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I have an older unit that doesn’t have a control panel. It works with a sequencer. (Coleman 3500A816) Is it possible to wire it so that only the blower is called for on and not the heat?
Electric Furnace Wiring Diagram
Unfortunately, you have an oddity among electric furnaces in that your furnace controls its fan autonomously using sequencer relays, just like a gas furnace does with its thermostat/fan limiter. As a result, your electric oven doesn’t natively support the G chord. Fortunately, merging isn’t too difficult.
Wiring Your Radiant System
In the right place. In your case, you (or your HVAC tech of choice if you’re not comfortable replacing your furnace) should:
Once you have everything hooked up, you can turn the system back on and perform test operation with both the thermostat fan switch in AUTO and the thermostat fan switch ON, then enjoy your upgraded furnace!
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Visually Inspecting Wiring And Terminals Of Electric Furnace
What is an isolation relay or isolation switch used in heating or cooling systems and how is the relay connected? Isolation switches allow a low voltage circuit (such as 24VAC) for a thermostat to control high voltage equipment such as an electric heater and fan in an electric furnace.
This series of articles describes the wiring and installation of HVACR controls in detail and answers most questions about central heating system troubleshooting, inspection, diagnosis, and repair. We explain how to inspect, troubleshoot, and repair heating and air conditioning systems to inform homeowners, buyers, and home inspectors about common heating system failures.
We also provide a list of articles for this topic, or you can try the search at the top or bottom of the page as a quick way to find the information you need.
Connecting isolation relay on electric furnace Q: Connecting isolation relay on my electric furnace heating system
Wilbo666 / 2jz Ge Jzs147 Engine Wiring
I have an old electric furnace with heat and ac. I replaced the sequencer last year and the fan isolation relay last week. The wiring was suspect prior to the repair, I had to re-wire the 24 volt wires.
The only wire I’m thinking of now is the 240V wire from the heat sequencer to the isolation relay. The only problem I have is: only the high speed fan works. The low speed fan does not work when the heat is on, it continues to work as a high speed fan. It is an automatic fan and the fan is on. What is the proper wiring from the sequencer to the fan isolation relay to have a low speed fan for heat? I have high speed ac and fan as wired.
Bob, sorry for being less than helpful, but I think it is necessary, given the risks involved, to identify the brand and model of the furnace and then obtain the wiring diagram. If you have that, we need to identify the isolation relay terminals so we can specify the wiring.
Above and at the top of the page I show two white Rodgers isolation switch control relays; Second is assuming you have an isolation switch.
Figure 1 4 X . Practical Wiring Diagram
Thanks….I have a wiring diagram for the original furnace (1980 Vesco era). The unit was retrofitted with train ac in 1998 so the wiring must have been modified at that time. The original diagram only had the high speed connected to a switch, no isolation relay, and only the red and white wires at the thermostat. The isolation relay is a 91-132006-13302 with a pair of 24v terminals and two 240v switch terminals, the 240 connected to the bottom of the first switch with a high speed wire connected to the top.
The low speed wire is connected to wire 240 from the second switch to the second switch’s center post on top of the sequencer bag. This is as close as I can describe since the unit was retrofitted.
For other readers: An isolation relay is simply an electrical control that separates different voltages in an HVACR application, so that, for example, a 24 VAC thermostat can control cooling or heating equipment powered by 120 VAC or 240 VAC. Some isolation relays also support multiple switching, such as multi-speed fans.
Do you find that the fan is a model capable of multiple speeds, but the controller is only designed for one speed? If so, you may be able to wire the existing fan to a switch to manually switch between the two fan speeds, by adding an on switch.
Goodman Aruf25b14 2 Ton Standard Multi Positional Air Handler
I found these White Rodgers 1F90 / 1F97 Isolation Relay Wiring Diagrams that may help. Click on any image to enlarge:
I don’t know much about White Rodgers isolation relays, but if it helps with the fan speed issue, Honeywell’s R8285 is sold in different models that support only 1 vs multiple fan speeds. Those instructions also show the location and wiring for the isolation relay. When running a 2-speed fan with this control, the fan runs at a slower speed until the heat is called for, then the fan speeds up.
This shows the relay circuit I have. My fan has a multi speed motor with 3 speeds, of which I use two. I’ll study the link above and see if I can figure out how to run the low speed for the summer. As stated in my previous message, I am currently linked, this link should allow me to determine if I can change it. I’ll let you know after studying it.
Mod Response: The article shows a 12 volt relay (or other voltage such as 24VAC in some systems) used to switch high voltage circuits. User must identify each terminal for proper wiring; Usually they are stamped or marked on the relay housing:
Ambu Book On Wiring Diagrams 1917 1918 1919 (now Includes Later Posts By Members Re R Bosch, American Tech 1922 And Standard Eng 1921)
Reader follow-up: White and green thermostat wire not working as expected: why does the heat not turn on the low speed blower but leaves the high speed blower on.
Finally solving the isolation relay/fan speed problem. After reviewing the isolation relay connections above, I can confirm that my heating and cooling relays are properly connected to the terminals.
After confirming this, I tested the thermostat wiring again to see why the heat would not turn on the low speed fan but leave the high speed blower on.
I discovered to my surprise, that the thermostat was heating the green wire on the fan at the same time it was heating the white heat wire. (I thought the hot white wire would leave the green cold and make the sequencer fan run at low speed.)
What All Those Letters Mean On Your Thermostat’s Wiring
I also thought that if I use the fan on the thermostat the green will only get hot). When the green wire is hot during the heat cycle, the relay prevents the sequencer from connecting the hot wire to the low speed terminal. So problem solved, I know why low heat doesn’t activate.
My solution to this would be to add an additional isolation relay between the heat and the fan to get a low speed blower only on heat, a high speed blower on fan only, and a high speed blower on cold. Thanks for all your help. I added the conclusion to share how these isolation switches work and can help with troubleshooting.
It’s going well, Bob. This diagnosis will definitely help other readers working on thermostat or isolation relay wiring problems. Thank you so much for taking the time to follow up.
PS: Before adding another isolation relay, I would check that the white and green wires are not shorted anywhere along the way. Disconnect the wires at both ends of their circuit and then check for continuity. – Ed.
Wyze Thermostat No C Wire Nordyne Unit
My fans call the limit controls “push man” and an arrow, no white button, just an empty hole. What to do? I put the numbers back in their correct positions but the fan still stutters for a while then turns back on after turning off. I was lucky enough to replace my blower motor myself after ordering it online. No help from any man! My least concern was the fan limiter. Now after a month of heat I need help! Thanks
If your range control doesn’t have an actual operating button or push switch, this is a model that has omitted that feature. The switch will still operate automatically. Manual switch is optional, not mandatory.
Be careful not to mess with, force or bend the switch parts – this could make it unsafe.
There is an Olsen Ultramax furnace NG that clicks for 3 seconds for 4 seconds. I’ll replace the pilot assembly kit, hope that’s all. Runs a lot Already put in a new thermostat.
Page 38 Of Nordyne Furnace And M5s User Guide
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