York RTU ignition problem

[bubs5985]

I got a call today for a youk unit m#: D4CG036N09225 not heating. Went up to the unit and found that it was not sparking. Had 24v to ignition controller, combustion fan running, all limits/rollouts switches closed. When the relay in the ignition control clicked, you could hear barley hear the spark. Tried to clean up the burner, sanded the pilot tube near the sparker and tried to light it again, no luck. I figured that the ignition controller was bad and not providing the spark necessary to light the pilot. Picked up a new ignition control, spark igniter, and flame sensor and installed them. The unit fired up and ran for a few minutes then shut off the burner, combustion fan still running. Main fan running and roll out switch still closed. Tried to fire it again and got the same weak spark that i seemed to be getting before. Had to leave the site because the business was closing and need to return tomorrow. I'm thinking it could be a grounding issue, but i did clean the grounding terminals on the gas valve. I did swap the placement of the sparker and flame rod, and the spark seemed to be good, perhaps it it a spacing issue with the new sparker? Has anyone had this problem before on an older your unit?

[marylandtech]

I had this same problem checked grounding new control/ignitor flame sensor everything. Try jumping out the rollout switch. In my case it had a slight resistance through the rollout switch and I assume a voltage drop to the igntion control. The ro switch attaches directly to the ignition control on the ro terminal correct?

[oldtimer2]

I think M-Tech has your answer, the roll-out switch, jump it out and see what happens. Your flame rod has to the furthest from your pilot supply, put the flame sensor and the ignitor back the way you found them! Is the carry-over tube blocked? do you smell gas out of the combustion fan outlet when it's sparking?

[bubs5985]

I'm headed over there shortly, i'll let you guys know what i find. I could smell gas and i did replace the flame sensor and sparker to their proper locations, i'll keep my fingers crossed for the roll out.

[bubs5985]

Jumping out the roll out switch worked! Got a new switch and put it in, unit is running normally again, thanks for the help!

[blackrh]

Have same problem, but ignition control ok, ro switch ok. When heat called for by Tstat combustion blower truns on, igniton and burner fire, runs about 5 minutes, burner shuts down. Combustion blower still running. If I reset, cycle repeats and I can keep doing this. What else can I look at? Thanks

[hands]

Have same problem, but ignition control ok, ro switch ok. When heat called for by Tstat combustion blower truns on, igniton and burner fire, runs about 5 minutes, burner shuts down. Combustion blower still running. If I reset, cycle repeats and I can keep doing this. What else can I look at? Thanks

Check the hi-limit.

[blackrh]

Will check this but if it is going out on Hi Temp would I be able to restart instantly after reset. I would think the Hi Temp would not have time to cool down.

[timebuilder]

Check airflow. Good belt, properly tensioned, clean filters, clean coil.

Hi limit is probably doing what it is supposed to do.

[steveholt]

Verify your primary voltage and the transformer secondary voltage.

Ensure that the transformer is grounded and fused.

Check your transformer wiring (if it’s a multi tap transformer).

Most unit come prewired for 220/240 volts ac. If your building is 208 volt and your transformer is wired for 240 volts, you will have a reduced secondary voltage.

This will cause your unit to operate intermittenantly. Somewhere around 18 to 19 volts ac, you ignition control can lock out on anything.

Based on what you found, place your meter across the complete safety circuit. If you drop more than 1 volt ac, across the safety switches , find the defective switch.

Place your meter across the transformer secondary winding, no load.
Press min max on your meter.
Jump R W
What is the min voltage recorded
Less than 20 volts ac – check your transformer and change if required.

Good luck…

[timebuilder]

Verify your primary voltage and the transformer secondary voltage.

Ensure that the transformer is grounded and fused.

Check your transformer wiring (if it’s a multi tap transformer).

Most unit come prewired for 220/240 volts ac. If your building is 208 volt and your transformer is wired for 240 volts, you will have a reduced secondary voltage.

This will cause your unit to operate intermittenantly. Somewhere around 18 to 19 volts ac, you ignition control can lock out on anything.

Based on what you found, place your meter across the complete safety circuit. If you drop more than 1 volt ac, across the safety switches , find the defective switch.

Place your meter across the transformer secondary winding, no load.
Press min max on your meter.
Jump R W
What is the min voltage recorded
Less than 20 volts ac – check your transformer and change if required.

Good luck…

That's very thorough. You got your thinking tewk on.

However, this is not a new unit, and it is a very fair assumption that it was working previously. So, that is going to take a miswired transformer out of the mix, eh?

[blackrh]

Did not check hi-limit. Made another final check on rollout switch and decided to check metal shelf on the companion unit and it is running cool. The one I am working on is running hot so found that the rollout switch is indeed tripping due to the heat build up. Now it looks like I will have to see if there is any blockage in combustion chamber, cracks, what ever. The vent motor seems to be running at speed. The pilot flame seems ok and no rollout from burners.

[D'Laine]

Check that the fan is running, the filters are clean, the return air is returning and the supply air is going out.
Really sounds like a high limit problem due to lack of air flow.

D.

[The Doctor]

recently found an inducer wheel on a york that was installed backwards with a heat exchanger job (http://hvac-talk.com/vbb/showthread.php?t=479802). see picture on post #1

[ricmar889]

oops, wrong post...still new to this

[steveholt]

An incorrectly wired transformer may cause intermittent lock outs, which can lead you astray looking for defective ignition components, etc.

I’ve encountered units 2 and 3 years old operating this way (some units installed by our own company personnel). Depending on the grid supply, when the 208 volt drops the unit may lock out.

Like all service guys, I like a solid failure. Find the defective component and move on. Troubleshooting intermittent failures is always a challenge.

A nice example of an intermittent failure is a transformer winding break down. Your primary voltage is in the correct range and your secondary voltage is 24 volts AC (28 -22) with a light load. On a call for heat, relays start to pull in - the transformer secondary voltage drops below 18 volts and the ignition module locks out on flame failure.

If you miss the voltage drop you can look in the wrong direction. If you catch the drop, change the transformer knowing you changed the correct part.

By the way, I wish I had a nickel for every part I misdiagnosed…

[tipsrfine]

Did not check hi-limit. Made another final check on rollout switch and decided to check metal shelf on the companion unit and it is running cool. The one I am working on is running hot so found that the rollout switch is indeed tripping due to the heat build up. Now it looks like I will have to see if there is any blockage in combustion chamber, cracks, what ever. The vent motor seems to be running at speed. The pilot flame seems ok and no rollout from burners.

A guy I work with had a similar prolem. Everything checked fine. He crimped the end of the burner next to the roll-out-that small gap on either side of the burner that allows the flame to light the burner next to it? Well, the end next to the roll out was a little too wide allowing flame to heat that metal housing the roll-out was mounted on.

[timebuilder]

An incorrectly wired transformer may cause intermittent lock outs, which can lead you astray looking for defective ignition components, etc.

I’ve encountered units 2 and 3 years old operating this way (some units installed by our own company personnel). Depending on the grid supply, when the 208 volt drops the unit may lock out.

Like all service guys, I like a solid failure. Find the defective component and move on. Troubleshooting intermittent failures is always a challenge.

A nice example of an intermittent failure is a transformer winding break down. Your primary voltage is in the correct range and your secondary voltage is 24 volts AC (28 -22) with a light load. On a call for heat, relays start to pull in - the transformer secondary voltage drops below 18 volts and the ignition module locks out on flame failure.

If you miss the voltage drop you can look in the wrong direction. If you catch the drop, change the transformer knowing you changed the correct part.

By the way, I wish I had a nickel for every part I misdiagnosed…

I can certainly respect that this has been your experience. However, I have not seen it here.

It's a great note for me to stick in the back of my mind. With that said, I have seen several hundred Yorks of this type group and not found a weak or miswired transformer in the bunch. What I do see is marginal rollouts and limit switches (found one this past Saturday) failed JCI ignition modules, and clogged orifices on the crossover tube. Less frequently I find a poor ground in the flame sense circuit, and just once, a heat exchanger that had been replaced without the required fire caulk around the draft box.

[jayhawker]

The roll-out switch voltage is compared to the ignition control, if the voltage supplied to the control for ignition is different from the the voltage sensed by the roll-out switch the control will lock out. Only takes a very slight difference to lock the burner control out, replace the roll out switch to eliminate the voltage drop if this is happening.

[tipsrfine]

The roll-out switch voltage is compared to the ignition control, if the voltage supplied to the control for ignition is different from the the voltage sensed by the roll-out switch the control will lock out. Only takes a very slight difference to lock the burner control out, replace the roll out switch to eliminate the voltage drop if this is happening.

How much of a drop from the roll-out will it allow?By volts.

[timebuilder]

How much of a drop from the roll-out will it allow?By volts.


For most limit contacts in series with a coil in a 24 volt circuit , I look for no more than .3 volts drop. However, if your safeties are going to a module instead of a contactor coil, then you will have far less current available to produce a voltage drop, and you could miss the high resistance of the contacts that can produce the drop when a current is passed through them.

If you are unsure about the differences in these two approaches to circuit design, disconnect the leads from the safety switch and measure resistance. A new limit will have perhaps .1 ohms across its contacts, and maybe .2 for a limit that has been in service. I write them up for replacement when they get higher than that.

If you find a handful of ohms, like 5-15, its a goner. Most likely, it has been tripped too many times to remain useful.

[tipsrfine]

For most limit contacts in series with a coil in a 24 volt circuit , I look for no more than .3 volts drop. However, if your safeties are going to a module instead of a contactor coil, then you will have far less current available to produce a voltage drop, and you could miss the high resistance of the contacts that can produce the drop when a current is passed through them.

If you are unsure about the differences in these two approaches to circuit design, disconnect the leads from the safety switch and measure resistance. A new limit will have perhaps .1 ohms across its contacts, and maybe .2 for a limit that has been in service. I write them up for replacement when they get higher than that.

If you find a handful of ohms, like 5-15, its a goner. Most likely, it has been tripped too many times to remain useful.

Thank you.

[jayhawker]

How much of a drop from the roll-out will it allow?By volts.

The rollout switch feeds a seperate tap into the ignition control. I have been told if the supply voltage to the ignition control is more than the voltage into the tap that feeds the rollout tap you should replace the rollout switch to prevent random lock-outs. This is on the OEM control that was original to the unit.