Grand Design furnace short cycling problem

[Mattgg]

My problem doesn’t sound like it pertains to yours but I thought I would throw it out there. I though I had a similar problem at first. I have a 2019 GD 3000QB, I have a vent that blows directly onto my thermostat from about 4 feet away, it’s not the type that I can close, and spinning it to change the direction doesn’t help because it is so close to the furnace that it blows out with too much force. So it blows on the thermostat no matter what (warm air rises to the chest high thermostat.) Which leads to the obvious problem that the camper stays very cold and the furnace blows for about a minute, heats up the thermostat and then shuts off. Then after about 3 minutes when the thermostat cools down the cycle starts over again. Very Shitty design.

[packerprogrammer]

I am leaning towards airflow still. Consider that when the unit is installed in the RV it is basically inside a box. Any heat that isn't exhausted is contained in that small area. If you have facebook you can see we have been discussing this issue recently. Only one person has a short cycling issue, but all of us have heating issues. If you read the manual for the furnace, the minimum duct requirement is not met from the factory and personally I think air leaks in the plenum and the confined space lead to over heating. You would think that the manufacturer could tell you which limit switch is kicking the furnace off. I'm guessing it's the high heat switch. Here is a link to one of the facebook discussions. You will have to join the private group. https://www.facebook.com/groups/2701...5455872036855/

[nomadlife]

I think this is a great idea! I will do that and report back. We check the gas presure and it reads 11 WC.

Did you replace the regulator on rig? I swapped the original for the auto/switch regulator and it solved problems I didn’t know I had. I note your bench test on original unit worked. I also note you bypassed the propane of the unit installed which would not prove regulator, but if you try to run the furnace on an empty tank a similar situation happens, it just never reignites. Meaning regulator may not be providing sufficient fuel and furnace recognizes this? Wishing you resolution and sad to hear GDRV is bowing out before your satisfied.

-not an expert

[Martin Russell]

Hi we have a new 303 we were out the first week trying our new unit. l was laying in bed one morning and noticed that the furnace started and ran great for 3-4 minutes then l heard burner cut off and a after a couple of minutes burner fired again. I have been in the HVAC business for 50 years and new right off there was an issue with the air flow. First thing l checked was the return air to make sure there was enough free area. Then l googled the furnace in our unit to see what was the recommended air flow for that furnace and got the sq in area recommended. I checked the ducting attached to the furnace which for ours was a total of 3-4” and 1-2”
The furnace was sitting over the one duct with 2-4” holes there was a 2” flex routed to the basement and an additional 4” flex attached to the duct running forward. When l Removed this flex I found the duct was flattened and almost totally restricted l repaired and added an additional 4” which was required to make the recommended requirement for air flow. Unit works perfectly now.
Good luck

[dthiem2002]

I’ll add my two cents. Our 2800bh also had a vent that blows right at the thermostat. It cycled every few minutes. I checked for flat ducts, return air obstructions etc. I removed a lot of the cabinetry to see the duct work...in the end, I solve it by replacing the register facing the thermostat with a dryer vent hood that directs the air into the main cabin away from the thermostat. Problem solved instantly with that fix.

[fez111]

We checked all ducts and even added another two 4" ducts and it still does the same thing. Then, we pulled the unit out and it did the same thing on a bench test. finally We received a new unit from AirExcel and....it does the same thing! What else could it be?

Just a thought... As far as ducts, have you checked the cold air return...as in kinks in the flexible pipes in the belly? Restricted airflow is not limited to the heat outlets. If there's not enough air coming in its the same scenario... 2c.

[FreddieD]

Assuming you still have the issue, I noted on your test the unit was laying on its side, is that how it sets in the rv? Also one other thing to check would be extend the thermostat control to the bench and see how the removed working unit operates connected to the RV's thermostat.

[Brady23PNW]

Any luck getting this fixed?
Is it the lack of ducting?

[Skiddy]

Just a thought... As far as ducts, have you checked the cold air return...as in kinks in the flexible pipes in the belly? Restricted airflow is not limited to the heat outlets. If there's not enough air coming in its the same scenario... 2c.

Great point on checking the return air for restrictions. The unit was bench tested so it would be assumed that all air flow was unrestricted, yet it had the same short cycle on the burner. It is my understanding the benched unit still short cycles the burner wile the fan operates until the thermostat no longer calls for heat. I’m starting to think this is the way it works.

[Skiddy]

I’ll add my two cents. Our 2800bh also had a vent that blows right at the thermostat. It cycled every few minutes. I checked for flat ducts, return air obstructions etc. I removed a lot of the cabinetry to see the duct work...in the end, I solve it by replacing the register facing the thermostat with a dryer vent hood that directs the air into the main cabin away from the thermostat. Problem solved instantly with that fix.

Interesting you had to change the hot air vent. Our first furnace experience was similar, the vent in our kitchen cabinet, about two foot run from the furnace blew to the floor, just below the wall mounted thermostat. Short cycled the furnace. Our heat vents rotate so the air can be directed in your choice of 360º. I spun it to blow into the kitchen away from the thermostat location and it was much more comfortable.