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Bourbon County · 02-21-2022, 02:42 PM

Does anyone know what year Keystone started putting the racetrack duct system in their RVs? I have a 2017 model 3661RL Montana.

My unit has 2 ACs and apparently blow their supply side air into 2 common ducts, one on either side of the coach. I tried looking with my bore scope and really can't really see anything but duct insulation. I also turned both ACs on and tried using my thermal camera to find the ducts, with no success there either. Fortunately this does mean there are no duct leaks of any consequence.

I understand the idea behind the duct configuration; since the rear unit is a heat pump, it can blow warm air throughout the coach and on milder summer days possibly 1 unit could maintain temperature or if one unit happened to be out you still have some cooling.

The best I can tell, the racetrack design attempts to keep the air blowing in the same direction regardless if one or both units are on; sounds good in theory. I know Grand design has 1 or sometimes 2 crossovers in their racetrack ducting. My question is if you have 2 units separated by 30 feet or so and an AC on either end blowing in different directions towards each other, wouldn't that just create a lot of turbulence in the duct system between the 2 units?

I did a high tech test on airflow direction using a strip of paper. I removed a supply diffuser in the (front) bedroom and turned the fan on for that unit, the rear unit was off. The air was blowing towards the rear of trailer as I expected. Repeated the test with front unit off and rear unit fan on high, the air in same spot was definitely towards the front of the coach as I expected. I then turned the fans on both units on HI and the airflow was still flowing towards the front of the coach.

I'm not from HVAC background but have had training on residential duct systems and air balancing. One of the enemies to airflow and killer to AC systems is static pressure. Is my thinking wrong that this configuration would just add a lot of back pressure when both systems are running?

02-21-2022, 02:42 PM	#1
Bourbon County Montana Fan Join Date: Feb 2022 Location: Cynthiana Posts: 202 M.O.C. #30449	Racetrack duct Does anyone know what year Keystone started putting the racetrack duct system in their RVs? I have a 2017 model 3661RL Montana. My unit has 2 ACs and apparently blow their supply side air into 2 common ducts, one on either side of the coach. I tried looking with my bore scope and really can't really see anything but duct insulation. I also turned both ACs on and tried using my thermal camera to find the ducts, with no success there either. Fortunately this does mean there are no duct leaks of any consequence. I understand the idea behind the duct configuration; since the rear unit is a heat pump, it can blow warm air throughout the coach and on milder summer days possibly 1 unit could maintain temperature or if one unit happened to be out you still have some cooling. The best I can tell, the racetrack design attempts to keep the air blowing in the same direction regardless if one or both units are on; sounds good in theory. I know Grand design has 1 or sometimes 2 crossovers in their racetrack ducting. My question is if you have 2 units separated by 30 feet or so and an AC on either end blowing in different directions towards each other, wouldn't that just create a lot of turbulence in the duct system between the 2 units? I did a high tech test on airflow direction using a strip of paper. I removed a supply diffuser in the (front) bedroom and turned the fan on for that unit, the rear unit was off. The air was blowing towards the rear of trailer as I expected. Repeated the test with front unit off and rear unit fan on high, the air in same spot was definitely towards the front of the coach as I expected. I then turned the fans on both units on HI and the airflow was still flowing towards the front of the coach. I'm not from HVAC background but have had training on residential duct systems and air balancing. One of the enemies to airflow and killer to AC systems is static pressure. Is my thinking wrong that this configuration would just add a lot of back pressure when both systems are running?