Propane heater troubleshooting?

[Ralph L. Fullenwider]

Hi: Here is a place to start.

I just got back from the Tulsa area. Here is the sequence of operation for
the furnace.
--------------------------------------

The thermostat controls the operating circuit to the furnace by reacting to
room temperature.
When room temperature is below the thermostat set point, the contact closes
to allow current to flow to the relay.

The circuit breaker limits amperage draw of the motor.

The time delay relay (TDR) allows current to pass to the motor by closing a
switch within the TDR.

The TDR is normally an open relay. When activated it closes, sending power
to the blower motor.

When deactivated it allows blower to run for a period of time to cool the
combustion chamber.
A heater coil within the relay actuates a bimetal disc which closes the
relay circuit. This takes approximately 20-30 seconds. Current flows to the
motor to operate the blower. One end of the motor shaft is for the
circulating air wheel and the other side is for the combustion air wheel.
As the circulating air wheel comes up to speed, it blows air against the
sail switch and closes the contacts (at approximately 75% of the rated air
flow), completing the circuit. The sail switch is a safety device (air
prover) that insures adequate air flow before ignition. The limit switch is
a safety device that protects the furnace from overheating. The con-tacts
in the limit switch open at a given temperature setting, shutting off power
to the direct spark ignition (D.S.I.) system that controls the gas valve.

As power is applied to the D.S.I. board, the system does the following:

1. A timing circuit in the D.S.I. board allows the blower to purge the
chamber (approximately 20 seconds).

2. The board supplies current to the gas valve and causes it to open. A
manual electrical switch is provided on some models and must be in the ON
position for current
to reach the valve.

3. As the valve opens, the board sends a high-voltage spark to the
electrode at the
burner. The board detects the presence of a flame. If the flame is not
sensed after
approximately seven seconds, the board will lock out after three tries for
ignition.
Some older models have single try boards.

4. If the system does not ignite and the thermostat remains closed, the
blower will
remain on until the thermostat is reset manually. When the thermostat
senses the desired room air temperature, the contacts open, removing power
for the time delay relay and the D.S.I. board, shutting off the gas valve
and shortly thereafter the blower motor. The blower runs until the heater
in the time delay relay cools and opens the circuit, shutting off current
to the motor.
----------------------------------

Bedroom unit: be sure the thermostat is switched off. Open the grill and
remove the front cover of the heater, this will allow you to get to the
igniter unit which is under the small round window. Remove the 2 screws
holding the igniter unit in the chamber and carefully pull it out. Clean
the probes of all soot then be sure there is a 1/8th inch gap between the
probes. With a flashlight, check inside the chamber for dauber nests, then
re insert the igniter unit and re install the screws. Now switch on the
thermostat and look for LP ignition in the round window about 20 seconds
after the blower motor comes on. You should also hear a "click" just before
ignition, this is the LP valve opening. If flame then button the front of
the heater up and your done.

Kitchen: Try following the sequence of operation listed above to start your
trouble shooting.

Good luck,

Safe travels,

Ralph and Charolette Fullenwider
Ralph's RV Solutions, Duncan, Oklahoma
http://home.swbell.net/rlf47/index.htm



At 02:19 AM 1/19/2006 +0000, you wrote:
>We have a 1977FC31 that we love. Just back from a trip from Tulsa area
>to Padre Island and back without a hiccup. We did have an issue with
>the heat though.
>
>Can anyone help?
>
>Our heater in the front area works great, the bedroom unit blows air
>when you turn on the thermostat,but no heat, the kitchen unit does not
>do anything. Where do you start troubleshooting? The tank has propane,
>the range works fine as does the front heat. The bedroom unit is under
>the bed and I am not sure where the kitchen unit is as there are
>several registers but nothing happens with any of them.
>
>
>