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Old 12-15-2012, 10:47 PM   #1
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Sears Heater system doesn't stop


I'm no expert but I'm handy enough to try to fix this myself or learn more about what the HVAC repair person will need to fix. I recently moved into an apartment in a house so I don't know the whole history but ...

I know that as of 2 weeks ago the unit was working for both AC and heating.

it's got ceiling vents in a single story house from the 40s in Texas west of San Antonio in Uvalde. The 82 y/o owner lives alone and has done nothing but ignore it for at least a decade. Recently we had 25 degree temps and no heat so I have decided to either fix it myself or pay someone to fix it since my apartment shares the heating system with the rest of the freezing house.

This is an ancient Sears heater/ac system that is a 240 V with what looks like 4 heating elements inside a water boiler system on the first floor with an access door and an access panel. (my internet connection is too slow for pictures.)
There are two black relays with ground wires branching off to the heating elements and also 2 wires from the thermostat. I didn't touch any wiring so it's all where it should be but that doesn't mean the relays are working or that the wiring is reliable since I could immediately see two crimps that were loose. At the point I investigated I couldn't get the fan to start no matter what I did. All the breakers were on and the boiler was radiating warmth but the fan blower would not run and the motor did not sound like it was humming.

the thermostat was labeled "1997" so I changed that out after turning off the breaker at the breaker box and the breaker for the motor.

The new thermostat is a White Rogers Heater/AC dual unit that had only one difference being the R wire was terminated on the RH screw. the yellow and white and green all went to their respective screw termination. I set the anticipator dial to the same setting. I believe this is a 4 wire, type 5 thermostat.

I turned the breakers back on and the elements began to hum as they heat the water and the motor pulley turned the belt and engaged the blower fan pulley (although the bearing is shot so the internal cooling fins on the drive shaft of the motor ping loudly against the housing when it slows down. this is a separate issue of finding a 1/2 hp 240v motor to replace this ancient Franklin Electric motor) Warm air and dust is blown through the vents but nothing I do to the thermostat will turn the motor off. I lower the temperature, I turn it to cool, I turn it off, and the motor continues to blow hot air through the vents.
The only thing I noticed is that I was using a lamp as light and when I turned the temperature up or down around the 75 degree mark, which was room temperature at the time, I could hear a click in the heater compartment around the relays and the lamp would flicker slightly like a drain was taking place and then brighten back to normal. It's the same as when you have a working thermostat and you lower the temperature and it clicks and the heater shuts down. I hear the click but the motor doesn't stop.
The only way to turn the blower fan motor off is to flip the breaker switch on the heater panel that is labeled "For motor protection only"
This may have been how the owner has been turning the heater on all this time.

My tools are limited and even if I recrimped all the female blade terminals at the end of the ground wires I would still need guidance to test the relays. Should I just test for continuity? I could see some corrosion on the crimps so it could easily be a faulty wiring connection that has cut the thermostat out of the loop and shorted the system.

I will replace the motor but that's not going to solve the thermostat issue.

When I placed the compartment panel back over the assembly and flipped the motor breaker back on nothing happened so right now I'm back to square one. I didn't pinch any wires but maybe the panel is moving the wires so they are disconnecting.

any advice?

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Old 12-16-2012, 02:10 AM   #2
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Sears Heater system doesn't stop


I would say you renting doesn't give you authority to do repairs.

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Old 12-16-2012, 05:29 AM   #3
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Sears Heater system doesn't stop


Sounds more like you have an air handler and not a boiler.

It probably wasn't the thermostat. Relays/sequencers are probably sticking, or you didn't give then enough time to open.

Need a multimeter to test what is not working like it should.
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Old 12-16-2012, 06:33 AM   #4
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Sears Heater system doesn't stop


Have to agree with Bob. It's not your property so don't mess with it. The landlord HAS TO provide heat so if it's not working he is required by law to get it fixed.
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Old 12-16-2012, 12:29 PM   #5
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Sears Heater system doesn't stop


You're right, it is an air handler. I call it a boiler because of the water or steam pipes I see running next to the unit but that's the boiler part of the indirect coil air handler. it has the Squirrel cage centrifugal blower fan. Amazingly it still produces heat and air conditioning so my immediate goal is to get the thermostat back in the loop. I just remembered that a few days before the blower started working non stop the cycles got very short. It would cycle on for a minute and then off. on and off and on and off. then it quit cycling and just stayed on until we turned off the breaker.

I think when I turn the thermostat off and the motor is still running after ten minutes then it's safe to say the thermostat isn't working.

It sounds like the most I can do is test the relays for a short circuit and then tighten/clean the crimps on the wires leading from the thermostat to the transformer and the relays. And if I can find the filter I'm sure that is due for a change.
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Old 12-16-2012, 01:24 PM   #6
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Sears Heater system doesn't stop


Probably a fan relay or sequencer stuck.

If your have a hydro coil in the air handler. that probably provides heat for less money then the expensive electric strip heaters do.
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Old 12-22-2012, 05:24 PM   #7
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Sears Heater system doesn't stop


it's been a mystery trying to figure this out but all the repair shops are booked until after Christmas so it didn't hurt to experiment with solutions. trouble is that closest parts dealer is 140 mile round trip. So, replacing the sequencer and the heat limiter isn't possible until they open next week.
At one point the air conditioner came of full blast and I have no explanation for that since the thermostat isn't controlling anything. the A/C control wire to the house is falling apart.

I find no 24v coming from the transformer so the thermostat isn't even getting power right now. Basically the right side heating elements aren't engaging on demand. And as soon as I turn the motor breaker on all the timing elements shut off and I get cold air. if I turn it back off the elements begin to warm up. If I leave the air conditioner breaker on then it eventually kicks in. It's already 50 degrees in the house but for some reason the A/C tries to make it colder and the thermostat only goes down to 60.

I'll be replacing the sequencer and the single throw limiters and the transformer if I can find them at Graingers in San Antonio. At least the parts will be new if a service tech ever arrives to troubleshoot the problem. I suspect he'll say the unit is unserviceable.
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Old 12-27-2012, 10:14 PM   #8
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Sears Heater system doesn't stop


Since no repairman can help me for another week I'm still trying to solve this air handler. I replaced the transformer and got the sequencer to work again but the puzzle is that the blower motor will not turn off once the sequencer is opened (shuts off). The thermostat is getting 24v but it can't turn the fan off. So, the fan relay is probably stuck closed but I'm not sure what the replacement part will be.

But the real problem is that even with 24v going through the thermostat, the fan blowing AND 120 v going to each timing coil and heating element terminal and the sequencer's 4 terminals closed, NO HOT AIR IS BEING PRODUCED. I could live with manually shutting the blower off but there is no heat. As soon as the blower comes on all the heat disappears. The A/C isn't coming on but neither is the heat. Only when I shut down the blower motor does something warm up inside the sheet metal compartment. It never gets hot but at least the metal warms up. 110v goes directly to the left side terminals that a schematic tells me is the timing coils. Are they the same thing as the heating terminals? THe left side terminals come directly from the main power jumper terminals. The right side terminals are jumped through the sequencer and only direct 110v to those right side terminals when 24 v is channeled through the bottom terminals. But that only happens when I turn the thermostat on AND manually flip the breaker to the motor. But as I said, when I do that the power goes to the terminals but there's no heat. It's like I'm visually seeing things work but the end result is 50 degree wind chill through the vents.

SO, let's figure I'll fix or replace the fan relay if I can find a replacement (it's that black box next to the transformer in the picture). Are the heating elements themselves burned out? There are 5 heating elements total but the top ones are not connected since the sequencer only has 4 terminals. Could all 4 be burned out? The transformer, fan relay, limiter switch, thermostat, sequencer and every heating element all failed in the same week? Sears service dept gave me an appointment for one week from now with 30 degree nights predicted so I'm prepared to drive to the big city to buy a fan relay and heating elements and motor...but if anyone has any suggestions or even a diagram of what I'm looking at then I would be grateful. For instance, is the heating element warming up a container of water? OR does air blow over the elements and that's all it does. What else needs to be serviced in the heating part of this air handler?
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Old 12-28-2012, 02:16 PM   #9
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Sears Heater system doesn't stop


Check for 240 volts across the sequencer when the stat is calling for heat. And when you have the fan turned off.
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Old 12-28-2012, 04:09 PM   #10
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Sears Heater system doesn't stop


I was getting 118v across the sequencer and was puzzled until I took the heating elements out and they were all burnt out except for the bottom one, which has a big kink in it, and the top one which was a spare. So, the coil itself was broken on three of them. The warmth I felt was the one working element turning on. I'm not sure why it was warming up with the stat turned off but that's another problem. the hunt begins for replacement elements.
I tried to shortcut the coil from one terminal to another and it worked for a few minutes until it burned out also. For that minute I did get 240 across the sequencer...so at least that works.

The fan relay still doesn't stop the fan even though I took that apart and filed/polished the contacts. The relay clicks when I turn the stat fan switch on and off but the fan never stops. The relay has one wire joined with the green wire from the stat and another wire joined with the A/C control wire. Even when I turn the A/C breaker off the fan keeps going. and I bang on the relay with a mallet and it won't shut off.

My advice is when you live this far from a parts supplier then build a fireplace.

Update: No one in my part of Texas has this part so if anyone has a parts supplier who deals with antique Sears Heating systems then let me know. I need three of them. The unit model # is 493.58703 but I don't have a part number for the heating element. It's 5000w 240V. It was a central air conditioning unit but that's been replaced by one that sits outside. The heating parts are original. This might be the end of the line. I already tried to stretch the coil and it just breaks and crumbles from age. Solder will melt again when it gets hot. Any other ideas to bridge the break in the slinky element?
another model number is: heating furnace 126646.

This evening I replaced the sequencer and a limiter sensor and then stretched the heating element to reach the terminals but it won't last because the coil is aged and brittle and it decreases the actual surface area of the coil itself. But it works and there is emergency central heating now. SO the only puzzle I can't solve is why the fan won't stop. The routing is a 120v goes into the motor breaker switch and exits into the + red wire of the motor. The - black motor lead branches off with one branch going to an upper limit sensor and the other branch going to the fan relay. Both of these branches have 120v present when the breaker to the whole system is on. So obviously the moment I switch the breaker of the motor back on then it power on and turns no matter if the stat is switched off or the fan is switched to auto. The other top lead to the relay is a 120v from the main terminal screw cluster. One bottom lead from the relay joins with the green wire from the thermostat that's in the G terminal. Switching the fan switch on the stat makes a clicking in the relay but nothing happens to the fan. And the other lead joins with the A/C control wires.

I suspect someone hardwired the motor to stay on because a sensor or relay broke but why would they hard wire it through a limiter sensor? A new fan relay would help but I'm hunting for that now.

Last edited by oggy bleacher; 12-28-2012 at 08:12 PM.
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Old 12-28-2012, 06:11 PM   #11
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Sears Heater system doesn't stop


A standard restring kit will probably work.
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Old 12-28-2012, 07:14 PM   #12
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Sears Heater system doesn't stop


that looks like a good boat anchor....... i would not invest a lot of money in that baby
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Old 12-28-2012, 07:21 PM   #13
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Sears Heater system doesn't stop


well its very nice that beenthere has spent some time helping you with this diy project...but I have to agree with carmon don't spend thay much time or money on that unit....he called it a boat anchor i won't even go that far...sorry ben sr
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Old 12-28-2012, 09:27 PM   #14
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Sears Heater system doesn't stop


Yes, that restring kit looks like what I need. I asked at Ace hardware, Graingers and another electric supply store and none suggested that item but I suspected it existed. Only I didn't know what it would be called.
My budget on this project was around $200.
$34 new thermostat
$40 new transformer
$40 sequencer and limit sensor
$8 x 4 restring kits = $40*

IF I can find the fan relay then the only thing left is an HVAC class to teach me how to wire it all together.

Oh, I forgot the $150 to replace the motor. Shoot. I'm going to be over budget. It's a $300 job in parts alone. Labor doesn't count since I am learning everything from you all.

* probably $20 each so $80 total.

Last edited by oggy bleacher; 12-28-2012 at 10:39 PM.
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Old 12-28-2012, 09:29 PM   #15
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Sears Heater system doesn't stop


well good luck ...... its a piece of crap that you should send to the grave yard...... we will however help you fix the pos in any way we can ....

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