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My Monitor 441 was working just great last year, and hasn't hit a lick this year. I have taken the copper pipe loose from the inlet and verified that the unit is receiving excellent flow of kerosene from the tank outside. I pulled the screen out of the pump and it's clean as a whistle. I took the fuel pipe loose from the combustion chamber and checked it, no blockage. I checked the resistance across the solenoid, I'm reading about 50 ohms. The service manual says it should read 565 ohms. So I checked the solenoid on the old 441 we have for parts, and it reads 50 ohms also. So I figured either the manual is wrong or I can't read a VOM. I took the pump apart and checked to be sure the needle valve wasn't stuck, and everything in there appears to be fine. So I took the electrical connections off the solenoid and hooked my VOM directly to the wires, and set it to read 250 VAC. Then I plugged the unit in and ran it through its paces, and never saw any voltage to the solenoid at all. Any idea what might be causing this?
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Was the solenoid making any noise or was it completely dead? On Low or Low-Med you should hear it thumping around 7 to 9 pulses per second. If you measured the solenoid resistance with the wires still connected you're also measuring the resistance of the diode connected across it. The voltage on the solenoid is a pulsing DC; it will cause the needle of an analog VOM to wiggle. Try measuring the AC and DC voltages across the appropriate legs of D2, the bridge rectifier that supplies the DC for the pump circuit. Don't forget the 2 Klixon switches under the top housing cover and the air pressure switch connected by a hose to the combustion blower are in series with that rectifier. -
I measured the resistance of the solenoid while it was disconnected and got 50 ohms. That was measuring across the terminals that the wires go on. It's not making any pulsing noise at all. I don't think there's any power going to the solenoid. I disconnected the wires from the solenoid and hooked my VOM to those wires and didn't notice any reading at all for the first 6 or 7 minutes. By then the unit was flashing the full burner status lights, which means it's out of kerosene.
Interesting that you mention the air pressure switch and the switches on the burn chamber cover. While trying to figure out what was wrong with it, and referring to the connection chart in the service manual, I noticed my unit is not wired like the manual says it should be. But the dang thing worked just fine last year, if quite a bit noisier than I would like.
Anyway, here's what's up with my wiring. If you look at Figure 7-1 Monitor 441, it shows J connector going down to the air pressure switch, then to the two overheat thermostats, then back to J. Mine goes from J, down to the air pressure switch, then to the fan thermostat. And the C connector goes to the two overheat thermostats on mine, when C should work the fan thermostat. Simple fix, right? Just swap the wires at the top, and connect them to the proper thermostats. Well, when I tried that, the fan came on as soon as I plugged the unit into the wall outlet. Resistance measurements on the thermostats while cold: overheat thermostats are closed, fan thermostat is open.Comment
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monitor
which fan came right on? there are two. the combustion blower is the FIRST and LAST fan to come on and shut down. The circulator comes on only when the plenum temperature rises to its set point.
the solenoid pump terminals has a current dropping resistor in series with one terminal. It is NOT a diode. So, if you are reading resistance you are also reading the resistor.
the solenoid pump has a modulated signal applied to it off its driver off the taisan pump controller. ac in dc out at a pulsating rate.
If you have no noise at all coming from the pump, either the controller is shot or the pump is shot. every unit is different. the last unit produced, the 2400, the controller is built right into the mother board circuitry.Comment
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It was the circulator fan, the big one in the black wire cage on the back. That was obviously wrong, so I put the wires back like they were.
I'm not getting any voltage at all from the DC side of the D2 bridge rectifier. Haven't checked the AC side yet.
Is there any possibility that the air pressure sensor could be keeping the unit from pumping kerosene? Since it's in the same circuit with the overheat sensors, I'm thinking it could be telling the processor that the unit is overheated or otherwise faulty. But I'm not getting any error codes. And if there was some reason the safety mechanisms wanted to shut down the unit, I wouldn't think the burner status would start up.Comment
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circuit chain
what you might do is apply a jumper from the 24 volt hot bypassing any variable devices like the air switch[normally open] klixon switches [plenum overloads] to the main relay on the board and see what happens. if the unit operates ok then its a process of elimination [each safety device]Comment
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You might want to check you larger black hose from the blower to the burner. I have seen them stopped up. Also check the 2 amp fuse on the heater. I have seen the 2 amp fuse blow and everything start up as normal until the pump comes on. Also on the 441 you shouldn't have a fuel pump control board. It should be built straight on to the board.Originally posted by HayZee518 View PostComment
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Try pulling the "J" connector off the PWB. Jumper the two "J" pins on the PWB and see if the pump works when the 441 starts up. If you're not seeing about 120 VDC on the DC terminals of D2, it's probably the air switch not working or its hose broken. You seem to have already checked out the Klixons.Attached FilesComment
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I jumpered the J terminals and the unit started pumping kerosene into a quart jar when the burner status light went on. I did that so I could see whether it was pumping. So it has to be the air pressure switch. I pulled the black rubber elbow pipe off, clean as a whistle. Ditto with the small rubber hose on the pressure switch. I don't have a manometer to check the switch, but resistance reading is open across the two outside terminals, which is where the wires are connected. The reading between the middle terminal and the terminal that faces the front is closed. I'm thinking that if I move the wire from the back terminal to the middle, the unit should fire up. But that's somewhat like putting a penny in the fuse box. I have a dead 441 that I can scalp parts from. I replaced the air pressure switch with the donor, and got no change. Still won't pump kerosene. So what is the air pressure switch reading that it doesn't like?Comment
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Okay I tried to take the rubber hose off the blower connection and discovered the blower motor casing is hot. The unit was awful loud last year and but it was working. I'm almost positive the bearing have seized up in the motor, and that's what the pressure switch is griping about. I'll replace the motor with the motor from the donor unit and I'm pretty sure that's gonna fix the problem.
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motor
that pretty much sounds like the cause of the air proving switch not closing. its sort of like a sail switch but this one operates off a rubber diaphragm.
the motor can be taken apart after grinding down the three rivets. the bearings are a 7mm bore 608Z sealed bearings. same bearings used on inline skate axles.Comment
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Another check of the air proving switch is to remove it from the Monitor and gently blow into the "Hi" hose nipple. You should hear the microswitch click. If you put your ohmmeter probes across the outside terminals, it should show 0 ohms when you do this. The operating pressure is only about 0.5"WC or around 0.02 psi.
The blower housing assembly can be removed by removing the front grille, control panel, top panel, inner heat shield, and printed wiring board (PWB) mounting panel. Tools required are a Philips screwdriver and a stubby Philips screwdriver for the screws on the rear of the Monitor heater near the wall. The heater doesn't need to be removed from its normal position.
The housing assembly can be disassembled with a Philips screwdriver, a 13mm socket for the left-hand nut securing the first-stage rotor, and a 2.5mm Allen wrench for the set-screw securing the second-stage rotor.
The motor bearings are type 608 and should be shielded or sealed. Use at least ABEC Class 3 quality. McMaster-Carr 6661K82 are ABEC-1, but McM-C claims they are made to class 3 tolerances.
There is an O-ring on the solenoid piston that acts as a bumper to deaden the shock when the piston is retracted. It sits on a groove on the end of the piston. It is 7mm ID, 11mm OD, 2mm thick, black rubber. McM-C 9262K167 works fine. If the O-ring breaks down and falls off, the piston will retract that much further, and the damper will close slightly more.Comment
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I replaced the fan with the donor fan and the problem is resolved. I want to personally thank every person who took the time to share their insights and suggestions. You folks rock!
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