King make up air unit
At work we have a 2.1 million BTU gas fired make-up unit for the spray booth, made by King Air Systems. It was installed in 1990 which makes it 23 years old now. It has served it's purpose quite well with but an occasional problem I've been able to troubleshoot and fix. One time the outside intake duct louver which are motor operated on a 45 second startup delay failed to open and that caused a failure to start up the unit.
I tracked that one down to a loose rod from the motor to the louvers, tightened and adjusted it and all was fine again.
I've been with the company 15 years, and every once in a while at random one of the cartridge fuses blows out, I believe it is 45 amps. Replacing the fuse all is well again for weeks, months or longer.
Now in the last year or so I noticed that fuse has not blown out any more, but a different issue took it's place, now again entirely at random with no cause or patetrn I have been able to notice, the unit will shut down, the panel alarm light turns on and I have to go out and press one of the reset buttons (there's 4 of them) only one seems to actually do anything when pressed.
It is the relay re2 on the wiring diagram I'll scan and post in a short while, and made by Honeywell.
What I was able to determine now after this happened several times in the last month, was that it has something to do with the winter heat circuit, the unit has a "summer" and a "winter" setting, and summer only runs the fan and blowers, winter runs those and controls the gas burners.
The unit will run without resetting that Honeywell if used on the summer mode, it won't run on the winter mode without pressing the reset in the unit.
The unit also has a Maxitrol series 44 amplifier, and a modulating valve that varies the gas flame according to temperatures inside and out, and what the thermostat is set to.
So I am able to narrow this down at least to one function of the unit but wondered if anyone might have ideas on this.
What I believe the problem could be, is either the relay is going bad from age (23 years) or some other problem is causing it to trip, my problem is I don't know how how to determine whether it is the relay or some other problem.
I'm the guy who normally maintains all of the machines, equipment, tools, lights, main compressor etc in the whole plant, as well as I take care of building related things like roof leaks, gutter ripped off in a storm, broken door lock, backed up urinal, leaking pipe, the air lines, dust collector, energy recovery air unit etc.
I almost always can repair fix or rebuild just about everything there, and sometimes that's a challenge because most of the machines were made in Germany, while others are 20, 30 years old and parts are hard to come by.
There's very little I haven't worked on there or been able to fix, the few times there were, such as a failure of the new electronic gas furnaces, or anything to do with electronic circuit boards, I can almost always track the trouble down to one or two causes or possibilities, and have the foreman either call for the parts or someone to come out.
In 15 years we've had to call someone out from the factory one time for a machine, and a few times for the electronic furnaces, I don't do circuit boards.
But this King unit is fairly complex and there's a lot of "possibles" for failures, and its worse when it's random and intermittant like this has been.
I'd like to at least be able to tell my foreman something like "this is where the fault is, here is the part you need to order, or you need to get someone in to replace this component"
I'd hate to guess or be wrong and tell him it's the relay, have them spend a lot of money on the part and then discover the relay wasn't the fault only the symptom and the problem is still there.
Wiring diagram, Re2 is circled on the lower left corner:
I notice one of the connections to re2 which has the reset button I have to use, goes to the flame sensing rod.
The diagram for the diagnostic light panel on the outside unit:
And lastly, the normal operation detailed:
lower left corner applies as the alarm light on the inside control box does light, it confirms my finding the issue is related to the heat (winter) circuit, and the alarm light according to this indicates a failure to ignite the burner condition and a lock-out. The sudden shutoff it seems will happen right about the time the main burner is expected to come on and light the "main burner" green light on the control box, but I think it has also happened at random during operation, not just then.
It ran all day fine no problem, and most of today and then cut out around 5 pm suddenly.
The unit is used at random times and is usually used for short times, followed by days or even weeks when it's not used at all, but once a year or so it is used for days at a time 8-10 hours a day.
I'm sensing this has something to do with the burner, failing to ignite and when it does it sometimes goes out, but whether it's that relay re2 or the flame sensor rod, or what I can't tell yet and I'm not sure how to narrow this down to a single component, so if anyone has ideas I'd like to hear them.
Well it does not show the internals to RE-02. Or give any specifics about the flame sensor rod.
If the flame sensor is a "thermocouple"...
Those create a small amount of electricity when a flame (pilot light) is present. But without any specifics for the part or relay, no telling how much electricity that should be putting out! So no way to measure it and know if it is good or bad.
Anyway it is common for those to go bad with age in furnaces. Might want to search google.com for the following words and see if you can find any troubleshooting info...
Also companies which manufacture things like this also publish "service manuals" (along with operation manuals and installation manuals). But they don't typically provide those to the customer unless you ask. So might want to ask for one. That should give testing and troubleshooting information. (Maybe on their web site?)
Also if this has a pilot light which is always on, you could peek inside and see if it is still lit.
The RE-02 has a plastic cover held in place with one screw, I have not looked inside, I might do that on a slow day, for all I know I might find an obvious problem right there.
I do know they can go bad, and the wire can also come loose too, there's vibration in the unit as it runs.
I did look in the peep hole last year while it was running to become familiar with how it should look, I didn't see anything unusual, anything loose, rusted, broken, the filters were clean, fuses all snug.
I'm guessing once it interrupts the current and causes that lockout, that's when the reset button has to be used, and it's in fact working properly and may not be the problem at all since it does immediately cycle to start up again.
That and the alarm indicating a flame out or no ignition condition, together does seem to point to that thermocouple/flame sensor rod.
The unit being from 1990 and not having any real electronic circuit board stuff in it, I think it's going to be a thermocouple that puts out the current to a sensor in that wiring diagram, I'll have to read it over again and see.
The pilot either turns off once the main burner is lit, or it turns off when the unit is shut down, either way I know there is no pilot flame on all the time, just when the unit is running.
The inside control box heat dial goes up to 90 degrees F it doesn't get hot enough to bake enamels on and the like, just to warm the spray booth's makeup air to replace what is exhausted out the filter wall.
I'll look into a service manual and the possibility of the thermocouple/flame rod in there when I get time and see what I can find out, thanks fo rthe input.
Yeah, that's got to be a thermocouple, in reading the material again it says:
"...flame rod detects pilot flame and ignition transformer drops out of electrical circuit"
The only way for that to happen is the flame rod either sends an electrical signal, or it has some kind of a spirit tube/diaphragm that does, but I put my money on the simpler and cheaper ordinary thermocouple sending an electrical current back that cuts that transformer out.
RE-02 is the flame safeguard relay and it powers ignition transformer TR-02 and pilot valve VG-01, both of those are shown in the wiring diagram near the right lower corner.
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