Heating, Air Conditioning, Fridge, HVAC/electric furnace
QUESTION: Sears model 867.587240. Furnace is 33 years old without any problems. I would say it is used weekly, not daily, for 7months per year. I replaced the original thermostat (Sears #387.914901) with Honeywell RTH2300.(The thermostat has a red and a white wire only). Do not know if that is relevant to problem or not,but after installation of thermostat the furnace fan will not shut off. I did not discover this for two weeks as we left for vacation and its when we returned that I discovered it. Subsequently I have tried everything to turn fan off. Fan stays on even when thermostat has been removed.
I replaced the fan relay (part# 604199)but that did not solve my problem. The only way I can shut off fan is at the fuse panel. When I trip the fuse panel on, the furnace fan starts immediately. There is no delay as when controlled by thermostat. I do not think my problem is thermostat related, but that is why I am asking for help. The furnace does heat when called to do so. Otherwise it just blows cool air. By chance I might have a faulty new relay but again I do not think that is the answer.
Without your help, my next thought is limit switch. There are (5) 160deg limit switches. This seems to be an expensive optionx5 since I would not know which one to start with. Hopefully I have given you enough details that you can help me. Thank you Pat
ANSWER: Hi Pat, Let's start with the basics. The red wire should land on the R terminal and the white wire should land on the W terminal. Make sure the switch on the stat is set to auto. On the back of the stat you will see two jumpers, the one on the left should be set to HE.
I have never seen a furnace with 5 limits on it. Can you send me a picture?
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QUESTION: Jim thank you for your rapid response. First photo shows wiring with 6 limit switches. My model furnace only has 5 as specified on parts page. I would have sent another picture or two but this web site limits me to 2.
Second photo is parts diagram looking at part 43. this part is listed as [Switch,Limit 160degF (5req)].
I don't know if I previously mentioned that fan runs regardless if thermostat is hooked up or not. When I switched power on to furnace and blower came on I tried everything I could think of to get fan off. This includes moving switches on/off/auto etc. I also set thermostat up and down and noticed that when required furnace would heat and when not required it would blow cool air. This is Heat only, no AC. I also while fan was running took thermostat off wall (fan continued to run) put old thermostat on wall (fan still ran) touched R wire to white wire etc and fan still ran. Hope these details will help and again I appreciate your time.. Pat
ANSWER: Hi Pat, Thanks for the wiring diagram. The limits that you are pointing to are the overloads. When the amps get to high they heat up and open, when they cool down they close. This is just a safety to protect the heating elements.
The problem you are having is in the sequencers. There are four of these on the drawing. Go to the drawing and find the blower motor. Find blue wire that is marked M HI and trace it back to the first and third sequencers. One of those contacts is stuck close. If you have a volt meter you can omh them out to see which one it is.
You could tap them with a screwdriver to see if it would pop loose. Most likely you will have to replace it.
Let me know if you have any other questions.
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QUESTION: ok Back at the project. had a bunch of snow to blow so its nice to get inside where its warm. (heating w/woodstove) I used Volt meter to best of my ability and wanted to share results. My mind interpets my readings as follows; readings w/1. are open switches. Readings w/.000 are closed switches. The other two readings .150 and .034 are something else and if I was an electrician I could tell you what those symbols are.
The pictures show the position of sequencers in furnace. I traced wires like you said and am pretty sure thatI got the correct ones. Wiring diadram shows BU wire changed to R after terminal block. These sequesters are between $100 and $160 as near as I can tell. It would be nice if you could help me identify which one might not be working. Its kind of expensive to go thru the process of elimination. Again I thank you for your help and research as you are making this project interesting for me and perhaps with your help I might win this battle. Pat
Pat, I think you will win this battle! Your pics make it easy for me. The top sequencer is the bad one. Your showing 0 on the contacts which means they are closed and 1 on the coil which means it has gone bad. Great job!
Go to www.hvacpartsoutlet.com. Search Rheem 42-23116-09.
Let me know what happens.