Roof ACs Not Cooling While Driving - Work GREAT Parked

[Hittntheroad]

I think you will find part of the problem is heat penetration from areas in the rv that are not air tight.
I have been slowly finding all the areas in my Thor Ace 30.1 where outside air is getting. It's impossible to keep it airtight but some places are so obvious and easy to fix.
One in particular on mine was the A pillars, I believe they are called are like a duct leading from the front grill area to the top inside the coach. I know on mine they are hollow and lead to the inside because I ran a positive and negative wire from the battery to the inside roof area of my coach to power my led awning lights. I filled the top area with fiberglass insulation. Optimum would have been from the bottom but couldn't get acces with my hand to put the insulation there.

[Hittntheroad]

In this picture you can see the red and black wires I ran from the battery in the grill area.
Has to be like a ram air induction.
You can also see where I have been insulating the fiberglass cap on the front of the rv.

[mel s]

Originally Posted by f15epilot

Searching for opinions here.

PROBLEM: My new (to me) Travel Supreme 42ME coach came with dual 15kBTU Penguin Duo-Therm heat pumps. Sitting parked, on generator or shore power, they will cool the coach down to <68 in 95-F ambient full sunshine. Driving down the road, though, they simply do not cool. The air coming out of the vents is >75-F and that allows the interior WHILE DRIVING to eventually become unbearable in 90+ ambient conditions.
From reading multiple other posts, there seems to be a disparity in performance between Class A roof-top AC systems while in motion: some work great moving or sitting still (like my Damon Outlaw's did); others only seem to work sitting still (like these Penguin Duo-Therms).

QUESTION: Why? What is causing the difference in performance and better...what can be done about it (if anything).

Originally Posted by Old Scout

OK--first thing to understand is that the 20-25 degree A/C differential is a measure of ambient INSIDE air going into the air box vs cooled air leaving the dash vent--eg, if your inside ambient air is at 90, you should expect cooled vent air to be at 65-70. As your cab cools to 80, then vent air should drop to 55-60. Accordingly, if you draw in outside air rather than recirculating inside air [eg, set controls on "Max"] you are always trying to cool 90 outside air. Good points were made about air leaks in the ceiling duct work, and under the roof shrouds that allows warm and cool side air to remix. On really hot days, we added a shower curtain [designer if you like] hung behind the driver/pass seats--yes, rest of coach gets/stays warm but cab area does fine with just dash A/C. Ironically, some of this also applies to winter dash heating. Use max cool setting but set heat knob to hot--this will recirc and heat only inside air. Also many coaches are designed with front caps and aerodynamic dams that create a partial vacuum in the area where the dash heater is attempting to draw air--in this case you will notice that the heater works great while stopped or driving thru towns, but degrades at hi-way speeds.

Old Scout
That is an excellent explanation of the short comings of dash A/C and dash heater operation in motor homes.

However the OP is asking about what he considers to be inadequate interior cooling provided by the "dual 15kBTU Penguin Duo-Therm heat pumps" on his Travel Supreme 42ME while driving in hot weather.

Mel
'96 Safari

[Waiter21]

I don't think air circulation around the A/C cowling is the issue, but I had some thoughts of tufting the cowl and tape a GoPro to the top of the satellite dish to record the tufts.

As someone else mentioned, operate your dash A/C in "MAX" mode, this closes off the outside air and recirculates inside air.

On my Mirada, I also found several significant air leaks that were allowing outside air to enter from around the firewall and engine cowling. These made a HUGH difference in cooling during the summer drive.

[Old Scout]

Mel-- agree with your assessment. Several of the responses went off track by combining dash and roof-top issues--me too. Anyway, I couldn't think of any reasons to explain what the OP was experiencing so kind of launched a "any and all things about RV A/Cs discussion," which included outside air leaks and the mixing of hot and cooled air in the ducts and under the shroud. Again, doesn't explain why the OP's roof-tops don't seem to work as well while driving but based on vent output deltas, the effectiveness of both the dash A/C and the roof top units, ultimately impact on inside ambient air temps and the perceived or measured temperature of the cooled air leaving the vents--dash or roof-tops.

[TexasTom]

I have the same units, and used to have some performance issues while driving as well.

Here is how I fixed mine. Pull off the shroud and take off the metal cover on the front side of the unit. I found the insulation was inadequate and is some places gone. As an engineer you will see why it is an issue. Put a good quality insulation back in and see if that helps.

[Slice]

Read same issue somewhere else. There is a known issue of this in certain units. The fix has to do with deflection of housing going. Down the road at 60 mph and the condenser fan blades not moving enough air thus not cooling very well. Mine I have no issue.

[bruceisla]

Originally Posted by Slice

Read same issue somewhere else. There is a known issue of this in certain units. The fix has to do with deflection of housing going. Down the road at 60 mph and the condenser fan blades not moving enough air thus not cooling very well. Mine I have no issue.

If this were the case, the measurement of the warm/cold delta would show it.

[bluepill]

Also possible that the thermostat is being washed in cold air while at speed and cutting off too soon. Might want to use a wired indoor/outdoor thermometer with an external probe and min/max memory to check it.

Don't forget to inspect behind the thermostat to make sure that the hole for the wiring is properly sealed.

If you have an EMS panel that reads amps, check the reading to make sure that the compressors are not cutting out while driving.

[tkcas01]

If your units are ducted, consider that there may be some issues with the integrity of the ducts within the ceiling. There is a possibility that outside air is being forced into breaches in your ducts while underway.

Here is a recent response I had to a post reporting similar issues. You can also look at other posts on the thread to see what others said.

http://www.irv2.com/forums/f115/when...ml#post3185938

[f15epilot]

Lots of good responses. I am particularly keen to investigate under the shrouds of the A/C units. Some things to discount from some posts:
1) Thermostat 'awash'...in the TS, the control is in the bathroom (in a cabinet); the sensors for zone 1 and zone 2 are afixed to the walls in the front cabin/rear bed room. The front cabin sensor is on the wall forward of the slide and behind the seats. In that position, it is actually in a warmer position as it is not in the airflow.

2) Ducts leakage. Fiberglass roof with no leaks on all sides/top; and 6" of insulation in the roof surrounding the vents. Plus, DW checked airflow out of ducts after A/Cs were off. If there were 'leaks', then there would be warm air flowing as we were still driving. The vents are partially obstructed on one side (drivers) main cabin, but most are not. The air just is not as cool as when sitting still. And at slower speeds (around town), the cooling is notably better.

3) Use of max vs. vent. We were using 'max' on the dash system; all windows and vents closed; no notable air 'rush' sounds that would indicate leakage.

Looking at the shrouds, and noting that the 'new' design has holes and a more aerodynamic shape to create airflow 'out' from under the shroud, I believe there is an issue there. Otherwise Penguin (Dometic) would not have changed the design. When the coach is returned with a working A/C in the dash (I'm hopeful the guys from Spartan and my local shop, working together, solved that perplexing issue), I hope to do some Go-Pro/wind tuft work on the top.

I learned in my prior life never to underestimate the impact of small physical changes on aerodynamic forces. On the F-15, there is a small metal cap on the very nose held in place with a screw. If that cap is off-center by even a 1/2-inch, or if there is any imperfection in the first 11-inches of the nose, the resulting vortex it creates is sufficient to cause upwards of 11 tons (22,000 lbs) of side force on the tail of the aircraft, pushing the aircraft 'sideways' at the tail and causing it to depart at slow speeds.

More as I get the info...thanks for the responses.

[bruceisla]

Originally Posted by f15epilot

Lots of good responses. I am particularly keen to investigate under the shrouds of the A/C units. Some things to discount from some posts:
1) Thermostat 'awash'...in the TS, the control is in the bathroom (in a cabinet); the sensors for zone 1 and zone 2 are afixed to the walls in the front cabin/rear bed room. The front cabin sensor is on the wall forward of the slide and behind the seats. In that position, it is actually in a warmer position as it is not in the airflow.

2) Ducts leakage. Fiberglass roof with no leaks on all sides/top; and 6" of insulation in the roof surrounding the vents. Plus, DW checked airflow out of ducts after A/Cs were off. If there were 'leaks', then there would be warm air flowing as we were still driving. The vents are partially obstructed on one side (drivers) main cabin, but most are not. The air just is not as cool as when sitting still. And at slower speeds (around town), the cooling is notably better.

3) Use of max vs. vent. We were using 'max' on the dash system; all windows and vents closed; no notable air 'rush' sounds that would indicate leakage.

Looking at the shrouds, and noting that the 'new' design has holes and a more aerodynamic shape to create airflow 'out' from under the shroud, I believe there is an issue there. Otherwise Penguin (Dometic) would not have changed the design. When the coach is returned with a working A/C in the dash (I'm hopeful the guys from Spartan and my local shop, working together, solved that perplexing issue), I hope to do some Go-Pro/wind tuft work on the top.

I learned in my prior life never to underestimate the impact of small physical changes on aerodynamic forces. On the F-15, there is a small metal cap on the very nose held in place with a screw. If that cap is off-center by even a 1/2-inch, or if there is any imperfection in the first 11-inches of the nose, the resulting vortex it creates is sufficient to cause upwards of 11 tons (22,000 lbs) of side force on the tail of the aircraft, pushing the aircraft 'sideways' at the tail and causing it to depart at slow speeds.

More as I get the info...thanks for the responses.

You could email Dometic and ask why they added holes.

[f15epilot]

Trying to figure out to whom at Dometic to direct the inquiry is a challenge. Large company...difficult to find someone knowledgeable of the shroud design AND able to talk about it (if the design change addresses a defect in the original design, their legal team will caution against discussing the rationale).

Mine is a rather unique coach to start as a mid-engine RV; and apparently it was both the first mid-engine chassis used for an RV and the first Travel Supreme ME built, making it more unique. The leveling system, for example, is powered by the coach hydraulic system with a pick-off at the power steering unit (no separate reservoir). Neither Spartan nor Lippert (LCI) tech support ever heard of such an install and cannot figure out how it was done.

Still, I've sent Dometic an inquiry. We'll see where it goes. Looking forward to looking under the cowls when I get it back from the shop, hopefully tomorrow.

[mel s]

f15epilot
Unfortunately methinks you may find that "It is what it is".

You may have to except the fact that the air conditioners on your coach, (like those on most coaches), cool the coach interior better when the coach is sitting than they do while the coach is moving/traveling.

Mel
'96 Safari