62" Ambassador Furnace Problems

[schwrtzmnn]

I am having a problem with the furnace in my 62 ambassador. It ignites and burns until it is hot enough for the fan to kick on, but after abuot 3 - 4 minutes, the fan kicks off and it continues to burn until it's hot enough to turn the fan on again. It seems to me that it should be able to run continuosly until the thermostat turns it off. I am also wondering where the ducting runs that provides heat to the bathroom, because insulation occaisonally collects in the grate where the heated air blows out. Any info is appreciated.

[dufferin]

Welcom to the forum, the best place on earth when it's time to talk about airstream.
I'll try to help you but first just want to make sure about something, does the furnace start to provide heat before the fan start to run?
usually the fan start, and after few seconds the burner start, and if the fan doesn't start the furnace should not start at all. I assume it is to avoid the chamber to get too hot.
After that when the set up temp is reach the burner can shut down but the fan still goes on... and again the burner goes on... it always takes a while for the fan to shut down even when you cut off the thermostat.

[lewster]

Originally Posted by schwrtzmnn

I am having a problem with the furnace in my 62 ambassador. It ignites and burns until it is hot enough for the fan to kick on, but after abuot 3 - 4 minutes, the fan kicks off and it continues to burn until it's hot enough to turn the fan on again. It seems to me that it should be able to run continuosly until the thermostat turns it off. I am also wondering where the ducting runs that provides heat to the bathroom, because insulation occaisonally collects in the grate where the heated air blows out. Any info is appreciated.

Welcome!

If this sequence of operation (SOO) is indeed true, than you have some MAJOR problems with your furnace! The SOO seems backwards. Essentially, when the thermostat calls for heat, the blower fan will start to purge the combustion chamber and start the flow of air thru the ducting. It also closes the fan switch to allow current to flow to the gas valve so it opens to allow LP to the burner.

With the gas valve open, the igniter (or pilot) provides the flame/spark for the burner to ignite. The furnace heats and warms the trailer until the thermostat is satisfied. The burner is then extinguished and the blower continues to run until the TDR( time delay relay) cools or igniter board tells the fan to stop. The furnace is then ready to again be activated by the thermostat.

While this is a bit oversimplified, it has the major components and order. If the burner comes on WITHOUT the blower, there is a serious cross wiring going on. I would have it checked by a qualified professional soon!

[schwrtzmnn]

ok thanx for the info!

[schwrtzmnn]

It seems to me that the sequence is correct, like a home furnace, the heat starts to generate, then when there is sufficient heat availible, the fan turns on to distribute it around the trailer. I could be wrong, but I think the combustion chamber is not putting out the amount of heat that it should, possibly due to clogged LP ports, or debris in the chamber. Does this make sense to anyone?

[lewster]

Originally Posted by schwrtzmnn

It seems to me that the sequence is correct, like a home furnace, the heat starts to generate, then when there is sufficient heat availible, the fan turns on to distribute it around the trailer. I could be wrong, but I think the combustion chamber is not putting out the amount of heat that it should, possibly due to clogged LP ports, or debris in the chamber. Does this make sense to anyone?

RV furnaces ar not the same as domestic furnaces. The fan should be on first before any ignition and heat production occurs. One of the safety features of an RV furnace is an over temperature thermostat (limit switch) that will open the electrical circuit if the furnace gets too hot. One scenario for this is having the burner on with no air flowing across the plenum. This would cause the gas valve to close and the flame to extinguish. Unless this is NOT an RV type model, they justdon't operate that way.

You should have it checked!!!

[schwrtzmnn]

Thanx, I'll have to get it looked at.

[scottanlily]

On my 60 trdwnd ,the furnace lights ,and heats fine ,it needs to get hot
as well for the blower to come on ,it does not just come on right away.
Also ,the design as i can tell is that the blower IS for circulating the hot
air .It has a manual vent you move with a pull lever to close the air to the lower front ,and direct it back to the bath ,where it travels thru a tunnel
formed from aluminum (original to the trailer) and exits at the floor/wall in the
bath thru an opening in the wall (round 2" hole with mesh screen ).Now ,
the furnace has a 12volt blower behind the furnace ,and a thermocouple switch up the furnace housing for the heated air to warm it to start the blower motor fan assembly,there is a transformer (original) that converts 110 to 12v when on shore power is on (wall switch by the furnace ,shore or 12v.)
anyway ,this is how my furnace works .This is the original unit in my coach
and it looks like the style most of these early trailers used ,looks like a 60s
home wall furnace ,the kind that usually was in the hall way of many homes.
Im sure that the newer styles of today ,and even 20 years ago were different
in there design ,but not in my case ,and most likely schwrtzmnn 's furnace
works as mine does ,it sounds like it .Id venture to say that the thermoswitch
that turns on the blower is cooling off too quickly ,shuting the blower off
until it gets hot enough to turn the blower on .Mine isn't exactly working
perfectly either in this regard ,it will run the blower for a long time ,then sometimes it takes a long while for it to switch on .

Scott of scottanlily

[schwrtzmnn]

thanx Scott. Your furnace sounds very similar to mine. When I find The problem I'll be sure to let you know what was causing it.

[lewster]

It must be a vintage thing!

This is the first I've heard of an RV furnace that works like this, but then I haven't worked on any 60's vintage trailers yet. If it is indeed as you say and the blower needs the thermoswitch (could be a time delay relay or something similar) to reach operating temp before it turns the blower on, then this is the component that may need to be replaced.

As an experiment, when you light the furnace, try jumping across the terminals of this switch, if the blower comes on and STAYS on, then you know for sure that it's this component.

Hope this helps!