Original message
| Rocky112
 |  "Lennox 80UHG"
, posted Wed 31 Jan 12:06:  
I have a Lennox 80UHG2 the problem is It will work fine for 25-30 minutes after a cold start in the mornings. Then it will show code LED#2 ON LED#1 SLOW FLASH meaning that limit switch is open. I already run a check on the three limit switches and all are fine they will work fine for the period stated but after about 25-30 mins the limit switch will close but the system still show that the switch is in the open position then nothing happens till the blower timeout. If I move the thermostat to the off position the blower instantly kick in then I put it to heat and it will work fine for another period the problem is that this will happen before the desired temperature is reached. Seems if I do a reboot at the power switch it kicks in and work again or if I turn the thermostat off and immediately back on that also work. It does not have a problem if I try to go up 2 0r 3 degrees at a time. It will eventually get to the desired temperature at sometime in the day and it will maintain temperature perfectly once it get's there and if I set it to hold that temperature it will hold it perfectly forever. I already check all vents and put in the least restrictive filter and the same thing happens. I think the after a while the board does not read that the limit switch has closed back. During the normal opperation the switch will open for about 45 seconds when it does then it closes again. I changed the Thermostat and the same thing happens. Please help me. This might be useful info this is my first winter at the house bought it late spring the previous owner had a central air installed about 1 1/2 yrs before cannot say if he had these problems before or after it was installed.
Larry
[this message was edited by Rocky112 on Wed 31 Jan 12:46] |
| Replies:
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| yuri
| "Re(1):Lennox 80UHG" , posted Wed 31 Jan 17:15
I would suggest that you check the temp. rise through the unit. There should be a sticker inside it with the model # etc. and a rating for allowable temp. rise. Usually around 35-65 def.F. Get a thin cooking type thermometer and make a small hole in the supply duct about a foot downstream from the furnace and check the temp after it has run for 5 min. subtract the return air temp from it. You said the limit switch opens and closes with 45 secs. It sounds to me like it is getting weak from having been cycled too many times. Eventually they fail open. You may have a dirty A/C coil if the previous owner did not maintain the filters. This can restrict air flow. Need to check the temp rise to see if it is within limits.
Good Luck
Yuri
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| yuri
| "Re(1):Lennox 80UHG" , posted Wed 31 Jan 17:15
I would suggest that you check the temp. rise through the unit. There should be a sticker inside it with the model # etc. and a rating for allowable temp. rise. Usually around 35-65 def.F. Get a thin cooking type thermometer and make a small hole in the supply duct about a foot downstream from the furnace and check the temp after it has run for 5 min. subtract the return air temp from it. You said the limit switch opens and closes with 45 secs. It sounds to me like it is getting weak from having been cycled too many times. Eventually they fail open. You may have a dirty A/C coil if the previous owner did not maintain the filters. This can restrict air flow. Need to check the temp rise to see if it is within limits.
Good Luck
Yuri
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| | Rocky112
| "Re(2):Lennox 80UHG" , posted Thu 1 Feb 10:51:
I think I have a circulation problem I checked with the previous owner and he had the evaparator unit put in abaout 2 years before I bought the house. I switch the fan over to high speed and that does help a bit I can get it to do a 6 degree rise in temperature now instead of just three. I also located the damper vent last night and close it the motor was sticking. I did however open the cabinet and put a filter over it and it ran perfectly until it reached the desired temperature so I think I am having a problem with not enough air coming into the system. Hopefully I can find a solution quickly. But at least this morning I had twice the amount of heat I would have. I did not leave the cabinet door open last night but if I do then the system runs perfect. By the way the evaparator coil is clean and the filter is new. Thanks
Larry
[this message was edited by Rocky112 on Thu 1 Feb 10:53] |
| | yuri
| "Re(3):Lennox 80UHG" , posted Thu 1 Feb 11:04
Be careful if you leave the cabinet/bottom door open as you could suck fumes into your house. There should be a door switch which prevents you from running it without a door. Not recommended to run it w/o a door. Especially if you have a water heater nearby. Sounds to me like you have a lack of return air and may have to get some more ducts installed by a pro. The temp. rise method is especially useful and once you have the ductwork fixed you should be within limits.
Good Luck
Yuri
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| | Rocky112
| "Re(4):Lennox 80UHG" , posted Thu 1 Feb 12:34
Do you think I need a stronger motor the one that is in it is a 1/4 HP it is the original that was installed when the furnace was put in the a/c evap unit was added about a year and a half ago but the folks that was there never adjusted the temp for more than 2 degrees in the winter cause I see the programme in the thermostat manual. I does not give any trouble when it is asked to change 2 degrees even when the fan is in low speed. I could only it to increase by 3 or 4 degrees before trouble starts now that I close the damper vent it warm up 6 degrees this morning before it start acting up. I turn the thermostat off and immediately on and it worked good again for anothe rfew degrees by then the desired temp was reached and then all is well. Thanks
Larry
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| | yuri
| "Re(5):Lennox 80UHG" , posted Thu 1 Feb 12:44
I would recommend you check the temp.rise if you can. More than likely the motor is a bit small but putting in a 1/3 hp may not solve the problem if it is due to a lack of return air or too small ducting. The reason it is overheating is because when you set it back 2 deg. it does not run long enough for it too progressively creep up in temp. 3 to 6 deg. setback causes it to run longer and EVENTUALLY rise up in temp. to cut out on limit if you have a airflow problem. You should correct the airflow problem first. It worked fine w/o an A/C coil but the added resistance may be the problem/tipping point.
Regards
Yuri
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| | yuri
| "Re(6):Lennox 80UHG" , posted Thu 1 Feb 13:14
Let me know how many speeds the motor has. You may be able to increase the heating speed. Red is low, Yellow med, Black hi. You might not be able to fit a 1/3 in this fan due to the motor size brackets etc. Never had to do this. Usually correcting the ducts solves the problem.
Yuri
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| | Rocky112
| "Re(7):Lennox 80UHG" , posted Thu 1 Feb 14:56
The fan is a 4 speed I am not sure how to adjust the speed to get maximum out of it I switched the red and black terminals arround on the control board and it seem to run a bit faster and that did lead to better service do you know how to set max speed on the fan?. Let me know cause that is what I think I should try first. Thanks
Larry
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| | yuri
| "Re(8):Lennox 80UHG" , posted Thu 1 Feb 15:09
Black is the highest speed / normally used for the A/C. You can use it for the heat. Use the next lowest speed (Blue ?) for the A/C. Be careful that the A/C does not freeze up in the summer as it may need the highest speed. You may have to change it to black in summer. If you are having heating airflow problems your A/C will also probably be poor. That is why you need proper airflow/ductwork sizing. Do the temp. rise test as overheating the unit may cause premature failure of the heat exchanger and extra cost $$ to you.
Good Luck
Yuri
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| | Rocky112
| "Re(9):Lennox 80UHG" , posted Thu 1 Feb 16:56
I have a digital thermometer for testing body temp, would that work? also I have the damper vent closed now when it is open the system runs longer but that vent is very close to the furnace and with that cold air from outside it seem to take a longer time to raise the temperature and the inside temp also falls quicker when the system shuts off. I am going to raise the fan speed first to see what happens then do the test, or do you recomend the test first?. Then if both fail could I open a small section of the return vent in the far side of the basement to see what will happen? Thanks
Larry
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| | yuri
| "Re(10):Lennox 80UHG" , posted Thu 1 Feb 17:13
I think the vent damper you are talking about is a fresh air intake from outside into your return air duct, correct?. Uusally people open it if they have excess humidity in the house or cooking smells etc. and want to bring in fresh dry air. I would open it a bit. Experiment with it. It does bring in cold cold air which has to be heated. I have a HRV heat recovery ventilator in my house (Lifebreath) for ventilation. Try closing it and do the test. You need an insertion/stick type thermometer to get in the air stream in the duct. A cooking thermometer or a digital multitester with thermocouple attachment is what I use. Try the blue wire for heat and black for A/C. If it still too high after the test then use the highest speed for heating and try add some return air ducting as it sounds like your fan is having a hard time getting return air.
Yuri
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| | Rocky112
| "Re(2):Re(10):Lennox 80UHG" , posted Fri 2 Feb 15:01:
I had a HVAC company come out and look at it and the guy said I need a higher RPM fan. He said the ductwork is adequet but the fan need to pull harder. He said when the system was installed it was installed as a heating system only and the motor that is in there would be adequet for that but with the evaparator added it cannot handle the restriction well. That is one reason he think that the upper floor is always at least 5 degrees lower than the main floor. The vents upstears always have very weak air coming out. He recommend the motor change. What do you think.
Larry
[this message was edited by Rocky112 on Fri 2 Feb 15:04] |
| | yuri
| "Re(3):Re(10):Lennox 80UHG" , posted Fri 2 Feb 17:18
I am not sure that will solve your problem. The rpm of your existing fan motor will be the same as the new motor as they are multispeed and you can choose the rpm. If the motor is too small 1/4 hp at the top speed (black) it will be overworked/overheat/burn out prematurely with restricted ductwork and this is where a 1/3 might help. But it probably won't turn faster. I have been in the biz for 28 yrs and have never upsized a direct drive motor. Belt drives, yes. The physical size of the 1/3 may not fit well in your fan as I suspect it may be a quite small one. Cannot see it from here. Airflow problems are mostly due to ductwork sizing and layout. Your furnace was DESIGNED FOR A/C by Lennox and the fan capacity should be adequate. You can special order new furnaces with high output fans but that is usually not necessary. If he is giving you are fair price you may want to try a larger motor. You may want to get another opinion from a second company as it sounds like you may need some ductwork improvements. Sorry to spend your money but it may be worth getting another opinion and paying for the service call.
Good Luck
Yuri
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| | Rocky112
| "Re(4):Re(10):Lennox 80UHG" , posted Sat 3 Feb 01:28:
The system was originally installed as a HEAT only system the a/c was added 6 years later. He said that the fan in there now is 825rpm. He pulled the fresh air vent off so it could suck the air from the basement and open a part of the basement duct to allow more air but the same thing happen. He said if I get a higher RPM motor that would push the air through the system because the original was installed for heat only and was not changed to a upgraded motor motor when the a/c evaparator was put in.HE also advise me not to run the system with the motor door open like you said. I will get another openion but Two other a/c guys that I call who I never remember about said the same thing they live in N.Y. where I use to live. Thanks again for your help I really appericate the advices. The motor is a 1/4 Hp and is set to the highest speed. One oher thing he brought to my attention that I never think of The upstairs rooms are always about 5 degrees colder than downstairs and the vents upstairs you can bearly feel air coming through even when the door on the unit is open and it work without any problem.
Larry
[this message was edited by Rocky112 on Sat 3 Feb 02:18] |
| | yuri
| "Re(5):Re(10):Lennox 80UHG" , posted Sat 3 Feb 12:15
Good Luck Larry. Let me know if the new motor solves the problem.
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| | Rocky112
| "Re(6):Re(10):Lennox 80UHG" , posted Sat 3 Feb 17:02
I ran into a friend on the way home he was with a guy that does HVAC he came over and run several tests then he opened the area where the evaporator is and he said that that is where the problem lies. The space is reduced to about half of what it was they have a small evaparator in there so they block about 3 inches on each side all the way arround plus the restriction of the evaparator. He think it is a very poor installation. Now he said there are options that he will get back to me on.
Larry
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| | Rocky112
| "Re(6):Re(10):Lennox 80UHG" , posted Sat 3 Feb 15:42
I had to work today so I couldnt do anything.I was thinking, would putting in a primary limit switch with a higher limit point hurt anything? the one that is in there is the original and is a 175 degree setpoint. If I put a higher setpoint would that hurt the system.
Larry
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| | yuri
| "Re(7):Re(10):Lennox 80UHG" , posted Sat 3 Feb 17:08
It is illegal to change the limit control setting as the furnace is UL AGA approved. The duct is reduced to force the air thru the coil in summer. The only way around this is to install a bypass damper which you would open in winter and close in summer by the coil. It is usually difficult to install and work properly but a good tinman may be able to fit it in. Definetely worth a try.
Yuri
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| | Rocky112
| "Re(8):Re(10):Lennox 80UHG" , posted Wed 7 Feb 09:47
I bought a 1/4 HP 1625 RPM motor and put it in fire up the system and went a full 12 degrees in one go with no limit switch problem it works just like it is supposed to. Now I am happy and the place is as warm as I want it whenever I want. THANKS
Larry
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| | yuri
| "Re(9):Re(10):Lennox 80UHG" , posted Wed 7 Feb 10:44
Thanks for the reply. Glad you got it fixed.
Yuri
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| Service Manager
| "Re(1):Lennox 80UHG" , posted Wed 31 Jan 14:40
Stupid question (hopefully) but did you check the filter and make sure there isnt another one you dont know about?
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| | Rocky112
| "Re(2):Lennox 80UHG" , posted Wed 31 Jan 15:01
I checked but I did not see where there is another filter. That is not a stupid question it's all in the process of trying to fix the problem.
Larry
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