Oil Furnace Troubleshooting
I have a Thermopride OL5-85 oil furnace that is running periodically but is shutting off prematurely well before reaching the desired heat level. The thermostat appears to be ok and indicates that it is calling for heat. I chased the thermostat side of things a bit and found: - The blower does not come on when the fan switch is set to on. - When the furnace is not operating there is not 24V available at the R/R1 terminal thus jumpering to W or G has no effect. The furnace and blower will run one or two times an hour for about 5-10 minutes. While running: - 24V is available between the transformer/relay (I'm not sure which this is) terminals to which the red and white thermostat wires lead. - The blower is running... air flow from the registers may be slightly less than usual? I don't see anything that would suggest any problems with the blower. - For the first several minutes the fan limit switch seems to hang around 120 or so. At some point, it starts to rise rather quickly and the furnace shuts off when the upper limit of 200 or so is reached. When the furnace shuts off, the blower shuts off as well. After a delay of 15-30 minutes, the furnace comes back on and runs through the same cycle again. Questions: 1) Is my assumption correct that there should always be 24V available at the R/R1 terminal of the thermostat? 2) Any idea what the problem might be? 3) The fan/limit switch has an auto/manual selector. Switching between those doesn't result in any obvious difference. What does that selector do and how is it used? Thank you!! It sounds like a wiring problem. If I had to guess, it sounds like the power to the fan/limit control is attached to the wrong terminal. The fan should not stop until the lower limit of the fan/limit control is reached, period. The burner will have no power (and no 24 volts to the thermostat) when the high limit is open. Setting the fan to manual with the button on the fan/limit should start the fan no matter what. You didn't say if there is air conditioning on this unit but I will assume NOT. The terminal on the bottom of the fan/limit should be hot all the time. There should be a jumper factory installed in it between fan and limit. The wire at the top on the fan side should go to the blower motor. The wire on the top on the limit side should go to the burner. The wiring may be wrong in the junction box oin the furnace burner cabinet. Check this stuff out and post back. Ken Thanks Ken! I'm wondering if I might have two problems? I did have a pro HVAC guy come wire up the furnace side of a new thermostat pretty recently and it's very likely I never tried the fan position on the thermostat until now. But the inability of the furnace to keep up with the heat demand is a new thing... unless it's just cold enough now to make it noticable. I should have mentioned that there's both an air conditioner and humidifier in the wiring mix. I put a few wiring pictures here. Just double-checking: - The wire labeled from humidifier leads to a transformer on the side of the junction box. - The from air conditioner and from thermostat wires lead to what I assume is a combination transformer and relay? The posts are labeled with typical letters: W is top left, R is bottom left. - The separate ?transformer? mounted below (which leads to the burner) is a step-up transformer? I've know there's 10,000-14,000V in there somewhere and have been duly careful... just would like to know exactly where Thanks again! I'll go check that wiring now... Everything seems to be wired right. I would of wired it with out the relay from the burner... Use the unused wire from the t-stat for RH. From what I can see seems like the fan control are set too close?? Does the burner stay on the whole time when there is a call of heat? When you said air flow is less.. How's the filter? Fan belt? Blower cage isn't plugged up w/ dirt? Lets handle one thing at a time and we can get this worked out. On the picture of yout fan control, The blue wire is generally the fan wire, that looks right. But the red wire is generally the limit wire and the black is the line wire. They are reversed. If they are not wired correctly in the box with the fan center on it, you will have the problem you described where the fan stops on high limit activation. It is what I suggested you look for in my last post. You need to check that out first. It may have happened when the a/c was installed if that was recently but first thing is to get the automatic operation of the fan squared away. Then on to the rest of it. If you have a tattle lite tester or a volt meter I can tell you check it easily. When the high limit is open and the control reads that the temp is at high limit. Check to see if the black or red wire at the fan control has voltage. If it is the red you are OK. If it is the black, they are reversed. Let me know and we will proceed. Ken A longer reply to Jay's questions was just lost to the bitstream... Short version is this.. everything is very clean, belt isn't slipping or showing signs of excessive heat. An aside: I have another, slightly larger version of this same furnace that heats the other side of the house. One notable difference I've found between that one and this one is that, on the one that works, I get 24V between the RW or RG terminals of the transformer mounted on the front of the junction box all the time. I don't understand this well enough to know if the reason I'm not getting that on the one that isn't working is related to the high limit being activated. I confirmed that with the fan selector at the thermostat set to on, and the limit selector in either the manual or auto position, the fan does not turn on. Ken, I'm headed back downstairs with the multimeter in hand and will let you know what I find. Thanks much for the help! - Mark Im with Ken here.That fan limit dont look set or wired right. 200 limit and fan on 110o off 95o. Will that tan pin turn the blower on for you there?I also see all the wire schematic there so check them out. Dont like that burn and blow back that it looks like on the door to the inside of the furnace. Looks like over heat and not the right draft there on the burner. Might check that transformer there and see if you have 24 V off it. ED ok, (I haven't touched any of this, btw, it was done by some HVAC pros and has been this way for years).... EXCEPT, I moved and put in a new thermostat a couple months ago. I wired the thermostat side and paid a HVAC guy to come wire the furnace side. Ken's test: when the high limit is activated there is line voltage between the red wire and ground only. A closer look at the fan limit controls: Off is at 100, On is at 130, limit is 200. I shut the furnace off for awhile to let it get much cooler than usual and then paid close attention to this cycle: When turned back on the burner came on, limit was less than 130 and the fan did not come on. The fan came on when the temp reached 130 and both stayed on for 10 minutes or so. Then, the fan shut off. With the fan off, the temp started climbing. When the temp got to 200 the high limit was activated and the burner shut off. The temp was above 130 when the fan shut off. Shouldn't the burner have shut off and the fan stayed on? What is it that triggers when the burner is supposed to shut off? The thermostat was/is calling for heat the whole time since it's set for 80 and the room it's in is in the high 50s. Thanks again! (Learning as we go...) - Mark Will the fan run if you push that button there or set the fan on down to 110o. Did you check the wire like Ken said there. if the blower dont come on till 130o it can go an hit 200 before the blower can get the hot air out.If the blower goes off again and it goes to limit check the blower motor out and see if its ok. ED Yeah, sounds like the motor is cutting out on your.. The burner is then staying on till hit the high limit. Take your meter to see if you are still getting 110v to the motor when it's not running. Glad to hear the wiring s correct so far. I think the next thing in the sequence is to check the blower motor. Open the fan compartment and be careful of the belt and chech the temperature of the back of the blower motor. If it is too hot to hold your hand on, it is probably defective. It would be going off on high temp. One reason other than defective motor would be if the motor pulley is adjustable and is closed up too far. Sometimes they do that on their own if a set screw comes loose. If the motor is overheated and no other reason is found, replace the motor, and because a/c was added, make sure to get at least 1/3 hp. Let us know if you have any other questions pertaining to this issue. And don't bother trying to figure out the reason why the fan won't work from the thermostat or the manual switch until you get that motor problem fixed. Ken I cannot manually turn the fan/blower on regardless of the positions on the fan limit switch or auto/on on the thermostat. I just realized I gave you guys some bad information... the terminals are marked differently between my two furnaces. Referring back to the pictures the: the upper left terminal is marked C, below that is G and bottom left is R. Right side top is Y and bottom (with nothing hooked to it) is W. So, from my thermostat, R is going to R on the terminal. W is pigtailed to a white wire that leads to that lower separate ?transformer? which then goes to the burner controller. Sorry about the confusion... Ed, we might have cross-posted: Ken's test showed line voltage between red and ground, so it sounds like that's ok. - Mark Set that fan on down as low as it will go let see if the blower will stay on??????? prove this first Like Ken said have to find out if the motor is good here first. for the tstat R is power W is heat G is fan Y is compressor C is common need this it the tstat dont have battries ED Just checked, when the blower stops the blower motor is too hot to touch. Sounds like the likely culprit. Thanks folks!! - Mark Did you check the pully like Ken has mention about? Does the blower and/or motor has oil port? Originally Posted by Ed Imeduc Set that fan on down as low as it will go let see if the blower will stay on??????? Ed, I don't mean to be dense here, but I'm not sure what you're suggesting? What is it I should set? I could set the temp very low and run the A/C to prove the blower works... then see if the motor heats up and stops. Is that what you mean? - Mark Just make the blower motor stay on and run have to find out if its ok you can go to AC if you want. also on the dial there push the fan on down lowLike to find out if the fan limit will turn it on there at the furnace also. ED ...on the dial there push the fan on down lowLike Ok, I get it... you mean turn that fan limiter dial that says Do not turn on it. Checked the pulley and belt. Belt is not tight at all. The belt has 1 1/2 of play or so (but I didn't notice any slipping while running). The pulley turns easily, and has a little bit of back/forth play 1/16-1/8 or so. But there's no wobble and raceway/bearings are sound. There's a label that says to lubricate yearly with 30 drops of 10 weight motor oil but I don't see an oil port anywhere. Also, there's a small canteen shaped thing up on top of the motor that I don't recognize with a couple leads going to it. - Mark If I turn the fan limiter dial back down, after the high limit is activated, the burner immediately comes back on. The blower does not. The fact that the blower motor is so hot is very suspcious. I'm thinking that if I shut the heat off and let everything cool down, I should then be able to check to see if my thermostat fan switch works. One question, what signals the burner to shut off? Is there a wiring mistake that would result in the blower being shut off instead of the burner? Thanks again! - Mark There is a high-temp cutout inside the blower motor that is shutting it down. You can checkout the manual fan operation after letting the motor cool off for a couple of hours. There is no wiring mistake. We covered that already. The burner is stopped by the high limit. The fan should not stop until the temperature drops below the lowest tab on the fan/limit dial. Or if you have it on manual from the thermostat fan switch or the manual button on the fan/limit control it will never ever stop. I would say that motor is toast. Ken When you look at the limt/control. The wire from the right hand side is for the burner, and the left is for the blower. The lower one is feeding power to the control. So when the limit has reach 200, it breaks the power feeding the burner. If the blower motor was working right, the blower will stay on the whole time if the limit kicks in to cool down the heat exchanger.. When the temps drop below the 200, the the burner will fire up again. So right now, get a new blower motor on.. You may have to wait till Monday.... I know alot of home centers don't have motors.. I know Fleet Farm has them. I'm convinced! I just ran the A/C with a low temp setting and got the same result. While the thermostat was still calling for cool the blower motor heated up and stopped. So, what information do I need to be able to find an appropriate replacement motor? What a great resource this place is! Thanks again for all of the help. - Mark Like I said in my last post, You may not find a motor at a home center.. (Our store HD don't have them or Mendards) I have seem them at Farm stores like Fleet Farm, or Farm Fleet.. Grainger may not be open on Sundays... Or you can try your hardware store.. Other wise look in the yellow pages and see if you have a motor shop in your area.. They may sell you one after hours.? Thanks Jay. What I meant is that I'm not sure what to ask for. It's a 1/3hp motor. Do I need to know the shaft length, or how the pulley attaches, or rpms, etc? Figured I'd head to Grainger's on Monday. Did a little more reading. Seems like that canteen shaped thing on top of the motor is likely a run capacitor or start capacitor. One site suggested that a motor that fails with smell/smoke is done. But one that fails just by getting hot may just have a bad run capacitor. Is that something I should try to test before replacing the motor? Just bring in the old motor in with you.. I would up it up to 1/2 horse since you got A/C. Also, when you get the new motor, ask the guy to show you oil the motor if it has it. While you're at it.. Get a new belt.. Just hate to see you w/ out heat in Jan when the belt breaks! I'm not completely sure but belt drive motors usually use start capacitors and direct drive motors use run capacitors. It won't hurt to check the capacitor but the motor has been heated up pretty high and the overload has been tripping for some time. That tends to weaken the overload switch and even with a different capacitor, you could still have a problematic motor. It is a very common motor. See what horsepower yours is now but on a furnace that small I would go with 1/3 hp. 1725 rpm 48 frame 1/2 shaft. It will most likely be reversible but make sure it is because murphy's law dictates the installation of non-reversible motors. 6K778 should be your best bet at Grainger. You did a fine job of troubleshooting the unit and if you take your time on the motor replacement, you will have as good of a job as anyone could do. Don't tighten the belt too much. It really does not get made as tight as you may think. Take Jays advice and get a new belt while you are out. Ken Wow Ken, THANKS! I was just looking through five pages of motors at Grainger's site trying to figure out the difference between the $60 motors and the $200 motors. You've saved me a bunch of time... 6K778 doesn't show a capacitor though... I was only looking at those that did? Under the do it once, do it right theory, I'm tempted to just replace the motor, capacitor and belt and be done with it. - Mark It is up to you but I don't use the capacitor start motors anyway. They may have their benefits but they also cost twice as much. Use your judgement and let us know how you make out. Ken Just some feedback: the new blower motor and belt is in and this little part of the world is warm again. Thanks to everyone for the help! - Mark Glad to see you're up and running! How did the blower itself look? Was it clean? Dirty blower leads to less air flow.
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