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generalservices · Jan 22, 2009, 07:08 PM

I have a 8/9 yr old Nordyne gas furnace. I am remodeling this home and at night I shut the heat off to save energy. When start in the morn. I turn it on and set the theromstat at 65 deg. And it will start up and run but before it reaches what ever temperature I set it at, it will shut the burner off and cool down as if it has reached the required temp. With in a min. or less it will start all over again. Some times after it shuts down and as soon as the blower stops, it will start up again. If I jumper R & W it will keep on running and heat the house until I disconect the jumper. I have run new 14/3 wire from elect. Panel to the furnace and checked voltage, (123 v), polarity, grounded the furnace, run new 18ga. Thermostat wire, tried 3 different thermostats. Checked the ohms on the gas valve wire, (4.4ohms) and set the anticipator to 4.4. There is 24 v. going to the board. The condenstate line and inducer vent are clear. The thermostat is mounted on a inside wall. I even remounted it in the center of the room temporarily as not to pick up the cold from the plastered wall. How can I keep it running and get up to the desired temp?

generalservices · Jan 22, 2009, 07:15 PM

Added to generalservices question. I also put in a clean filter.

mygirlsdad77 · Jan 22, 2009, 07:38 PM

You say you jump r and w and furnace work fine? I would start by replacing thermostat. Can you tell me if your current thermostat is a has a mercury bulb?

Also, you say you are remodeling. Is the house stripped of insolation? What you are experiencing is called short cycling. In your case, it sounds like it is being cuased by thermostat(whether it be the thermostat itself, or thermostat being exposed to extreme temp changes in the house. I really need more info, but I would be willing to bet that you need a new thermostat. Please let me know what you find.

generalservices · Jan 22, 2009, 07:51 PM

Thanks for the reply. It does have a mercury bulb. The house is insulated with thermo windows, but it will be 35 to 40 degrees in the morn. When I start. One of the 3 thermostats I tried was a new one. All are Honeywell's. Thinking of trying a White Rogers or some other brand.

mygirlsdad77 · Jan 23, 2009, 04:30 PM

I would stick to honeywell. They are as good as it gets.

Just to make sure, jump r and w again and make sure furnace operates correctly. I know you have already done this, but I want to make sure that the thermostat is the problem. The problem may lie elsewere, just need to make sure what we are dealing with.

Have you cleaned the flame senser?

generalservices · Jan 23, 2009, 05:43 PM

The flame sensor has been cleaned. This AM it was 32o when I got tp the house. I jumped R & W and it ran for 2 1/2 hr steady. The temp got up to 60+ so I hooked up the thermostat and here we go again. Same thing. I set it to 70o and at 60o the burner shut off, the fan ran and cooled the plenum down and shut off. As soon as the fan stopped, the inducer started up and the process starts over. I was there till 5:00 so I just jumped it when it got cold. I checked with a hvac guy, and he said, (beats the hell out of me). This weekend I may try a different brand of thermostat.

I called the tec @ Nordyne and all he said was that if it starts up again after it shuts down, that means it's calling for more heat. What gets me is that you can stand there and watch the thermostat bulb go from left to right and then back again in a matter of seconds. At one time I was able to detect 5 volts between W and ground just before the inducer started up. Once it started the voltage went to 24 volts ( W to ground) It was as if there was voltage feeding from R back through the thermostat. Could this be screwing up the anticipator somehow?

What I need to do is get away from it for a while and then look at it from a different angle.

mygirlsdad77 · Jan 23, 2009, 06:13 PM

Originally Posted by generalservices

What gets me is that you can stand there and watch the thermostat bulb go from left to right and then back again in a matter of seconds.

This is definitely your problem. You may be able to set the heat anticipator(if you have a tester that shows what the setting should be). I would replace thermostat. Honeywell is still your best bet. No brand makes murcury thermostats anymore, they are outlawed(due to the murcury). Get a good honeywell(or whatever brand you choose) digital or electronic thermostat that is compatible with your system. It you have gas forced air, with or without ac, I would recommend the honeywell PRO 5000, Good, simple to operate thermostat that is very accurate in keeping temp constant in house. If you do get this thermostat, let me know exactly what style furnace you have, and I will walk you through setup of thermostat. Your problem will be cured, I almost guarantee. Let me know what you think.

wmproop · Jan 23, 2009, 06:32 PM

Another nickels worth of maybe not needed info,, if you have tstats with mercury bulbs in them they have to be level,, or they will be out of calabration sometimes pretty bad,, as to why its cutting off before the temp. point of the tstat

mygirlsdad77 · Jan 23, 2009, 06:45 PM

wmproop makes a good point. However I believe that an out of lever mercury thermostat will only affect accuracy of stat, but won't cause bulb to roll back and forth quikly the way you say it does. I think the coil spring in your thermostat is just plain worn out.

But, please do take wmproops advice and level the thermostat(must be extremely level). This is a very cheap possible fix. Let us know if it works.

generalservices · Jan 24, 2009, 07:40 PM

Hey guys!! Just to let you know I did check the gas valve ohms and it called for the anticipator to be set @4.4 Anyway my neighbor had a used Honeywell 7 day programmable the he din't like laying around so he gave it to me to try. I hooked it up at noon and guess what!! The furnace worked totally different! I was only there 1/2 day and it seemed to work as it should. I will be working a full day on Mon and give it a full day test. No one around here had a Pro 5000 so I'll wait till I get to the big city to pick one up. Thanks for all the help and have a good weekend. THANKS

mygirlsdad77 · Jan 25, 2009, 04:47 PM

Good to hear. If neighbor will let you keep thermostat, just use it. Your problem is solved, good job.

generalservices · Feb 1, 2009, 11:59 AM

To mygirlsdad, Guess what? Remember the Nordyne furnace? Well it worked for a week and now it's blowing thr circuit board fuse (3 amp). We, 2 different hvac guys and me have it narrowed down to this. When we unhook the green ground wire that comes from the circuit board that goes to the furnace ground, the unit runs OK. But if the ground is hooked up it blows the fuse. With the power on there is 5 volts coming from that ground wire. One prob on the wire and one on the furnace body. If the thermostat calls for heat, that same ground wire coming from the circuit board will register 24volts between the wire and furnace body. A new circuit board and a 24volt transformer have been replaced and still the same thing. All wires have been checked, rechecked, unhooked, tried this and that and are at a loss. WE will be having a electronics tech coming Monday to look at it to see if he can figure anything out. Anyone has any ideas let me know.

mygirlsdad77 · Feb 2, 2009, 04:47 PM

Can you post some pics of the ground wire that is causing the problem(preferably a good pic that shows were it hooks on both ends. I would guess that you have a problem with your low voltage wiring(a dead short of some sort).. Please let me know what the tech finds, I'm curious.