Question To you HVAC folks

On Sat, 10 Jan 2004 18:12:43 -0800, Gunner wrote (in message ):

My long distance guess: Bad gas solenoid. Second possibility, the contact in the controller that feeds the gas solenoid is burned.

Hope this helps.

Roger in Vegas Worlds Greatest Impulse Buyer

My best guess from my chair and with a little hands on experience with controlers that your problem is your flame sensor. If my memory serves me correctly you can take a 1.5 volt battery with a 15K ohm resistor in series and bypass the flame sensor . This will confirm the flame sensor function .

I have seen some of these problems in the past caused by open inspection plates that allows drafts to blow the flame askew and by debris on the flame holder that slighly deflect the flame.... all worth looking at.

good luck.

That's my guess too, I don't think the flame rod could cause that kind of problem (but I'm coming at it from the other side..). Check the

24VAC at the controller- make sure it's in the right range and fairly steady as the gas valve is energized.

Best regards, Spehro Pefhany

The blower unit worked OK, but did they actually hook it to a gas valve? Or, did they just hook a meter to the gas valve terminals? That might not be a good enough test. Assuming an AC gas solenoid, they probably use a triac (SSR) to drive the gas valve. These can have all manner of odd failure modes. You should hook a DVM to the solenoid leads, and see if the 24 V AC is going on and off. If so, it is the control. If a stady 24 V AC is going to the solenoid, then it is the solenoid valve that is bad. You can also connect the solenoid valve to 24 V AC and see if it holds steadily or clatters.

Jon

24vac is steady on input, but flakes out to the gas solenoid during the ignition sequence. I removed the coil from the solenoid from the circuit, thinking there was perhaps a short, ohmed it out, ok, refired the system and the 24vts still only fired for a second or so without the solenoid in the circuit. I would automaticly replace the controller, but the boss indicated it worked fine at the dealers so it should work fine yada yada yada... shrug.

Gunner

"Gun Control, the theory that a 110lb grandmother should fist fight a 250lb 19yr old criminal"

the controller is a sealed unit, containing what I believe are solid state switches. I was unable to feel even the slightest TICK when the ignition sequence would fire.

Gunner

"Gun Control, the theory that a 110lb grandmother should fist fight a 250lb 19yr old criminal"

Turn off the gas, turn of the power, wire the solenoid directly to the transformer, turn on the power. Does the solenoid hold in? If not it's a bad transformer or solenoid. If it does your flame sensor is bad. My bet is a bad winding in the solenoid or transformer that shorts or opens under its own induced field.

Loyd

Blink blink..ok....Ill try that. Ill also try that with the gas on at the appropriate time in the ignition cycle and see if the flame rod ever stablizes or has a rectification.

I hate working with electrically operated natural gas devices that use a 1" gas line. Ive lost my eyebrows more than once...

Gunner

"Gun Control, the theory that a 110lb grandmother should fist fight a 250lb 19yr old criminal"

On Sun, 11 Jan 2004 06:24:36 GMT, Gunner brought forth from the murky depths:

Silly wabbit. Try one of these next time, eh?

-- Vidi, Vici, Veni ---

Comprehensive Website Development

"Gunner" wrote in message news: snipped-for-privacy@4ax.com...

I should have said the flame sensor circuit/system. Now, I am assuming that you haven't changed out the controller, because if you have and you have an external purge timer you just need to read the installation instructions regarding that situation. I am also assuming that the controller hasn't gotten wet as that could cause problems. That said, maybe this will be clearer.

Turn off the gas. Turn off the power. Check the flame sensor wire to make sure it is not damaged and that it isn't touching anything to which it can ground out. If it appears ok then check the following. Mark the wires so you can reconnect them in the same manner as switching leads may cause the system to lock out. Disconnect the secondary of the transformer from everything. Disconnect the gas valve. Wire the transformer directly to the gas valve solenoid. Turn on the power. Does the gas valve open and stay open or does it chatter(open close open close open etc)? If it opens and stays open the transformer and valve are fine. If it chatters then one or the other is bad. Since you say the 24V is constant it is apparently the solenoid. If the transformer and gas valve solenoid are good then the problem lies in the flame detection system/circuit. Turn off the power. Rewire the transformer and gas valve as they were originally. Loosen and retighten the flame sensor mounting screw. See if that solves the problem(bad ground). If not, remove the flame sensor, disconnect it from the controller at the controller, attach meter to lead end disconnected from controller and base of sensor(ground), heat sensor with a propane torch to see if it produces the 0.8uA minimum through the lead. If it doesn't, disconnect the lead from the sensor and test the sensor again to see if it produces the 0.8uA minimum. If it does the lead is bad. If it doesn't the sensor is bad. If both check out as working properly and you are confident that the moving of the lead hasn't just happened to alleviate a ground in the lead, then the problem lies in the controller(unless you did alleviate a ground in the sensor lead). From your description of what's going on it sounds as if the problem lies in the solenoid circuit. It could be the solenoid or it could be the controller isn't holding in the solenoid circuit. Since it happens during the start-up I doubt it is the flame sensor. I guess is that it is the solenoid or the controller.

Loyd

In this case, is the flame sensor a thermocouple?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

These units use a rod sitting out in the open flame. They sense the rectifying action of a flame, which is very insensitive to soot contamination or other undesired side effects. Needless to say, a false positive flame detection would be a very serious matter. Flame out, gas valve stays open, ssssssssssssssssssssssssssss, mixing with air, seeping out, searching, until it finds *another* flame, anywhere.

Best regards, Spehro Pefhany

What's the gas pressure to the unit? I installed a new furnace a few years ago that wouldn't fire the main burner. Turned out the pressure was slightly higher than the valve could take. Old furnace worked fine for many years at the same pressure....Paul

Your question brings up other issues. I'd assumed it was a piece of equipment that was already in use. Is the equipment new? Had it been working and stopped? Had repairs been done to it recently and if so what? Your point about the gas pressure is a good one, especially if the equipment is new or the gas valve has been changed.

Loyd

No..the flame rod is a device that puts 100 or so volts on the flame rod, which is exposed to the flame, and uses flame rectification to convert this to dc and then to ground. It senses the ground path

Gunner

"Gun Control, the theory that a 110lb grandmother should fist fight a 250lb 19yr old criminal"

Thanks, I've learned something today. I've never seen those, all the flame decectors I've been aware of are either thermocouples or CdS photocells.

Also the SiC ignitor modules in our oven - which always seem to burn out at the *worst* time!

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

[about a Honeywell gas control...]

I have a "Seahorse" heater with a Honeywell VR8204M control that uses one of those. I could never measure any self-generated output from it, and was under the impression that it rectified power supplied by the controller rather than sourcing its own thermopile current. Is that what you are saying here?

Is there some way to test those with multimeter, maybe while they are connected to their controllers?

My problem turned out to be that the pilot assembly, with the sensor rod and hot flag, had been bent out of position during manufacturing. If the heater had been off long enough for the gas in the burner lines to dissipate, then when the main gas valve re-opened it created a gust of air that turned off the pilot sensor before the burnable mixture could get to the pilot and ignite. It seems those "rectifying" sensors are a _lot_ faster to turn off than a thermopile would be! Moving the pilot assembly to its proper position let the sensor stay on long enough to ignite the main burner.

Loren

Some of the big industrial ones use a special electronic gas tube that is sensitive only to ultraviolet light. They are sunlight-blind even without a filter but respond to the UV given off by a flame.

Same thing with the hot-surface ignitor in our furnace. I should pick up a spare.. thanks for reminding me.

Best regards, Spehro Pefhany

I ran into a simlar problem on our furnace. A friend suggested that I check the "flame sensor". In my unit it was a stainless steel rod that stuck into the flame. I removed it, it is on a little bracket, and cleaned it with denatured alcohol and when I reinstalled it the furnace worked fine. My friend said that after years of being stuck into a flame, the sensors get coated with a fine film of ash that insulates it. All I know is that a good cleaning solved my problems. Terry