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01-12-2013, 07:56 PM #1
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 ??
01-12-2013, 08:06 PM #2
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.
01-12-2013, 08:10 PM #3
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.
01-12-2013, 08:18 PM #4
01-12-2013, 08:18 PM #5
01-12-2013, 08:24 PM #6
01-12-2013, 09:21 PM #7
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.
Last edited by Labrat0116; 01-12-2013 at 09:36 PM.
01-12-2013, 10:32 PM #8
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.
01-12-2013, 11:07 PM #9
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.
01-13-2013, 12:41 AM #10
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.
01-13-2013, 12:45 AM #11
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. ??
01-13-2013, 11:48 AM #12
01-13-2013, 04:57 PM #13