-85....so in a nutshell ..temp after furnace reaches 120 burners kick off tries to come back on when drops to 80 but has a hard time staying on....temp at filter 75
 
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Old 10-22-08, 05:26 PM
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do you know what the return/ house temp is?
 
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Old 10-22-08, 05:33 PM
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return home temp on thermostat is 70 cold air return vent #1 is 75 cold air return vent #2 75-80 furnace on for about half hour now thermostat only gone up 3 degrees...thanks
 
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Old 10-22-08, 06:26 PM
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now its to the point burners kick off even before ignitor is all the way cooled down
 
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Old 10-22-08, 06:58 PM
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if you suspect undersized return ..try and run it with the blower door off and all the interior doors in the house open ..did not notice if you gave the return duct size and how many return grills you have ..same with the suply duct size??does it light or try and light during a cycle??electric or glow ignition?sounds like high limit is touchy
 
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Old 10-22-08, 08:11 PM
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2 return ducts not sure of size at the moment .....i believe it is a glow ignition i watch it and it does turn red hot the ignitor allways comes on and the burners always come ... the blower always comes on... sometimes the burners will light and stay light for quit awhile other times the burners will light and go out right away ....there is really no rhyme or reason to what it does ....the problem is what the burners decide to do after they ignite....can i check the limit switch myself what does it look like..where at ..thanks
 
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Old 10-22-08, 09:47 PM
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Heating Repair

The furnace may be too big for the house but that is not going to trip the limit that fas even with a plugged filter and wrong ductwork. The limit switch is mounted in the firewall right above the gas valve. Put a meter lead on either wire terminal and if you read 24 volts at any time then the switch is opening you probably need a new switch but I would look at the ducting/filter/evaporator coil to make sure you have no airflow issues. if it is not opening then you are having flame recognition problems (look for a loose connection, possibly a bad ground)
 
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Old 10-23-08, 05:58 AM
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going to have to call a repair man today the furnace spent most of the night burners on then a few seconds later burners off then burners on a few seconds later burners off again if it was an airflow issue wouldnt the burners stay on for a few minutes atleast not burners on burners off burners on burners off if it does it enough times the system will shut down when it restarts because the room isnt at temp the burners will stay on long enough to feel heat blowing out but the then the burners start the on off game again until the system shuts down when it restarts you feel the heat blow out again then the burners on off again
 

Last edited by krystalbay2005; 10-23-08 at 06:17 AM.
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Old 10-23-08, 07:45 AM
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Yeah something is wrong with the flame senesor, or the pressue switch..

Keep us up to date what they come back with.
 
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Old 10-23-08, 03:33 PM
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repairman came out did a clean and and check said that was all it needed about 5 minutes after he walked out the door started doing the same thing called them right back he turned around and is looking at it again
 
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Old 10-23-08, 04:31 PM
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repairman just got done tore the whole thing apart determined that there was debris in the blower and that the blower speed was turned down way to low and wasnt pushing the hot air out fast enough i notice a huge differerence seems to be working fine now he did say though that if it happened again it is time for a new furnace .hope it doesnt come to that ...thanks guys
 
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Old 10-26-08, 08:30 AM
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Good to see you got it going... been working so far for you?
 
 

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