ReplyI have had that happen from old stats a few times. Try turning it up all of the way and maybe it will act different.
Regular Guest
Brand New Rheem RGPS Gas Furnace Short Cycling........ WHY ??
Long story short.....
We just had a new Rheem Gas Furnace installed in our home the other day. The Contractor is NOT finished with the install. They still need to hook up the return pipes as well as reconnect and recharge the A/C coil.
In the meantime, they got enough of the furnace installed to operate and supposed to heat until the can return to finish the job.
Before they left the furnace when through a heating cycle successfully. After they left, it started short cycling. Coming On for about a minute and turning right back OFF. We called them back. He checked some things out and said our thermostat was old and a POS and it will need replaced as well. He said he would replace it when they come back next week.
We've been on electric space heaters since.
I have my doubts about the thermostat causing the short cycling as our old furnace did not do this. A bearing went out on the squirrel cage and well as a bad blower motor.
I do know incorrectly adjusted fan limit switches can cause short cycling, but I can not find and documentation on our RGPS that shows a fan limit switch and/or it's adjustments. I'm assuming is it's in the electronic controls.
So why is short cycling and how can it be fixed ??
Professional Member*
I have had that happen from old stats a few times. Try turning it up all of the way and maybe it will act different.
Global Moderator
A possibility is the heat anticipater on thermostat has not been set to match the new furnace. That's something the contractor should take care of. Or he could replace the thermostat.
It is not likely to be a fan/limit switch as new furnaces us a PCB for fan timing. The limit will cause short cycling only if air flow is restricted.
Regular Guest
Thanks for the quick replies.
This the type/style thermostat that is currently hooked up.
Regular Guest
Thanks for the quick replies.
This the type/style thermostat that is currently hooked up.
Professional Member*
That's probably the problem, the heat anticipator on that stat is not set properly. A new digital stat should fix it.Originally Posted by Labrat0116
Thanks for the quick replies.
This the type/style thermostat that is currently hooked up.
Regular Guest
The anticipator is set at .1 right now. I just turned it up to .4 and see how it responds.
Well, the furnace blower came on and blew cold air for about (5) minutes and then it turned OFF. NO HEAT though. ??? It came back ON about a minutes later and ran until it came up to the thermostat setting and finally went OFF again.
The air coming out to vents is Warm....NOT Hot like it should be.
Suggestions ?
Last edited by Labrat0116; 01-12-2013 at 09:36 PM.
AOP Committee/Professional Member*
Depends on how things are situated, but with less negative Return static the blower could be delivering more airflow than it should. However, these newer furnaces operate at a lower temp-rise therefore the supply air may not be as warm as the old furnace's airflow.
Is the furnace the same Btuh Output?
The Tech should have checked on what the heat anticipator setting needed to be, & then set it properly for you.
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udarrell
Professional Member*
Somewhere on a data tag on the furnace there's a temp rise range listed. It would look something like
Temp Rise --- 35 - 65° F
The actual temp rise should fall somewhere near the middle of that range, or about 50° in my example. If the return air is 65° and the temp rise is 50°, then the supply air temp would be about 115°. If the ducts run through an unconditioned space such as a crawlspace or attic, then you can easily lose a few more degrees before the air makes it to the supply grilles. So the air is probably WARM, just like it should be. As udarrell noted, older furnaces tended to run much higher temp rises, in part due to their design, and in part due to airflow issues such as dirty evaporator coils and undersized ductwork.
FYI, there is no adjustment of any of the limit switches. They're all fixed and are there to save your life. Don't mess with them.
The short-cycling could be due to any number of issues, but at .1 your anticipator was definitely set too low. That number is actually supposed to be the measure of amperage flowing through the t-stat. On some newer furnaces that current can be as high as 1 amp. I had to set an anticipator the other day to 1 to accommodate the new furnace we installed. It was short-cycling, running about 1 minute max at a time before I made that adjustment. The installer had set it to .1 thinking that he had it on 1. Those numbers are pretty hard to read sometimes and the decimal points can be invisible in low light.
Regular Guest
Close I believe. The old one was 80,000 btu.......the new one is 75,000 btu 80%. The Tech said the old one was about 35 years old and was about 50% efficient.
I know he "should have" set the anticipator correctly before he left. Oh well...... They'll be back Mon AM to finish the job and install a new thermostat.
Regular Guest
Very good info!
The return air ducts are not yet connected to the "inside - 1st floor" return vent work. BTW, they are a pair of (12") ducts that run up there. The furnace is in a crawl space under the house. The return air is being drawn from that area. Not ideal by any means.
Anyways, the ambient temperature under the house now is probably in the 40s F. So that is probably why the supply air right now is luke warm. ??
Professional Member*
That would do it.
Regular Guest
I found a document On-line that shows the Temp Rise --- 40 - 70° F for this unit.
Going down to 23 degrees (where is the degree sign on the keyboard ??) by tomorrow AM so the Contractor best be here at 0830 like he said he would be!
God Speed, Jim. We'll miss you - 2-26-23
That will do it. That furnace is probably limited to a min return temp of 50. So leaving it to pull that air wasn't a good thing.
Professional Member*
LOL make sure your number lock is *on* ------> alt + 0176 -----> like this 23°
or go to your character map, it will be in there ---> start button---> all programs----> accessories------> system tools----> Character map
if this furnace is in a crawl space that is always cold, I would also have the contractor install a couple heat runs down there to keep the crawl space a little warmer. and insulate the crawl space
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Professional Member*
You said the contractor didn't install the combustion air inlet pipe. How long of a temporary pipe did he leave installed? Usually you need to have a minimum of 12" plus 1 elbow. Could be that the furance blew cold air because on the first attempt to light, it faulted out. The lockout sometimes requires the blower to run for 5 minutes before it will retry up to 3 times total.
50% might be a stretch. Maybe a 1920's gravity furnace... but a late 1970's unit, Probably more like 70%. The standing pilots hurt AFUE a lot. Heat output won't be a lot different, but it does sound like the airflow could be set fairly high.
Member
Sounds like we will be hearing more about this instal.
Professional Member*
Pulling return from the crawlspace? I'm assuming they'll correct that pronto as that's a big no-no.
Professional Member*
pictures would be nice.......of the furnace install......
Why am I the only naked person at this gender reveal party
Professional Member*
First-off, let the installers finish their job!
Nobody here has a clue as to your current situation being that the install is incomplete! If problems persist after installation is complete, then pictures may/can be helpful!
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