Training Tips for Winter

Unknown

on tips for winter in case you were attending Wetstock and missed it.

Unknown

Basic Troubleshooting Procedures II

IDENTIFYING THE SYSMPTOMS OF THE PROBLEM

When identifying the symptoms of the problem, attention should be directed toward defining the function of the electrical circuit/system. This often times is best done with first talking to the customer and working with them on the initial identity of the problem and some symptoms which may have led up to the problem. They may be able to point you to the exact point of failure. If possible you want to isolate the problem to a relatively small section of the circuit/system. A good circuit diagram and ladder diagram can be very helpful in doing this. Once you have islolated the problem a systematic check using the diagram should lead you to the problem.

Probably the single most important rule in troubleshooting is to change only one thing at a time in the circuit or system. Usually it is the failure of one component which stops the operation of the equipment. Be careful however when blown fuses or suspected shorts are involved, a shorted component can damage some other part of the circuit (example a shorted gas valve can also burn out a transformer, you change the transformer and flip the switch and burn out another transformer). Learning how to find shorts using an ohm meter is very important.

An electrical component failure can result from a mechanical malfunction of control components such as improper opening and closing switch contacts. Limit trip arms sometimes knocked out of adjustment or broken off. Water in the tubes leading to a pressure switch, dirty contacts on relays and contactors. Component mounting bolts can come loose or break. The possibilities of mechanical failure are unlimited, therefore be sure to check for mechanical failure which would affect the operation of the electrical circuit/systems being tested. For another example if a limit switch fails to close due to a mechanical failure power will not go the the load device in the circuit.

It is always a good idea to check the fuel supply if natural gas is the meter turned on, oil is there oil in the tank, LP is the tank empty.

Watch out for switches that are on stairways, or hidden out of the way, electrical sub panels that sometimes the homeowners do not even know are there.

Start to think electrically - circuits consist of

Source or Sources of power

Loads - devices needing power to operate

Switches - to control flow of power to the loads from the source.

Isolate circuits by loads and work back to the source.

In one of our future posts we will give a step by step walk through for a circuit.

Unknown

What is the first thing to check

on electrical checks on a boiler or furnace?

Ben_3

checks

I first check my line voltage to the system, many times an old fuse has been the culprit of a no heat that is stashed away in an old disconnect that evryone had forgotten. I think it is also important to stress using all of your senses, i.e. sound, sight, smell, etc. For instance as one develops skill there are some checks you can make before pulling out your meter, however you have to use and understand your meter to be an effective troubleshooter. You may walk up to a furnace and the blower is running, it's safe to assume the line power is not the problem. All in all a through knowledge of electricity is vital as well an understanding of basic sequential operations.

Dale

On newer furnaces

I tell our techs to first look to see if there are any diagnostic lights blinking and see what the code is, if not remove the front panel and pull a wire off the high limit, the blower should start. Now we at least know we have 120 and 24 volts available. Usually the inducer is running which says we locked out, then recyle the power and watch the ignition try, depending on how far it gets we know where next to look. Often the vent is removed at the furnace to see if it's blocked. I think starting at the most common problems is the best strategy. We envy the dealers who only service one brand, so much easier to get quick as most problems repeat.

jim sokolovic

Don't skip the time it takes...

to get the actual voltages at the jobsite with your meter!
You can't assume that by seeing / hearing one component run, then there is the correct voltage / polarity / grounding necessary for other components to run properly. For example, a combustion blower can seemingly run fine at 90 volts, and doesn't care about polarity or grounding - while many ignition controls will not sense flame or even allow an ignition sequence if there is a problem with these parameters. Read hot to neutral, hot to ground, and neutral to ground, too! Feedback through the neutral can cause total havoc and is usually not diagnosed by the initial troubleshooter. Hope this input helps this lesson.

Unknown

Jim, Dale and Ben all good

points.

I suggest to techs that on electrical checks to go to the secondary of the transformer and check for POWER & POLARITY.
I call them the two "P's". This is accomplished by going from the "R" terminal on the transformer to ground (gas valve makes a a good ground for meter)you should read 24 volts. Then go from "C" terminal to ground you should read "Zero". If it is reversed the polarity on the primary side of the transformer is wrong.

I will follow up a little later with the next check.

jim sokolovic

Polarity sensitivity

Timmie (and friends), What components within the 24 volt circuit are sensitive to polarity? Of course, there are so many systems - but if I reverse the 24 volt wires on the transformer feeding an intermittent ignition control, it still seems to work properly. I have found that if I reverse the 120 volt wires on an integrated ignition control that has a flame rectification system, it will not register a flame current reading to prove the flame (and some controls won't even allow a sequence of operation to be initiated). Thanks for taking the time to discuss these subjects in detail!

Dale

Grounding the common 24

Almost all new furnaces and all new contols take the common side of the 24 volt transformer and tie it directly to ground. If you look at a schematic closely you can see where. This is done so there is a reference point for all circuits especially those that use flame rectification. If the common side is not grounded when it should be the control box sometimes fails in a short time ( guess how I know this ) . There is a relationship between the input and 24 volt output of a transformer. If you take a volt meter reading between the line 1 hot input or black wire and the R terminal on the secondary you should get 96 not 144 volts. If the meter gives 144 volts reverse the low voltage leads and ground the R instead of the C. You can do this test on the bench but need to make sure the primary neutral and secondary common are connected together. If that sounds strange remember that on a normal furnace the neutral is grounded in the panel and the common C of the secondary is grounded on the furnace. The reverse polarity lockout after ignition you spoke of comes about because the designers only use one side of the glow bar circuit to check for DC microamps and pick that side assuming correct polarity in reference to ground.

jim sokolovic

So the importance of polarity...

in the 24 volt circuit sometimes only has to do more with preventing components from failing after a short time, rather than getting the sytem to operate initially? This seems important for the field person to understand, to prevent frequent call backs. I work mostly in the experimental lab, where a short test would not reveal these problems. Of course, our products wouldn't be factory wired any other way but the proper known configuration!

Dale

Years ago

Over 20 now and I was in a night class listening to a guy, sadly now one of the dead men, who worked for Honeywell for many years before becomming a branch manager for a local wholesaler, he was talking about putting transformers in parallel and mentioned that you always test the last secondary connection because the transformer manufacturers sometimes get the R and C mixed on the assembly line. Of course it didn't matter much in the standing pilot days where the C wasn't grounded, now it does so understanding phasing and testing to determine polarity is worth learning.

Unknown

Good answers from

everyone.

Here is another one, I have 24 volts up to the gas valve. I find this by connecting one meter lead to "C" terminal on the transformer and the other to the switch side of the gas valve. The valve will not open - there is gas to the valve. What are the possibilities?

jim sokolovic

What kind of ignition system?

I notice most of the posts at this site seem to be in regard to standing pilot or intermittent ignition, where a pilot flame is established before the main gas opens. A direct ignition system does not have this. On a negative regulator valve, where usually the pressure of the combustion blower influences how much the valve opens, the valve may be opening, but you think that it is not, because the "reference" tubing is blocked or disconnected - giving a tiny gas flow that is not measureable or enough to light the burner.

Unknown

Overpressure

If the inlet gas pressure creeps up when there is no draw on the gas supply, and it gets high enough, the gas valve won't open.

Looks like a bad gas valve, but a new valve will do the same thing. Check your inlet gas pressure through several cycles to see if the pressure creeps up during long off cycles.

Noel

Dale

Besides the pressure too high

The wire from the C terminal to the gas valve C may be open or on a redundant valve the coils on the gas valve may be wired in series, TR/TH not being common, pilot lights but no main burner.

Unknown

Noel, Dale & Jim - Hey you

plumbing and heating guys do you agree with what these guys posted as answers?????

How about some of the field technicians joining in. If you are not I hope you are following this post - a lot of good info these guys are giving you.

Very good guys, just a few comments:

1. Over pressure is rare but can happen. I have experienced it especially when there are no pilot operated appliances to bleed of the excess pressure. It is very likely to happen on propane as we are operating at pressures closer to maximum allowed pressure on gas valves (1/2 pound - 14"W.C.). Important always check gas pressures before you condemn a valve. Power to valve will not open could be excess preesure.

2. Could be a bad gas valve - definetly, power to the valve will not open could be a broken coil in the valve.

3. OR as was posted "C" wire is broken no ground connection. GOOD TROUBLESHOOTING TECHNIQUE - if you have 24 volts on gas valve and it will not open, move meter lead to "C" terminal side of valve- you should read "0" (zero) volts if you read 24 volts the ground is broken. Fact any load device even motors if you read voltage on both sides of the load you have a broken ground.

4. On negative pressure systems with the combustion blower affecting valve opening - use a Dwyer Slant Gauge to check pressure differential - it must agree with the parameters as set down by manufacturers instructions. Or on equipment like the Munchkin you can adjust by checking your Carbon Monoxide reading and adjusting the throttling screw to get it into acceptable range.

Glenn Harrison

My first bet would be

a broken or open limit switch in the common ciruit to the gas valve. Some older furnaces were wired with the common thru the main limit, so you would have 24v between hot at the valve and common at the transformer, but zero between hot and common at the valve. You also could have the good old defective gas valve with a burned out solenoid coil, or a stuck diaphram. Could be a low gas pressure situation where there is enough pressure with the valve closed, but once the valve tries to open the pressure drops of due to a bad house regulator, (although I'll admit this is rare).

Unknown

More on Gas Valve

It could also be an old external escapement diaphragm valve with a bleed tubing going up to the pilot. You have 24 volts to the valve and it will not open, before condeming the valve disconnect the small 1/8" bleed tubing attached to the valve if the burner comes on you have a plugged bleed.

Unknown

I've often wondered when,,

we will meet.

I know it will happen. We have too much in common. I've read so many of your posts. I'm here in New England now. Time for me to make the time.

Pipedream

Unknown

Gary Wallace

I assume your post was to me. I would love to meet you some time. Just give me a call 401-437-0557, I am somewhat busy but I am sure I can make time.