Goodman Gas Furnace?

eddie grierson_3

Have a gas furnace that has been through two limits, Model# GMP100-5 80% using propane. Has 5 ton A/C coil on top. Gas pressures are good. Heat exchanger has been visually inspected from top and bottom / OK Indoor coil is clean, has .25" W.C. static. Did CFM check 1992 / OK Have ran blower on all speeds, only difference on low speed it will run 3 times longer before going out on limit.(removing more heat) Unit has 40 degree rise. Checked temperature at limit 200+ degrees.(so it's doing it's job) Going back tomorrow to due flue eff. test (Digital Bacarach). To check for CO level and flame impenging. Any suggestions or ideas? Thanks for any help in advance.

Eddie G

Mark A. Custis

Eddie:

Need to know what the manifold and supply pressure are. Are you sure the MGV is set up for Propane? What about the orifaces?

Try turning the limit away from the blower. The limit in question has a bad rep with me. Don't like them in anything.
Try taping your didgital thermometer probe to the end of the limit right on top of the snap-disc, and see if the switch is really seeing trip temps.

Often thought the exhaust pipe heat Xs get bent out of possition in shipping. Did a bit of feild engineering with a pry bar when I found the limit was seeing trip temps and all else check AOK.

Run the M/# & S/# past your local house, I do remember changing a few behind the inducer restrictor plates.

If you need more call me or email.

Good Luck,

Mark

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Unknown

Those switches are made by

I believe Texas Instruments. Pat Flaherty is here on the Wall from time to time and he works for them. Let me see if I have his e-mail address I will get back to you.

kf_2

Goodman Tech Support Line

(713) 861-2509

Mark Stokes - Technical Trainer

Extension 630

Mark A. Custis

Timmie:

I got spanked for mentioning brand names, but you read my mind.

Thanks,

Mark

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hot_rod

Limit

Hi Eddie,

I do not have much experience with Goodman but I have run into this problem several times with Carrier 80+ furnaces. How many returns does the system have? Dual returns (or one side and the bottom) are usually necessary on four and five ton blowers to get even flow across the heat exchanger. Otherwise, only half of the squirrel cage is seeing return airflow. Call or e-mail to discuss in greater detail. Good Luck! -DF


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eddie grierson_3

Thanks Mark

Incoming gas is 13"WC, does not drop with all appliances running including burner. Manifold is 10"WC. I attached temp probe to limit it is seeing up to 250 degrees.

eddie grierson_3

Thanks Dan

We met at Siggy's and Dan's classes in VA. I'm down here in Southern MD. It does have dual return boxes. Duct work checks OK with duculator and CFM caculation.

Eddie G.

eddie grierson_3

Thanks Timmie

Timmie I don't think it is a limit problem, I think it is a problem with the air flow through the furnace. I have ran unit with blower door off and with coil cover off and it still cycles on limit. I also need to get with you on a Commercial propane job I am having problems with. I have enjoyed the books.

Eddie G.

Unknown

Have you checked

static pressure on inlet and outlet side to see what possible restrictions there may be?

High static pressure results in low airflow. Measuring will typically reveal any condition which affects airflow.

Wethead7

Furnance

We found operating the fan on high speed heat or cool helps.
Also cut the manifold pressure back. You can go down to about 9.5 inches before cross lighting become diffacult. We have had this problem before the gas has to mant btu's.

Mike

Bill Barrett

Air flow through furnace

I’m leaning towards Marks idea, I think I remember some Goodmans needed a baffle or reposition of the limit.

Pat_4

Hi Eddie,
Sorry I didn't see this sooner. Mark Stokes at Goodman is a good place to start. Or try www.hvac-talk.com and post your question. If I remember correctly you may need some type of baffle plate. Another tech services rep for Goodman monitors this site, ask for Robin. Texas Instruments and TOD both manufacture the limits for Goodman, however it sounds like the limits are working.
Pat