Trane Roll Out Problem

[jim22]

I need a little help,I have a Trane YHC120A3RHAZKBCC. THe unit was installed a 2 years ago. This is the first time I have worked on it. I found 2 old roll out switchs laying in the bottom. The roll out switch was open on my arravial. Replaced with a resettable trane swicth. The unit sounds loud(Flame roaring ) I have 3.5 WC before and after the gas valve. I removed secound stage heat and it is still tripping (ros). It takes a day or so for it to trip. Induser is clear good volume. Indoor blower running correct direction and at speed.
I'm a Refrigeration guy that does some heat. I know I should leave it to the experts. Thanks a head time for the feed back.

[HVAC LLC]

With the 2 old roll-out switches left on the job, sounds like it could be a problem from day one. I would look at the combustion blower fan, maybe an obstruction in the small fan cage. Can you compare it with any other units on the roof? Could be a problem with the fan quitting when it gets hot, or runs for a while, amp it out and see if it is within specs.
Good luck.
HVAC LLC Jim

[jim22]

Check combustion blower it has good air volume screen is clear this the only trane on the roof the others our Lennox.

[HVAC LLC]

I would call Trane's tech line, I assume they have one, and give them the model, serial and type of problem, could have been a bulletin on that model.
Hang in there...

[HvAckid82]

HX might be cracked....is this a down flow unit or horizontal discharge?

[oldtimer2]

sounds like you have a bad HX. 2 years old, I would check air flow on ID fan. Check delta-t. It should not rust-out in 2 years, if you find cracks, I suspect overheating. Good luck!

[ldmth44]

Sounds like you need to inspect the HX. Cracks may be evident. I agree with others about checking delta-t and fan speed (if possible) or duct configuration. Could be overheating.

[maxpower]

I could be wrong but,isn't that a negative pressure unit?

[gwoner]

These units come with an extra roll out switch when shipped. Should have a manifold press. of 1.8 iwc for 1st stage heat or low fire and 3.5 iwc for high fire or 2nd stage. Your min supply pressure should be 4.5 iwc

[HvAckid82]

max,
When you say negative, you're talking about negative pressure in the HX? If so even with a negative pressure system a single crack in the HX (with the indoor blower on) can cause the flame to roll out. Check the flame when the system starts(before the indoor blower starts). As the HX heats up and expands the cracks get bigger and the blower starts and the flame will start dancing. It's amazing how many units are started up improperly. Air flow is the #1 thing with HVAC equip.

[ludicrousspeed]

Did it have a tamper proof cover on the gas valve? Could the flue exhaust being affected by wind? or a good old cracked heat exchanger.Negative gas pressure, sealed combustion,gas valve on the intake of the combustion inducer?

[ascj]

That is a Precedent series unit. It has a normal inducer with in shot burners. It's not a negative pressure burner.

That be said, if it's setup for down flow, it's very easy to inspect heat exchanger. Just remove the horizontal supply panel. On that unit if your getting flame rollout its normally a heat exchanger problem.

The rollout that is installed is for downflow config. They then wire tyed a secound rollout on the back of the inducer, for horizontal discharge.

[ascj]

bump

Why the bumps? Can someone take care of this person?