Rheem short-cycling


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Old 01-08-17, 06:34 PM
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Rheem short-cycling

Hi folks - thank you so much for reading my post.

I have a ~3 year old Rheem that is part of a house we just purchased this year. It short cycles. It is natural gas 60,000. I have taken the blower out and cleaned it and the heat exchange as well as taken the coolant coils out and cleaned them. We have replaced the filter numerous times. In fact, the less restrictive of the air filter, the longer it runs without short cycling. With no filter installed it will run about an hour before shutting off. With a pleated filter we'll get about 10 minutes of run time. Since it does a safety hour off after a few re-tries it is getting cold and annoying. Any help is appreciated. All of the supplies and all of the returns are open - none closed. A central house return 12 inch is pictured in the larger blue color in my diagram below. Almost all of the supply lines are 6 inch flex, there is one 8 inch flex that goes to the basement. Neither the 6 inch or 8 inch flex going to the basement have any returns coming back, but the basement door is louvered. The bathroom and kitchen/dining also don't have a return. I feel like it's been like this since it was installed by the previous owners, the installation does not look 100% pro. CSST was not bonded, furnace supported by some scrap wood of odd sizes, lot of trash from install left over in the attic, etc.

The LED blink code is 3 blinks - limit switch.

Model RGTC-06EMAES

Any help is appreciated, it seems like air flow? But not sure what the answer - more supplies? loop back into return? more returns? Maybe it's not air flow, you all hopefully know the best place to continue troubleshooting. I've figured out enough to clean it all, but now I'm out of ideas. Thanks.

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Old 01-08-17, 06:43 PM
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Any provision for changing the main blower speed?

Try running it with the blower compartment door removed and the safety switch taped down. If it doesn't overheat, that would suggest too little return air....
 
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Old 01-08-17, 06:46 PM
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Thanks for the quick response. I'll give that a try.

Regarding the blower speed, I saw some info on that in the manual - but it wasn't clear to me how to adjust that. Is that something that is adjustable on the unit itself or the thermostat or any ideas on that part.. thanks.

Rheem RGTC-06EMAES - Classic Series 95 AFUE Downflow/Horizontal 60K BTU Gas Furnace --- 1369225414910
 
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Old 01-08-17, 06:56 PM
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Gemaire/article_1369225414695_en_ii.pdf?fmt=pdf

On page 48 is the method for checking heat rate-of-rise.

The last page of the installation book is the schematic.

Remove the blower door. Tell us what color wire is on the.....
FAN terminal -
COOL terminal -
HEAT terminal -

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Old 01-08-17, 06:57 PM
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The installation manual linked to at the site you linked has the full procedure for measuring temperature rise and setting the blower speed in the "air flow" section of the install guide.

Essentially you measure the temperature rise across the furnace and adjust air flow so the rise is within the design range of the furnace. It should have been done during installation.
 
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Old 01-08-17, 08:28 PM
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I have a Rheem furnace that was short cycling for years and never knew why until recently, even with a few techs coming out to look over the years. Just something to look at.

A tech came out recently and said it is the diameter of the vent pipe, mine is only 3" and needs to be 4". This was overheating the furnace and high limit switch.
 
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Old 01-09-17, 07:16 AM
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Thank you for your patience. The heat has the yellow wire going to it shown in the photo.... do you think it should have blue wire instead?
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The exhaust pipe is 3 inch, maybe that is related. Shown below.
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Old 01-09-17, 08:45 AM
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Yes I would use the blue and see if that stops the limit from tripping.
 
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Old 01-09-17, 09:59 AM
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Thank you all for the responses. I put in the HIGH from the COOL just to give it "a whirl" and it ran non-stop for almost an hour and went from 69.5 to 73.5. I've now plugged the black into the COOL and plugged the blue in, and it is still running fine. I think this will help big time! I suspect the folks who installed it didn't test it, or maybe someone modified the system afterward. Probably was installed in summer when this issue wasn't noticeable. Thanks so much for all who responded. I'll post an update in the next few days if it's still working
 
 

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