DIY Home Improvement Forum banner
1 - 17 of 17 Posts

· Registered
Joined
·
11 Posts
Discussion Starter · #1 ·
Hello- I believe I have a high limit switch on my eletric heating element that I need to replace. I have not been able to find an exact replacement for it based on the part numbers. This is from a 1990's westinghouse heating element. The switch is marked 402-1532 and L200-A9. I have found various L200 high limit switches, but nothing for "A9". I do not know if that part is important. I believe each one needs to support 5KW. Can anyone recommend a replacement that should work? Thanks!

Automotive tire Vehicle brake Auto part Machine Nut
 

· Registered
Joined
·
17,831 Posts
The 200 is the limit open temperature and that must match.
The characters after the - normally indicate how far the temperature has to drop before the limit closes again.
Its not critically important, but shouldn't be too low or it will reset too fast.

Normally, characters are numeric only, for example, 200-20 indicates it has to drop to 180F before the limit closes again. don't know what a9 indicates.

The issue is, using a limit that is not a direct approved replacement even if it is a good match could void safety certifications, causing problems with insurance, etc if something were to happen related to the electric furnace causing property damage.

Just to warn you, limits fail open only after opening and closing too many times.
You most likely have an underlying problem with the system - the most likely being low airflow*.

*Dirty blower wheel, plugged and/or filter too restrictive, oversized unit on undersized ducts, heating blower speed set too low, too many vents closed/blocked, etc.

So after the limit is changed, need to do further investigation to make sure it is getting proper airflow.

The wire and connector are also in poor repair, missing insulation -> must be fixed when replacing the limit.
 

· Registered
Joined
·
11 Posts
Discussion Starter · #3 ·
Ok. I get a 200 with the highest drop I can find before it kicks back in. I don't think it's actually been cycling anymore, however the old furnace did have restrictions. Before I replaced the furnace there were 3 separate zones and only one ran at a time. I changed it so the first two floor zones were always on. My calculations showed that it only had half the duct volume the furnace required with only one zone. I also reduced the propane furnace size from 120k btu to 80k btu. My feel is that there is corrosoin or a mechanical failure in the switch causing restistance. The switch itself heats up and goes from ambient to near 200 F in less than 5 seconds after turning on and none of the surrounding sheat metal really goes above 100 F.

Water Purple Petal Violet Pink
 

· Registered
Joined
·
17,831 Posts
Ok. I get a 200 with the highest drop I can find before it kicks back in. I don't think it's actually been cycling anymore, however the old furnace did have restrictions. Before I replaced the furnace there were 3 separate zones and only one ran at a time. I changed it so the first two floor zones were always on. My calculations showed that it only had half the duct volume the furnace required with only one zone. I also reduced the propane furnace size from 120k btu to 80k btu. My feel is that there is corrosoin or a mechanical failure in the switch causing restistance. The switch itself heats up and goes from ambient to near 200 F in less than 5 seconds after turning on and none of the surrounding sheat metal really goes above 100 F.

View attachment 728792
A bad electrical connection can cause the limit switch to get hot fast.
You may not need a new limit since it is cutting out at the right temperature and resetting.

Re-do the connection - replace the damaged section of wire with same gauge/temp rating and re-do the crimp connection.

If you have a clamp ammeter, check the amp draw on the wire after.

Are you saying the same system has a propane furnace too? How/where?

When system is zoned, the heat should be staged be it electric or propane - so it runs at reduced output when only one zone is on.
What size is the electric furnace? How many kw?
 

· Registered
Joined
·
11 Posts
Discussion Starter · #6 ·
Yeah, I tried to clean up the connection.The switch broke apart trying to unscrew the wire. It's an 80k btu propane furnace with 20kw electric. The furnace itself is a couple years old, however the eletric elements are about 30 years old. The elements are mounted above the furnace before the ac coil. The power company can turn off the electric any time they want so the propane is mostly for backup. I removed the zone dampers when the furnace was replaced, so not zoned anymore.
 

· Registered
Joined
·
17,831 Posts
Yeah, I tried to clean up the connection.The switch broke apart trying to unscrew the wire. It's an 80k btu propane furnace with 20kw electric. The furnace itself is a couple years old, however the eletric elements are about 30 years old. The elements are mounted above the furnace before the ac coil. The power company can turn off the electric any time they want so the propane is mostly for backup. I removed the zone dampers when the furnace was replaced, so not zoned anymore.
So you have a plenum heater.

Try to get the model number for the whole assembly (heater add on kit), then look up parts.

If the part is discontinued/obsolete with no oem replacement, would be looking at a l200 limit that fits that can take the current. (safety certs would be voided as i already mentioned)

One thing I wonder is how it is wired to turn on the fan - if it is just a single signal to G terminal on control board.
Most new furnaces use a very low speed in continuous fan mode from factory - low enough to cause serious overheating problems with the electric elements.
20kw will need at least 1000 cfm.
What is the full model number of the furnace?
 

· Registered
Joined
·
17,831 Posts
How is propane is for back up if electric is turned off by power company? Blower motor not spinning?
just curious how and where is this unusual set up located?
Likely meant electric heat is turned off - likely a double throw relay that diverts call for heat to plenum heater and when demand is high, it diverts it back to w terminal on the furnace to ease demand on the grid.

Could be a dual energy plan, get a special low electric rate in exchange for switching to fossil fuel in extremes when grid is maxed out.
 

· Registered
Joined
·
11 Posts
Discussion Starter · #10 ·
Likely meant electric heat is turned off - likely a double throw relay that diverts call for heat to plenum heater and when demand is high, it diverts it back to w terminal on the furnace to ease demand on the grid.

Could be a dual energy plan, get a special low electric rate in exchange for switching to fossil fuel in extremes when grid is maxed out.
This is correct.
 

· Registered
Joined
·
17,831 Posts
I ordered a l200 60 to try out. Only 2 of 4 coils are working currently. It's just keeping up at -15.
Please give full furnace model number and how plenum heater is wired in with furnace, with all the elements on you may have overheating and cycling on limit due to low fan speed - it sees G signal only as call for continuous fan.

To be honest you may not need all the elements working anyway. It is actually better to more closely match heating needs and not cycle as much.
 

· Registered
Joined
·
11 Posts
Discussion Starter · #13 ·
The furnace is a 92% Eff 80k BTU goodman upflow. My calculations said I could go with a 60k BTU, however the furnace installer talked me into going with the 80K since the old furnace was 120k. The plenum heater is a Westinghouse Model URZ36EA120 Style 3965A51G03. The wiring is not as clean as I'd like. I haven't spent any time trying to clean it up and understand what all the wires are doing. There is a switch that lets me switch to propane only or plenum heater as the primary with the propane as secondary. The plenum heater has two pairs of these contactors.
Circuit component Auto part Automotive lighting Electronic component Machine


One of the 4 has been disconnected since I bought the house, so it's only ever run on 3 of the 4 coils since I have moved in. I do not know why the one was disconnected. The only image I have handy of the wiring is thermal, so hard to see much other than it's a mess of wires.
Purple Rectangle Violet Automotive lighting Font


You can see 3 of the 4 coils functioning on the bottom left.
 

· Registered
Joined
·
17,831 Posts
What is the actual model number of the furnace?

How is the airflow when it is running all electric?
 

· Registered
Joined
·
17,831 Posts
I don't have the furnace model handy. Airflow seems fine. The installer did some testing with a manometer when he installed it and didn't say anything was out of the ordinary. All rooms heat fairly evenly.
In electric heat mode?
Some furnaces use the heating fan speed for continuous fan, others (mostly newer) much lower.

Is the air very hot in electric heat mode?

Will have to to do some testing with a thermometer and see what the furnace is doing in electric heat mode (if it just sees it as a call for continuous fan) after repair or this problem may recur. Normally, the limit should never trip, takes an initial problem to cause this.
 

· Registered
Joined
·
11 Posts
Discussion Starter · #17 ·
The new limit switch fixed the issue.I let the house drop to 55 so I could do long heat cycle on it. It did not kick out at all and the new switch did not get over 100 degrees externally. The coil on the new switch is also drawing about .5 amps less than the other three. It appears the contacts in the old switch were corroded and heating up. I'm going to order 3 more and replace the rest also.
Automotive tire Bumper Rim Automotive lighting Gas
 
1 - 17 of 17 Posts
Top