Furnace runs but blows cold

80% of the time, it's the sail switch

Propane full?

Do you have a propane leak detector that is past its expiration date?

Bionic Man wrote:
Propane full?

Do you have a propane leak detector that is past its expiration date?

All the other appliances work...stove, fridge, hot water heater. I don't think it's a propane issue as it just stopped igniting. I don't hear the igniter either.

RobWNY wrote:
80% of the time, it's the sail switch

I was afraid of that. Are you familiar with this unit and what is involved in replacing it?

Sail switches are effected by low voltage to motor not allowing in to come up to full speed. Many times sail switches contacts are not closing due to a very small piece of debris. Can quit often be blown out by compressed air.

The first thing I typically do for an RV furnace or water heater failure to ignite is disconnect and reconnect the wiring and ignition/sensor connectors a few times at the ignitor board to see if the problem is as simple as some contact corrosion. The ignitor/sensor connection in particular can be a problem since the sensor mode is working with millivolts. If that solves the problem, then I suggest using an appropriate contact cleaner at the first opportunity. I've worked on at least 100+ RV furnace problems over the years, and only replaced a couple of sail switches. The rest with ignition problems have generally been failed igniter boards, mis-adjusted or cracked igniters, failed gas valves, etc. Reseating the connectors alone has worked a surprising number of times.

Maybe Doug Rainer will stop in and lend his professional expertise to the problem...

Low battery is a common reason for furnaces not firing up - when a battery is low it won't run the furnace fan at high enough speed to open the sail switch. If battery is Ok then check the sail switch.

Thanks for all the info. Low battery isn't the issue as they were fully charged. I'll see if I can get compressed air to the sail switch. I did try unplugging and re plugging the contacts on the board terminals. I'll try some contact cleaner too.

Can of air with the tube works pretty good!

The sequence
T-state says "I'm chilly, Warm me please"
Control board starts blower blowing
Sail switch closes when blower is "up to speed"
Solenoid valve opens (Propane flows in theory) and igniter sparks.
Next step is an A/B Most Atwood and Suburbans are B
A: Thermocouple (Flame sensor) sends about 0.480 volts to the control board this causes current to flow and board says "OH. Flame is on" and heat continues till T-stat says "Ah. Nice and toasty, you can stop now" or Over temp cutout cutouts.

B: many Furnaces have a single wire ignition/sense system. in this system the wire carries roughly 1000 VAC during sparking and then switches to Sense lookin for the 0.480 volt DC thermocouple out. IF the TC (Thermocouple) is carboned up it may not get hot enough to generate the needed voltage and current.

Or if the change from Spark to Sense flubs Pop goes the sensor chip
(My theory of what killed mine.. And when I inspected the replacement which came from Dinosaur boards it appears it was their theory as well)

There is a LED on the furnace control board that will flash in most cases if it fails.. Whta is the pattern.

Page two... Even if it is working normally so much air flows it won't feel all that warm