furnace ignition module issues...

Timco

Scenario...Robert Shaw HSI ignition module. Replaced last week. Confirmed high voltage constant. Confirm low voltage loop is good, 26 volts every time t-stat calls for heat. Good inducer. Problem: Every 2nd to 3rd fire, ignition module stays off.(no LED) Check voltage high & low while failed, all good. With power on, pull vacuume line from inducer, suck manually. sometimes lights LED on igniter, sometimes not. After relay pulls in (Amana air Command...early 80's) I pull the harness (3-wires) from vac press switch, and jump terminals 1&3...sometimes LED comes on, sometimes not.(on ignition module) This is the d@#^&*est problem I have ever seen, module has been swapped out for a new one already...same problem. Intermittent failure. Maybe transformer amps?

Thanks,

Tim

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Empire_2

Sounds like the module to me

Just because it has been replaced, that don't mean it's any good. I have foun poor performing ignition modules in the past. If you have 24 VAC to the module and nothing happens. Scrap it!!! Consider a different module that is compatable. Keep your meter on the module while you are performing your tests and note what happens. Just because you are sucking on the pressure switch, are you sure 24vac in going to the module?

Timco

I kept the meter on the entire time, and always got 26 VAC. I scraped the first one, only to have the same problem. I tried jumping out the loop past the vac proving switch manually to rule out the switch...Two bad Robert Shaw 780-910s right out of the box??? Every time the relay clicks...26 VAC. every time. but some times, no LED at all...randomly...

Tim

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Larry Savino

What did you have as the original call,that made you think it was the board,

I had one I had to out on as a senior service tec for support (third time we were out on this call) it was an intermittent no heat and 2 boards were installed already.(its not to often you get 2 defective parts No less one defective part out of a box) Anyways as the unit was running the draft switch would drop out for a mili second then come back one,it di that about 3 times over the course of 20 minutes, Just for a mili second. We pulled out the draft inducer and found paint chips from the body of the inducer being pushed around inside the inducers body, just haphazardly landing on the port for the pressure switch opening it up every time it landed on the port. Vacuumed out the inducer,wire brushed the rest of the paint chips off the edge and it was back up and running.

We have a rule that if we are going to the same place 3 times in a season for a no heat or no cooling we send out another tec to help diagnose the problem and at that point we are doing an entire diagnostics starting at the thermostat wire connections and ending inside the panel box at the line voltage connections,

Good luck

My thought are I have replaced some worn out defective parts in my day but I cant think of any time I installed a part and it was defective out of the box. I can think of a couple of time I thought it was defective only to find the real problem after some searching.

Larry Savino

Last thing how is the ground?

Empire_2

Larry's on to something

Check that ground and the polarity on the 115vac to the furnace itself.

Timco

Ground is bonded well, and I checked voltage, but I did not check polarity. Do you suspect polarity would give intermittant fails? I suspected the switch as well, and that's why I jumped the terminals on the harness at the switch manually and got the same problem. This board was replaced because igniters were burning up once a season, due to the old moduld calling for 45 second warmup. This controler is set for 17 seconds now, and works great. In reading every word of the instructions, it does say that on a W/R replacement, you do not use the L2 or the hsi neut terminals on the module. I guess the module needs no neutral itself, and the hsi gets it's neut direct from the terminals in the JB. I'll try that today...

Tim

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Timco

Turns out the igniter module I was sold is not compatible with some WR replacement situations...specificlly older ones. Now they tell me....nothing I did. Could not tell me why...just is. Thanks for the thoughts. same volts, same terminals...whatever.

Tim

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