No power to my hot surface ignitor. Why?

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  #1  
Old 10-27-16, 06:08 AM
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Unhappy No power to my hot surface ignitor. Why?

I have Carrier Weathermaker 9200.
Had a bad HSI and a vacuum line from the Fan Inducer to the Pressure Switch was not connected. Fixed that and now there doesn't seem to be power to the HSI. I tested the power going to the HSI from the female connectors going to the HSI with the Multi Meter . I swear I saw a 120 reading earlier, however, I get a zero reading now. The pressure switch moves as if closing though I don't know if it is making good contact inside. The flame sensor is working and once I light the furnace it runs fine until it heats the house to temp and then shuts down. Vents and intakes seem clear. So what are the possible reasons that I am not getting power to the HSI and how do I test to find the possible problems?

Could junk have been pulled into pressure switch?

Can I bypass pressure switch just long enough to see if that is the problem?

I don’t have a vacuum meter for testing the pressure switch.
 

Last edited by saltydog463; 10-27-16 at 07:19 AM. Reason: some wrong info
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  #2  
Old 10-27-16, 06:27 AM
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For the purpose of troubleshooting the system you can connect the pressure switch wires together and see if that lights your HSI. DO NOT leave it jumpered and risk flooding your home with carbon monoxide.

I had similar symptoms on my water heater and narrowed the problem to a bad relay. I would measure 120V on the HSI terminals when disconnected, but 0 when hooked up. The relay was too pitted to pass the HSI current. I sourced a new relay for about $8 vs replacing the $150 control.
 
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Old 10-27-16, 11:20 AM
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When the thermostat calls for heat, it switches on the inducer motor. When the inducer motor comes up to speed, the pressure switch closes. When the pressure switch closes, the circuit board turns on the power to the hot surface ignitor.

You have verified that there is no 120 VAC to the HSI. The next step is to check to see if the pressure switch is closing. If it is closing, you will find 24 VAC on both sides of the pressure switch (measured from chassis ground)

That is, connect one side of the multimeter to the furnace chassis and use the other probe to check the voltage at the pressure switch terminals. If you have 24 VAC at only one terminal with the inducer motor running, the pressure switch isn't closing.
 
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Old 11-14-16, 06:12 AM
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Thanks. Please read my next post. Opps made a mistake. New post coming
 
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Old 11-14-16, 06:16 AM
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Thanks for the feedback folks. Below is all the info on the troubleshooting I have done.
Furnace works off and on. Sometimes power goes to the HSI and the furnace turns on and works fine ( about one in 15 tries. Other times the HSI gets no power and I get a #34 code. It seems that when the HSI doesn't work everything else is working fine. I've tested the pressure switch and the point where the pressure switch wiring plugs into the control board about a dozen times and the connections always test 25.4 -25.7 VAC. I've tested the HSI connection at the 9 pin connector at PL1 on the Control Board with no VAC readings most of the time. When I get a 120 VAC at the HSI the furnace starts fine. The HSI and the flame sensor are good.




When I start the furnace and it doesn't work the following happens.

1, I hear a click at the 9 pin connector and the inducer comes on. A VAC reading of .0 most of the time sometimes .1-2.5 at the HSI connection at the control board

2. At the 9 pin connector on the control board I hear and feel a small click 15 seconds after the inducer comes on. I get a VAC reading of .5- 8.9 most often around a 2.5VAC reading.

3. 15 seconds later I hear and feel a loud/bigger click at the 9 pin connector. Have always gotten a .0 VAC reading except one time I got an 8.9 and 120VAC a couple of times. When I get the VAC of 120 the furnace starts fine.

4. If the furnace does not start , about 4 seconds later there is another small click at the 9 pin connector and the furnace gives a #34 error code.




Is the clicking at the 9 pin connector a switch/relay on the control board that works on occasion? If so can that relay be repaired? Does this mean a bad relay on the control board and I need to replace the control board?
 
  #6  
Old 11-14-16, 06:31 AM
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If your getting a voltage reading across your pressure switch then that's a problem. The switch has opened.
 
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Old 11-14-16, 07:13 AM
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My test results for the pressure switch is for when the Inducer is running and before I get the code 34. The results are for each of the two connectors individually. One lead from my meter on a ps connector and one lead grounded as per a response from member SeatlePioneer below. roughneck77 I'm confused. What do you mean when you say "voltage reading across your pressure switch "? Thanks
 
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Old 11-14-16, 07:36 AM
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1, I hear a click at the 9 pin connector and the inducer comes on. A VAC reading of .0 most of the time sometimes .1-2.5 at the HSI connection at the control board
At this time.....when the inducer starts the pressure switch closes and HSI is not active

2. At the 9 pin connector on the control board I hear and feel a small click 15 seconds after the inducer comes on. I get a VAC reading of .5- 8.9 most often around a 2.5VAC reading.
At this time... the HSI gets 120v power. If the HSI comes on... the pressure switch is closed.

3. 15 seconds later I hear and feel a loud/bigger click at the 9 pin connector. Have always gotten a .0 VAC reading except one time I got an 8.9 and 120VAC a couple of times. When I get the VAC of 120 the furnace starts fine.
This is the gas valve relay and gas valve opening.

4. If the furnace does not start , about 4 seconds later there is another small click at the 9 pin connector and the furnace gives a #34 error code.
This is the gas relay shutting off due to lack of flame sense.

--------------------------------------------------------------------
There are two ways to measure the switches. One is from the switched side to ground or the leads across the switch.

I prefer the meter leads across the switch because not all furnaces use a grounded 24vac system. With the two leads connected to the two switch wires...... when the switch closes the meter should read 0v. If you see full voltage.... the switch is open. If you see partial voltage... the switch is defective.

At this point is looks like a defective control board.
 
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Old 11-17-16, 04:10 AM
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Just want to say thanks for all of the help. I ordered a control board and should get it this Tuesday. I'll let you know how it works out.
 
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Old 11-17-16, 06:25 AM
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Once your furnace is working again don't throw away the old control board. If you're at all handy with a soldering iron replace the HSI relay on the board & put it aside for a spare. The high current these ignitors require is brutal on the el-cheapo relays that are used.
 
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Old 11-17-16, 11:49 AM
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<<Once your furnace is working again don't throw away the old control board. If you're at all handy with a soldering iron replace the HSI relay on the board & put it aside for a spare. The high current these ignitors require is brutal on the el-cheapo relays that are used. >>


I disagree with that advice.

Furnace circuit boards are designed to be replaced, not repaired.

Replace the circuit board and ALL the different functions the circuit board performs are renewed. That's a definite advantage.

The current for an ignitor isn't much ---perhaps an amp at a guess.

Just not worth screwing around with a part that has a wide variety of safety related functions in your furnace.

If you succeed in diagnosing and repairing your furnace, you have saved a bundle by doing so. Be content with that is my recommendation as a furnace repairman.

I would NEVER make that kind of repair on a part and use it on a customer's furnace. Neither should you, in my opinion.
 
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Old 11-18-16, 06:48 AM
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And I'm not a board swapper. I would never throw away an expensive control board rather than replace a pitted $5 relay.
As a homeowner I have that luxury as I'm not being paid for my time in diagnosing to the component level.
Different strokes...
 
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Old 11-18-16, 08:30 AM
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It's not about money, it's about safety.
And I would never do anything to a customers furnace that I wouldn't do to my own. And I'd never try and repair my own control board.
 
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Old 11-20-16, 02:25 PM
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I installed my new/used control board I got for $40 on eBay and the HSI is working fine. Furnace starts and works fine. Thanks again.
 
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Old 11-20-16, 02:29 PM
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That's some good news.
 
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Old 11-20-16, 02:57 PM
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Yes it is. I could not have done this with confidence if it had not been for you and the other members. Hopefully this info will help some others. I do have a new intermittent issue that started while I was waiting for the new board. I confirmed it is still happening after installing the new board so it is likely not related to the HSI problem or the control board. I will post this new adventure later tonight or Monday. I need a rest. Have a Happy Turkey Day everyone.
 
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