Great site!

I have a Carrier Model # 394JAW048080

The blower does not come on and after the pilot is lit (electronically) the main gas does not come on.

I previously had a tech come out and diagnose the thermocouple for temp overlimit a few years ago and I replaced the unit for $15 in 5 minutes.

Since he said they go bad more often than other parts, I focused on that this time.


When I disconnected a lead from the thermocouple, the blower came on, but the pilot went out. I figured that this must be the culprit since both the heater and pilot light were affected. I am guessing that the thermocouple needs to present a resistance greater than 0 for the blower to operate but not open for the burner to operate.

Is this correct?

I measured the resistance on the thermocouple and it was .5 ohms. (I used the 1 ohm scale.)

What should it be?

Also I noticed an in-line (resistor?) at the connection to the thermocoupler. I measured the resistance to that and it was 0 ohms. That seems weird. What should that be? Does anyone know the PN or rating of that so if I have to replace it I can get one at Radio Shack? It looks like something tha may not be at radio shack. Any suggestions as to a source?

I thought thost units had a 3 wire pilot?

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Originally Posted by hvac1000

I thought thost units had a 3 wire pilot?

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Actually the part I was talking about is the High Limit switch. I just got a new one and the problem is still there.

The pilot lights, but the blower does not start.

If I disconnect the lead from the high limit switch, the blower starts and the pilot turns off.

What should I test next?

When I disconnected a lead from the thermocouple, the blower came on, but the pilot went out. I figured that this must be the culprit since both the heater and pilot light were affected. I am guessing that the thermocouple needs to present a resistance greater than 0 for the blower to operate but not open for the burner to operate

This is what you first said so post a picture of the part you are now talking about.

Quote:

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Originally Posted by hvac1000

When I disconnected a lead from the thermocouple, the blower came on, but the pilot went out. I figured that this must be the culprit since both the heater and pilot light were affected. I am guessing that the thermocouple needs to present a resistance greater than 0 for the blower to operate but not open for the burner to operate

This is what you first said so post a picture of the part you are now talking about.

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Originally, the part I was talking about was the high limit switch or gas limit furnace thermostat PN SHL 504 .

Now that I replaced it with a new one I am looking at other potential causes.

I read another post from you about the 3 wire safety pilot assy. And I proceeded to reseat the connections to that - one time I got the heater to start up fro a couple of minutes but I heard a relay clicking and it went on/off a few times and then off.

In the other post the poster had retightened the thermostat leads and it worked again. You said that is common with these three wire pilot assys.

How can I best test the three wire pilot assy?

Quote:

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Originally Posted by Tom in norcal

Originally, the part I was talking about was the high limit switch or gas limit furnace thermostat PN SHL 504 .

Now that I replaced it with a new one I am looking at other potential causes.

I read another post from you about the 3 wire safety pilot assy. and I proceded to reseat the connections to that - one time I got the heater to start up fro a couple of minutes but I heard a relay clicking and it went on/off a few times and then off.

In the other post the poster had retightened the thermostat leads and it worked again. You said that is common with these three wire pilot assys.

How can I best test the three wire pilot assy?

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Can't get any better than this. Bryant and carrier are kissing cousins so I supplied you with the wiring diagram for the three wire pilot and the rest of the wiring. NOW if this has a thermocouple that screws into the gas valve as you said in one of your other posts see drawing two.



http://i151.photobucket.com/albums/s...arrier58SS.jpg

http://i151.photobucket.com/albums/s...GSdiagram2.jpg

Did you pull out the pilot module and clean it?


http://img160.imageshack.us/img160/6484/50815447zu7.jpg

Last but not lrast IID pilot style. Now you have them all from that seriers so it has to be one of them.

http://i151.photobucket.com/albums/s...er58GP58GS.jpg

Thank you so much for your info. I called a service tech out and paid $45 for a diagnosis. They offerd to replace the control board for $350. I called a parts place got one for $50 and installed it in 15 minutes. The only problem is that it did not fix it.!

I will look at what you have sent Tuesday.

Sounds like the pilot switch is not changing over to the hot contacts. If this occurs, the main burners will not light and the blower on-delay timer will not be started. Try this: after pilot lights, disconnect pilot harness and jumper yellow - green (on furnace side of connector). If burners light followed by blower operation, replace the pilot assembly.

The 3 wire pilots were good service calls back in the day.

Quote:

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Originally Posted by KC13

Sounds like the pilot switch is not changing over to the hot contacts. If this occurs, the main burners will not light and the blower on-delay timer will not be started. Try this: after pilot lights, disconnect pilot harness and jumper yellow - green (on furnace side of connector). If burners light followed by blower operation, replace the pilot assembly.

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Thanks for the idea.

I did what you said but nothing happened. I have replaced the HL switch (measures as a closed circuit) and the control board.

A tech came out and diagnosed it to the control board but he was wrong. He said he checked that the signal voltage was coming from the pilot switch but not from the control board.

I wonder what terminal on the main valve should have voltage from the control board relay?

Hi all,

I had another tech come out since the first guy mis-diagnosed it. He swapped the pilot light assy and the high voltage transformer to no avail. It was the main gas control valve that solved the problem.

Thanks for your help!