Atwood furnace problem..again

[Bigdog]

I have had to replace the motor and board on my front furnace twice and the board and burner tube on the rear once in the three years I have had this MH.
Now the front unit,replaced in 3/12 is only blowing cold air and doesn't even click to indicate it is working. The rear one is working fine and I'm getting gas to the stove and the water heater.I really hate to have to take it to the dealer,but may just have to.It seems as if everything that breaks is just out of the warranty period when it goes.

[enblethen]

No the motor starts first, then the power goes to the circuit board via the sail switch, limit switch.

[Old-Biscuit]

dougrainer wrote:

enblethen wrote:
Doug:
Not exactly right on the time delay relay. The secondary contacts that close after the pre determined time could be bad.

I AM right. ALL the Time delay does is delay the motor start and once that is done the Time delay is functioning. I have NEVER seen a time delay start a motor and then cause an ignition problem. Doug

Time delay relay is just a simple coil relay
Power on one side of contacts
Power to coil side of relay...coil heats up
Contacts make up on other side and power flows thru

Power removed from coil side
Contacts remain made up until coil cools off
Power no longer flows thru relay

All it does in rv furnace is start fan and stop fan

[Bigdog]

Blew the tube out with canned air and no go,checked all the connections.Pulled the ones I could reach and hit them with an emory board and they all looked good. Hit the switch and ran the thermostat up to 75 degrees and the blower came on,but no burner. Will be calling a mobile repair guy first thing in the AM.

[dougrainer]

enblethen wrote:
Doug:
Not exactly right on the time delay relay. The secondary contacts that close after the pre determined time could be bad.

I AM right. ALL the Time delay does is delay the motor start and once that is done the Time delay is functioning. I have NEVER seen a time delay start a motor and then cause an ignition problem. Doug

[enblethen]

Doug:
Not exactly right on the time delay relay. The secondary contacts that close after the pre determined time could be bad.

[Bigdog]

I think that I'll put on some warm clothes and head up to the MH and get the invoices for the work they did on the furnaces and see what was replaced.
Gotta put up some more Christmas lights anyway. I had to quit yesterday as the hole in my neck where they removed a golf ball sized growth from a salivary gland last thursday was starting to ache pretty bad.Kinda cool as they used super glue to hold the inscision closed and then put a clear spray covering and then an anti-biotic ointment over that. I can't see it as it's behind the jawline,but the DW took a pix and it really looks nasty.

[dougrainer]

Bigdog wrote:
All I hear is the blower motor. It starts up and just keeps running. No clicks,roar or anything.

Atwood----Either the Sail switch OR the hi limit switch will cause NO power to the Control board to start ignition. Your year model has a separate Time delay which is working since the motor runs. Your year model, UNLESS they replaced the control board with the original model will leave the fan ON if no flame. USUALLY, in the past 7 or 8 years, when the control module is replaced you install a new style with a fan cut off circuit to stop the blower when no flame. Doug

[enblethen]

Many Atwoods do not have the time delay on the circuit board.
It is a separate part mounted to the fan housing.

[Bigdog]

All I hear is the blower motor. It starts up and just keeps running. No clicks,roar or anything.

[wa8yxm]

I need to boiler plate this, In fact I think I will.

WHat happens when heat is called for:

Thermostat calls for heat
Control board starts blower
Sail switch is closed by the force of blowen air on the "Sail".
Control board opens propane valve and starts making sparks (DSI)
Options 1 of 2
Control board continues ignition for brief (3 seconds?) time then looks for flame report (0.480 volts from flame sensor probe) (Same lead as ignition)
Option 2
Control board continues ignition and looks for flame report on separate flame sense lead.

If flame is sensed it shuts off the sparker.

In both cases.

If flame is sensed, operation continues till T-stat shuts down

If no flame is sensed, It tries again, and if needed again. Then locks out and fires up the FAULT light. (if you have one).

If it continues. When it gets hot enough the T-Stat says "ENOUGH already" and the flame is cut off (propane flow) followed by a brief cool down and shutting down of the blower.

If at any time the furnace gets too hot, OR the air flow is reduced to the cut off for the sail switch. IMMED shut down of flame.

[spadoctor]

uhhhhh....he said its an attwood furnace.

[D_E_Bishop]

I agree with dougrainer, replacing that many parts is unusual. If it is something you can do, I'd pull that puppy out and check it out fully. Pull your board and have it checked at a RV shop. There are devices for doing that. If there isn't any board, pull and clean all the connections. Something weird is happening in your heater. Check Suburban's website for repair manuals. They may have them in PDF format. I'd PM Chris Bryant and ask him about trouble shooting and repair manuals in PDF.

On Edit:

For spadoctor, I'm so very sorry, I put down Suburban and not Atwood. Please change procedure to check Atwood on line and check with Bryant about Atwood heaters.

[dougrainer]

I think the FIRST thing is a check out by a QUALIFIED RV Tech. Replacing all those parts in such a short time span is not correct. The motors last for years and the circuit boards rarely fail. The "burner" tube is also a rare failure, unless it was corroded. Do you still have the 2001 RV? If so, I would lean towards replacing the complete furnace(13 years old). Internal corrosion is what would cause the Motors to fail that quick and if the motors corroded, then the interior casing and such may have corrosion. Doug

[enblethen]

Dirty sail switch
Bad time delay relay.
I would start by opening unit up and giving it a good blow job with some canned air. Look for the sail switch arm, extending into the blower housing. make sure you hit it good.