Author Topic: 1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!  (Read 7055 times)

Offline HVACR777

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1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!
« on: December 29, 2008, 06:11:27 PM »
I went on a service call and found this furnace with a bad surface ign. I replaced it and watched it's operation. on every other cycle the inducer motor would come on then the surface ign. the gas valve opened lit the gas and the heat exchanger would heat up and right before the blower kicked on the gas valve would shut off then the blower came on and ran for 90 sec. then the inducer then the surface ign.then the gas valve then lit the gas then it seemed to operate normally. I thought that this was odd so I checked all the safeties and the all checked out. This was also odd to me because this happened on every other cycle. I don't know if this is the normal operating sequence of a 1987 Carrier 80 plus furnace this is the first furnace I ran into that did this. Any input is much appreciated, thanks.

You can email me at tessiemichael777@yahoo.com it will go straight to my cell thanks

Offline Admin

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Re: 1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!
« Reply #1 on: December 29, 2008, 09:15:03 PM »
I assume the main blower is controlled by a control board and not heat activated.  I would verify I had a constant 24V at the W terminal during the cycling, to rule out any thermostat or low voltage wiring issues.  You mentioned after the first time it cycles off, the main fan will run for 90 sec.  This is consistent with the pre purge timing of that furnace, and would mean the 24V is being interrupted or the board is bad.

That's an old furnace, you might have a weak primary limit.  I would bypass it during testing and let the furnace run.  See if the cycling stops with the limit bypassed.  Test the limit for continuity using the audible ohm setting on your meter.  It might be opening and closing fast enough to interrupt the 24V and cause the furnace to cycle. 

But the fact that this cycling is consistent, to every other cycle, would suggest a faulty control board.  Tell the client the furnace has served them well and sell them a new one.  That kind of problem is ruining the efficiency of the furnace and will lead to other problems for sure.  The HSI is the first thing to go as a result of the cycling.

Offline ssmrjm

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Re: 1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!
« Reply #2 on: December 30, 2008, 10:54:51 PM »
i have seen this happen before if there is a humidifier connected to the hum. connectios on the board

Offline Zzz

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Re: 1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!
« Reply #3 on: January 15, 2009, 09:29:03 PM »
It appears to me that the fan is not coming on soon enoough. I bielive that furnace has an adjustment on the board for 30 or 60 second delay for the fan set it to 30 instead of 60.
Might be wrong but it's a guess.

Offline Zzz

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Re: 1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!
« Reply #4 on: January 22, 2009, 09:43:55 PM »
After reading this for the second time I reolized the problem.
Your IDF is not drawing quite enough you have to put a vacuum tee in line with the IDF and pressure switch (cold) and watch the vacuum go down after the flame starts ( as it always does) you will notice for a very short time it will drop below the pressure switch setting and flame will stop. Now on the second try the venting has started to work (with the draw fromm the heat) and is drawing better all is good.
It takes a lot of idf fan to get the venting to start working, you will see this a lot on the older 80mgf's and g24's (Lennox) furnaces.
Lennox is my game, I just fix the rest cuz I have to.

Offline acefurnacefixer

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Re: 1987 CARRIER FURNACE OPERATION SEQUENCE!!!!!!!!!!!!!!!!!!
« Reply #5 on: February 05, 2010, 06:27:12 AM »
I went on a service call and found this furnace with a bad surface ign. I replaced it and watched it's operation. on every other cycle the inducer motor would come on then the surface ign. the gas valve opened lit the gas and the heat exchanger would heat up and right before the blower kicked on the gas valve would shut off then the blower came on and ran for 90 sec. then the inducer then the surface ign.then the gas valve then lit the gas then it seemed to operate normally. I thought that this was odd so I checked all the safeties and the all checked out. This was also odd to me because this happened on every other cycle. I don't know if this is the normal operating sequence of a 1987 Carrier 80 plus furnace this is the first furnace I ran into that did this. Any input is much appreciated, thanks.

You can email me at tessiemichael777@yahoo.com it will go straight to my cell thanks
The board is bad...........the blower is comming on from the high limit tripping...........replace the board