Lennox RTU, manifold pressure

[Slim_Miller]

Working on a GCS16-653-125-3J. Im not to familiar with these units. My issue is my manifold pressure jumps up and down. From a high of 2.8" to just below 1". I have a rock steady inlet pressure of 6.6"
Any help would be great.
Thanks

[b-roq]

Gas valve.... dont think those rtu's have slow opening gas valves but could have crap in the gas valve. I'd replace.

[Slim_Miller]

This is the 2nd valve, original valve did the same thing.

[2sac]

I believe 2.8" lowfire and 3.7" wc highfire is what you should have

[Liamd8]

Two stage valve?

[Slim_Miller]

Its single stage, Manufactures specs call for 2.7".

[hvacrmedic]

Sounds like you may have a manometer issue. Cracked hose?

[Liamd8]

Is that model one with the " gun type" burner, where the inducer mounts with the gas line and blows the flame into the heat exchanger?

[hvac wiz 79]

A little off topic but I hate gcs units.

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[Slim_Miller]

manometer is six months old and my hoses are fine. The same hose and meter was used to test all my other pressures at the same time.
The burner is kind like an in-shot, the heat exchanger is kind of diamond shape to tubular to combustion fan. If that makes sense?

[emtim]

what kind of issue you having with unit , I had one giving me problems it was heat exchanger ,new exchanger replaces the one inshot burner design.

[Slim_Miller]

I'm getting low temp rise, 15 - 20 deg F. Manufactures specs 40 - 70 deg F. Indoor fan speed is ok, im not getting any outside air in, and i tried to clock the meter, i couldn't tell the scale of the dail due to the age of the meter. My guess is that im only burning 61000 btuh. Units input is 125000.

[hvac wiz 79]

And the inlet stays at 6.6" the entire time?

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