Carrier gas furnace main gas valve doesn't get 24v to open up

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Old 12-05-10, 03:27 PM
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Carrier gas furnace main gas valve doesn't get 24v to open up

Don't know the year exactly guessing mid 80's has a black box with t1 t2 spark ignitor sends spark to pilot and it lights after that the 3 wire switch is suppose to send 24v to the main gas valve but does not replaced pilot with brand new one if I jump 24v to the red wire on the main gas valve it fire the main burners could this be possibly that the spark igniter is gone bad there is only two wires coming out of this box and one is common to ground and the other is blue going to the gas valve and then jumps two the pilot I am only getting like 9v out of this wire when the pilot is lite is this where the 24v is suppose to come from is there somthing wrong with the black box and it is not getting 24v out from there. also have my pilot mounted horizontally does it need to be mounted differently so the metal that acuates the switch is more affected. gone as far as my technical skills will carry me appriciate any help thanks
 
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Old 12-05-10, 04:26 PM
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A wiring diagram for a furnace like your is at:

http://www.xpedio.carrier.com/idc/gr...t/58ss-1si.pdf


Sorry, but I find your explanation too confusing to follow.

You need to describe the sequence of events, in order, that is happening when you turn up the thermostat.
 
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Old 12-05-10, 06:46 PM
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Is the pilot flame long and yellow? The reason i asked, when the pilot is removed and replace, at times the orifice may fall out and you don't notice. This has a dramatic affect on the pilot.
 
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Old 12-05-10, 08:09 PM
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mbk3 ---

he mentioned he'd replaced the pilot switch, so presumably a dirty burner or orifice isn't the problem.
 
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Old 12-05-10, 08:16 PM
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Sorry about the jumbled thread I could write about ten pages of things that I have done to this thing tried to keep it short and simple. In response to the pilot light reply it seems to be normal solid blue 3-4 inches and lights really quick 2-3 sec. The series of events when I turn on the thermostat I hear the click and from inside the house I can hear it click in the unit itself, then on the roof the pilot light starts to arc from the electrode and the flame lights up in a matter of 2-3 sec. and the spark continues to arc for maybe 4-6 times more and then stops (assuming that it has now regestured a proven pilot is my guess) after this it is suppose to send 24volts to the main gas valve which comes from a three wire switch located of the bottom of the pilot light the 24 volts is not being delived out of this switch. Is the wire coming from the spark ignitor routed to the three wire switch suppose to have 24volts because I am only reading 13 volts this leads me to think that something is wrong with my spark ignitor. sorry for the confusion hope this adds a little light to my problem
 
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Old 12-05-10, 11:42 PM
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When the pilot switch first turns on you should have 24 VAC at both terminal 5 on the gas valve and terminal T1 on the spark module.

The pilot switch typically takes about a minute to change states and the voltage on T1 and terminal 5 should go to zero.

At the same time, the 24 VAC should be switched on to terminal 1 on the gas valve, which should turn on the main burner gas.

Check to be sure you have 24 VAC at the W terminal on the circuit board when the thermostat is turned up..

If you have 24 VAC at W and 13 VAC at the spark module, you have a poor electrical connection someplace in between. You should check the voltage at the draft safeguard switch 7H2 and the common wire of the three wire pilot, listed as wire #1 on the circuit diagram on page 4 of the manual I supplied.

The draft safeguard switch is a likely source of the problem I would guess. The draft dafeguard switch has a manual reset and you may just need to push the reset button. If so, the switch tried to open but didn't open reliably and completely, allowing the 13 VAC to pass.

You need to identify where the voltage drops to 13 volts.

Why did you change out the pilot switch? I suspect the pilot switch wasn't the problem.

With a poor electrical connection the 13 VAC is apparently enough to get the spark module to operate, but not enough to power the main burner solenoid.

If my theory is correct, if you disconnect terminal 1 on the gas valve, you will see the voltage go to that 13 volts when the pilot switch heats up. Connect that wire again and the voltage should go to zero when the load of the gas valve is connected.


Anyway, those are some things to check out. You need to zero in on the cause of that voltage drop to 13 VAC.
 
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Old 12-06-10, 08:36 PM
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Found the problem

The pilot light needed to be moved so the metal tab that accuates the 3 wire switch would collect a little more heat. the guys that I paid 200-300 dollars to come out and fix it last winter on thier first attempt they didn't mount the pilot at all just left it hanging freely and when it light the pilot it was not close enough to the main burners and filled the chamber full of gas and blew the top off of my heater. Needless to say I got a little upset and threaten a few lives. second time they brought some piece of metal from god knows where and just mounted it where ever they could find a screw well by this time winter was over for us and haven't used the heater until know. But any ways figured it out and without your guys help I would still be beating my head against the wall. thanks seattle pioneer and mbk3 I speak as myself and I am sure on the behalf of many others your imputs are greatly appriciated. (by the way bought the pilot because I didn't take apart the 3 wire switch first and listened to my brother talk about high tech thermal somthing or other BS and found out later the switch is pretty much self explainatory).
 
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Old 12-14-10, 06:59 PM
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furnace is now running and needs a little correction on last answer

I found by trial and error that when dealing with this peticular pilot ignitor it has a deflector sheild that needs to split the flame in half that way the heat is deflected toward the piece of metal that acuates the 3 wire switch and also deflected upward so when the main gas valve is open a flame is present. (ss#LH80005 NG PILOT BURNER ASSEMBLY 733-40 3 WIRE) soory guys I dont know the year of the furnace all I know is that it's a carrier.
 
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Old 12-14-10, 08:01 PM
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Yes, you are correct. Part of the pilot flame needs to extend out to light the main burners and another part needs to heat the bi metal switch.


Sorry I was fixating on exotic problems earlier in the thread. Usually carrier pilots that light but don't light the main burner are dirty a nd need cleaning to provide enough heat to switch on the main burner.

But since you had replaced the pilot switch, that was unlikely to be a problem.

Usually even an un mounted pilot switch is going to put enough heat on the bimetal to operate the main gas valve, and I'm surprised you are still having problems.

You might want to post some pictures if you can. Apparently the original bracket that mounted the pilot to the burners was missing and a serviceman ginned up a replacement. That ought to be fine if it's properly positioned.
 
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Old 12-16-10, 04:59 PM
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I'll see what I can do about posting some pictures so others can see the situation. Again I would like to express my gatitude to you for your help. I just wanted to post a reply on how it got fixed. So many people get on these sites and ask a ton of questions and once they figure it out, they just disappear. I find this to be a waste of time to those who take time to help others. Thanks again guys
 
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