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Basics 09-20-2010 10:36 PM

Bryant Furnace Troubles
I have a Bryant 90i model 355 mav condensing furnace/with AC and it has a problem with going to high heat when the furnace call for heat. The unit
is about 5 years old.
I did a component test= ok and a pressure switch test= ok. There are no codes flashing to point to any faults. The service manual mentions that the condensate trap could be plugged. How do you clean it out?
Could the gas valve be the problem?
Any suggestions??

hvaclover 09-21-2010 02:54 AM

The drain goes to a floor drain or a pump. Use a shop back to suck out the the mold plug out of the tubing.

This might not be the problem since a plugged drain would flash a code.

Describe exactly in detail what you did and how the furnace acts.

Basics 09-21-2010 09:26 AM

Thanks for reply:
Basically I did the following.
1.Clean out air filter(pre start up for winter).
2.Power up unit and notice that the fan does not go to high speed.
3.Take off door and look for codes- none observed.
4.Pull off motor control cover and start looking for any loose wires or
screws that may be loose and also check the conditions of the hoses.
5.Repower and call for heat. Still no high heat. Fan runs on low rpm.
6.Go thru manual and perform component test=ok. Starts up and fan
goes to high rpm etc.
7.Next go thru pressure switch test. I get the 42 code that the manual
says I should get.
8. Repower and still no high heat( rpm stays on low). No led codes.
9. Furnace keeps house warm at present but not so sure in winter when
it gets real cold.
Thats about it.

yuri 09-21-2010 10:18 AM

Do you have a 2 stage thermostat. Is there a wire connected to the W2 terminal on the circuit board. May have to manually hold the door switch in and check for voltage from W2 (2 nd stage high fire) to C. If no 24 v there then it is not getting a signal from the thermostat which may be faulty or a wire is broken between the stat and furnace. Temp needs to drop at least 2 deg F B4 it call fore high fire.

Basics 09-21-2010 11:21 AM

Bryant Furnace Troubles
Thanks for reply.
I have a single stage thermostat. There is no wire connected to W2.
I did set the thermostat to call and I was not able to get 24v from
W1 to C even though the furnace started up, it stayed on low heat.
I went thru the thermostat and wiring looks ok, cleaned contacts on
the pcb board.
Should I be getting 24v somewhere on the terminal strip in the
furnace compartment, ie. C,WW1,Y/Y2,G or R ?
I guess if I don't get 24v there I may have a bad wire or more likely
a bad thermostat.

kenmac 09-21-2010 01:01 PM

if you have no wire at w2. What sends signal to gv to go on high fire ?

yuri 09-21-2010 01:03 PM

You should get 24 v from R to C. The furnace SHOULD NOT ever run w/o 24 v from w1 to C. That is the signal to tell it to turn on. It is now running wild and DANGEROUS. Label and remove all the wires from the terminal strip and try restart it. If it runs then the board is shot.

yuri 09-21-2010 01:06 PM

Carrier/Bryant/Payne uses a timed on algorithm with a 2 stage furnace using a 1 stage stat. Averages out the length of the last 10 cycles and calculates the best time to switch stages. Unique to them. Pain in the arze if you shut off the power as it starts over at 16 mins by default.


used that system on their mids also

Gotta give Carrier credit for not being stingy with technical support info.:thumbsup::thumbsup:

Basics 09-21-2010 01:18 PM

bryant furnace troubles
Sorry about that last reply. I do get 24v on the terminal strip C-W.
My volt meter had a bad lead. The 24v comes on when the thermostat
calls for heat.
I was looking at the schematic and noticed HI which is gas valve high stage operator.I believe this is one of the solenoids that has to open up to go to high heat stage. If it is shot it would stay on low heat.

yuri 09-21-2010 01:20 PM

It will take 16 mins of continuos running to switch to high fire. Read up about the adaptive timing in the last link I posted.

All this may have started because of a power failure. Why are you worried about it and what got you concerned? If you have a concentric vent, pipe within a pipe for the venting check under the outside hood for spiders webs,debris. Keep snow out of it in the winter and snowdrifts away so the exhaust does not recirculate into the intake and freezeup.

Basics 09-21-2010 01:48 PM

bryant furnace troubles
I was just reading the last link pdf you sent, excellent info, thank you.
I see now what you mean by having to wait 16 minutes. My concern was that high speed was not coming on, maybe my impatience. By the way we did have a power failure not that long ago, thanks for mentioning it. I hate when we get the brown out failures, they seem to do the worst damage.
I'll keep an eye on the time, but it seems that the house heats up well before 16 minutes so maybe the furnace doesn't get a chance to go to high speed before it shuts down.
Thanks for your efforts.

yuri 09-21-2010 01:53 PM

Yep. Will burn a few cubes of gas and some dollaros $$ running it 16 mins to find out.:laughing:

yuri 09-21-2010 02:40 PM

Ken, lots of brands use a 7-10 minute timer on the board to switch stages. They don,t use an algorithm method. Better to use a 2 stage stat if possible.

kenmac 09-21-2010 03:22 PM


Originally Posted by yuri (Post 505039)
Ken, lots of brands use a 7-10 minute timer on the board to switch stages. They don,t use an algorithm method. Better to use a 2 stage stat if possible.

Yep, knew some did & some use the t.stat.. Didn't know which his was .

beenthere 09-21-2010 04:44 PM

I think currently, only Goodman has a model that can't use a 2 stage thermostat.

I think Carriers early 3 stage units did use an algorithm to determine when to go from med to high.

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