heater blows cold air for about a minute then shuts off

[jhenretta]

I have a grey wolf 26dbh and the heater used to work great. on our last campout, it quit working. It turns on but just blows cold air for about a minute and then shuts off. There is plenty of propane and i have turned the stove burners on to make sure there isnt any air in the lines. Ive tried multiple times but cannot get the heater to fire on. Any advice would be appreciated.

[dustman_stx]

Originally Posted by jhenretta

I have a grey wolf 26dbh and the heater used to work great. on our last campout, it quit working. It turns on but just blows cold air for about a minute and then shuts off. There is plenty of propane and i have turned the stove burners on to make sure there isnt any air in the lines. Ive tried multiple times but cannot get the heater to fire on. Any advice would be appreciated.

Most likely the sail switch. If it doesn't sense the fan blowing it won't allow the heater to turn on the gas valve and ignite.

[Flybob]

there can be several issues.

You can have someone listen on the outside of the RV near the furnace vents and turn up the thermostat. You should hear the igniter clicking as it tries to light. No clicks means the control board is bad or the furnace is in safe mode. If the propane was turned off but the thermostat still on and the furnace tried to start it could have gone into safe mode. If this is the case, you can reset the controller by pulling the furnace fuse waiting a few seconds and reinserting it. Normal operation when thermostat calls for heat is turn on fan for a minute or two then attempts to light ( clicks). Once it lights the heat from the flame is sensed by a thermocouple and the furnace continues normal operation.

[Scrapper]

There is a Service manual that covers most Suburban furnaces in the Library section of this forum.


http://www.forestriverforums.com/for...?do=file&id=67

[Skip12]

That happened to me due to low battery even when connected to shore power. Low battery resulted in not enough fan power to trigger the sail switch, as Dustman described.

[jhenretta]

Originally Posted by Flybob

there can be several issues.

You can have someone listen on the outside of the RV near the furnace vents and turn up the thermostat. You should hear the igniter clicking as it tries to light. No clicks means the control board is bad or the furnace is in safe mode. If the propane was turned off but the thermostat still on and the furnace tried to start it could have gone into safe mode. If this is the case, you can reset the controller by pulling the furnace fuse waiting a few seconds and reinserting it. Normal operation when thermostat calls for heat is turn on fan for a minute or two then attempts to light ( clicks). Once it lights the heat from the flame is sensed by a thermocouple and the furnace continues normal operation.

we disconnect the battery when the trailer is not in use yet still had the same issue the last time we used it. would disconnecting the battery be the same as pulling the fuse to reset the safe mode?

[Jerrell]

Check for cobwebs and insect nest in vent tubes.

[SimchaSabre]

I also had a bad over temp sensor that failed open.

[UT_Grandpa]

Disconnecting the battery either by the disconnect switch or pulling the negative lead is the same as pulling the fuse. You have shut off the power to the whole trailer (assuming you do not have it plugged into shore power).

Good advice for listening for sparks = good controller. Checking for propane at the stove/water heater. The only thing left is the sail switch which requires a pretty good battery to generate enough fans speed to tell the controller to turn on the gas.

[Larry-NC]

Originally Posted by jhenretta

we disconnect the battery when the trailer is not in use yet still had the same issue the last time we used it. would disconnecting the battery be the same as pulling the fuse to reset the safe mode?

If your thermostat is the old mechanical type with a switch that says
Heat-Off-Cool, you just have to turn it to Off, then back to Heat, to reset the control. No need to mess with fuses.

Larry

[Larry-NC]

Originally Posted by UT_Grandpa

Disconnecting the battery either by the disconnect switch or pulling the negative lead is the same as pulling the fuse. You have shut off the power to the whole trailer (assuming you do not have it plugged into shore power).

Good advice for listening for sparks = good controller. Checking for propane at the stove/water heater. The only thing left is the sail switch which requires a pretty good battery to generate enough fans speed to tell the controller to turn on the gas.

That's NOT the only thing. Everyone points to the sail switch because that's the only part they understand. If you hear sparking, the sail switch is fine.

Another common point of failure is the propane regulator, mounted by the tanks. If it's not exact, the water heater and range will work fine, but the finicky Suburban furnace will not ignite. I built a gauge to test the regulator, pictures on request.

Larry

[CHICKDOE]

show the pictures of the gauge. i'm guessing a u-shaped tube to measure 11" water column.

[jackhartjr]

I have noticed that in most of these cases, the culprit was a battery not fully charged.

[dbledan]

Originally Posted by Larry-NC

That's NOT the only thing. Everyone points to the sail switch because that's the only part they understand. If you hear sparking, the sail switch is fine.

Another common point of failure is the propane regulator, mounted by the tanks. If it's not exact, the water heater and range will work fine, but the finicky Suburban furnace will not ignite. I built a gauge to test the regulator, pictures on request.

Larry

Yes...this.

On mine the sail switch was fine and it would spark. I got propane out of the stove no issues. Sometimes the furnace would light.

The key for me was when water heater kicked on they would both sputter sometimes. Then one day no furnace no matter how much I reset it. The water heater and stove worked fine. I swapped the regulator and it worked. When I changed over tanks I also found a bad pigtail to one tank. Single appliances worked fine but not multiple until I swapped the regulator.

[dustman_stx]

Originally Posted by Larry-NC

That's NOT the only thing. Everyone points to the sail switch because that's the only part they understand. If you hear sparking, the sail switch is fine.

Another common point of failure is the propane regulator, mounted by the tanks. If it's not exact, the water heater and range will work fine, but the finicky Suburban furnace will not ignite. I built a gauge to test the regulator, pictures on request.

Larry

I built a tube style manometer as well. Also have a dial type. And the sail switch is most definitely not the only part I understand. But it's a pretty common culprit- especially if you hear no attempt to open the gas valve and ignite- which the OP should easily be able to hear.

[MR.M]

Lots of things that could be the problem , mentioned so far , sail switch if unit sparks knock it off the list along with the hi limit , if it does not spark , could be low battery if not on shore power , bad board , sail switch or hi limit , if it fires and goes out , gas pressure check regulator , check igniter clean off any carbon build up, replace board , look for wasp nests , replace igniter , . sparks but no ignition check good gas pressure check gas valve coming on should be able to smell gas if not bad valve or board or bad igniter even if you hear a spark the igniter could be bad . igniter gap to big , burner burnt out this is mostly on older units . . I'm sure i left out a few things but if you get through all of these come back with your results

[Larry-NC]

Originally Posted by CHICKDOE

show the pictures of the gauge. i'm guessing a u-shaped tube to measure 11" water column.

Sure, here are the pictures. I built this out of scrap wood and Romex staples I had laying around, following directions from some RV website or other. The tubing and two fittings came from Lowe's. Total cost was under $5.

Your sharp eye will observe that although I've numbered in inches, the scale lines are actually 1/2" apart. This is because each inch of water column pressure pushes one side down 1/2" and the other side up 1/2".

The fittings are a little hard to see. One is a Nylon barb to IP fitting. The other is a brass IP to flare fitting. The flare fitting couples directly to the copper tubing uncoupled from the furnace.

I've filled it with water and a drop of blue food coloring for visibility. In a pinch I could have used coffee or tea.

Once I built it and used it, I was kicking myself. The Suburban maintenance manual says the first thing to do is check the pressure. I skipped that step and wasted a lot of time checking other things because I didn't have a gauge. After wasting a lot of time, I built the gauge, diagnosed the regulator, and had it going quickly.

And the nice thing about this one (unlike the dial gauges) is that it never goes out of calibration unless the force of gravity or specific gravity of water suddenly changes.

Larry

[MR.M]

Originally Posted by CHICKDOE

show the pictures of the gauge. i'm guessing a u-shaped tube to measure 11" water column.

Better and smaller to just get either the dial WC gauge or a digital one .that way you get all the fitting needed can test wc before and after gas valve etc

[jackhartjr]

Has the battery been checked to be sure it has a full charge?

[dustman_stx]

Originally Posted by MR.M

Better and smaller to just get either the dial WC gauge or a digital one .that way you get all the fitting needed can test wc before and after gas valve etc

Those have to be confirmed/calibrated using a U-tube manometer like shown above.