Hi guys,

I have an old 395BAW Carrier furnace that started acting up this fall.

I turn on the furnace and call for heat:

The ID fan starts.
The spark ignitor fires up the pilot.
The pilot stays lit for 10-20 seconds, heating up the flame sensing strip.
Then I hear a few clicks and the pilot goes out. The pilot will re-light and go out, etc.

After some internet investigating, I thought the problem was the flame sensing strip. SO I called around and got a replacement three-wire pilot. Put it in, and... same problem...

I took my multimeter out and started testing the connections on the main gas valve... wrote it down but forgot to bring it with me. I can add this later.

I tested the limit switch for continuity and it seems ok. It gives 24V when the furnace is turned on.

I am not great with electrical diagrams or properly testing out each switch, or properly testing if the main gas valve will open.

Any help is greatly appreciated...

The furnace is the one found in this thread (I am not the guy who was posting in there): http://www.doityourself.com/forum/ga...ot-burner.html

 

I'm going to add something as I've been reading a bit more. The gas main to our house was just upgraded. Street/lawn all tore up. I thought this couldn't be related to the issue, as I've got a pilot light and my hot water heater and gas stove are working fine.

But I just read that some gas valves won't open if the gas pressure isn't high enough. (I thought part of upgrading the gas main was to increase the gas pressure...?). Could this be the problem at all? Would I increase the gas pressure by raising the screw on the gas valve? Or is this off the track of the real issue, as I initially thought?

Thanks in advance.

 

This could be your problem. Was the furnace working properly before the upgrade? Have the gas company come out and test the pressure.

 

The gas company is refusing to test it, based on the fact that my stove and hot water heater are functioning.

The gas burners on my stove are not functioning differently than before (not blasting more gas or barely leaking any through), so after some more thought I think the culprit may be the gas valve. But I am wondering how to test this electrically.
There are 5 connections to the gas valve:

spark ignitor T1 (green)
lower board & 3-wire pilot (white)
upper board (brown) - I believe this is mainly the induced draft switch
spark ignitor T2 (blue)
something else, I think it's another upper board (blue)

last two blue are also connected to each other via another wire.

(I am going off memory and will update later)

The gas valve is a white rodgers EF32CB197A, and it looks exactly like
http://www.ebay.com/itm/like/111467716714?lpid=82

 

Hmm, I can't figure out how to edit my posts. So I'll have to make a new one.

Here is an updated list of connections to the gas valve

(5) spark ignitor T1 (green)
(1) lower board & 3-wire pilot flame sensor (white)
(4) inducer board and flow sensing switch (brown)
(2) spark ignitor T2 (blue)
(3) inducer board (blue)

I used a multimeter to measure the 24V AC voltage during each portion of the pilot cycle. I measured between the white wire and the others. Except for the white wire voltage, which I measured between the white wire and "SEC-1". As far as I can tell SEC-1 is the power input to the board after the transformer reduces it to 24V.

So here are my readings:

Voltage before pilot lights --- voltage during pilot lighting and warmup --- voltage when burner tries to fire (this voltage only lasts a half second then goes down to zero)

(5) spark ignitor T1 (green) 0 --- 26 --- 14>0
(1) lower board & 3-wire pilot flame sensor (white) 30 --- 27 --- 27>0
(4) inducer board and flow sensing switch (brown) 27 --- 27 --- 15>0
(2) spark ignitor T2 (blue) 0 --- 0 (24 when pilot lights) --- 0.5>0
(3) inducer board (blue) 0 --- 0 (24 when pilot lights) --- 0.5>0

As stated before I also measured the voltage on the limit switch is 26V so that does not seem to be the problem.

here is a link of the wiring diagram
https://drive.google.com/file/d/0B93...ew?usp=sharing

 

Yes your right about the SEC-1. The way you have to measure the volts is to use SEC-2. For example to test 7H1 switch put one lead SEC-2 and the other on red #5 on the connector. Run though a cycle. You should have 24V through out the cycle. If it goes to 0V then the switch has opened.

Check to make the spark generator is grouded properly.

 

From your description it sounds like he "hold" portion of the gas valve has failed. The sequence should be... Close thermostat..pilot valve opens and spark generator produces spark to light pilot.. Pilot light and after about 30 seconds it transfers position and closes circuit to the valve and it opens momentarily. Since it is cycling off when the transfer is complete indicates to me the Hold of the Pick and Hold is gone. The way I test is something you may not feel comfortable doing. Seperate the pilot at the molex plug and install a jumper wire in the yellow and green holes of the harness, with the tstat closed that will energize the pilot and spark generator, after the pilot lights remove jumper and install it in the white and yellow holes, that should energize the valve. Now if the pilot goes out repeat the process using 2 jumpers but leave the first one in place when you add the second. If the burners fire that indicates you need to replace the valve

 

Well it ended up being the gas valve. I talked to a local service technician who found me a suitable replacement. Put it in and voooom! flame on!

Edit: thanks mbk3 for the explanation on jumpering, I did that and confirmed the valve was unable to open.

 

Thank you for coming back with conclusion