Thor Rooftop A/C not keeping up with heat

[Cwray]

I don’t recall the measurements for insulation, sorry. For the copper pipe, it was roughly a foot or so and I just used a pool noodle that I had laying around.

If I had to do the insulation over again, I’d do it a bit differently. I’d either apply the insulation to the plastic cowling all over (end up using much more admittedly), or just do that on the side of the aluminum shroud that has the access panel.

You might need to get into there for a repair, and pulling off the tar paper and foam insulation is a real pain (and you might end up destroying that stuff as you yank it off). As it turned out, we decided to also install soft-starts to allow us to run the AC units without 50amp connection or the genny. So, I speak from experience on taking that stuff off. But, Glad we did, as now I can get both 15K units on when just plugged into a standard 20Amp circuit in my garage. I ended up replacing the insulation on that side, as a result.

Btw, doing the internal and external insulation work has the added benefit of making your AC units quieter as well.

[jabrabu]

I have a 15K A/C unit on my 32 ft. class C, which is now about 4 years old. It used to cool well, even in very hot weather, but on our last trip it would only cool about 10 degrees below the outside temperature.


I plan to clean the condenser, but I'm not sure what else would keep it from working like it used to. I've heard that you can't recharge the freon in these. Is that true?

[Beau388]

Originally Posted by jabrabu

I've heard that you can't recharge the freon in these. Is that true?

Well, the roof A/Cs do not have service ports like your home A/Cs. That said, there are line taps available for the do-it -yourself guy. I doubt than any reputable firm would recommend refrigerant service on a roof A/C.

To service the unit correctly, a die needs to be injected into the refrigerant. Once the leak is found, the system is pumped down and the leak repaired. Next the system is pressure, leak checked and vacuum leaked check. Finally. the exact weight of the refrigerant recommended is added.

Is that expensive? - yes. Does it always work - no.

[chunker21]

A few times in this and other threads I have seen the comment to take the front and rear vents off and inject foam or otherwise block off the end of the air conditioning ducting. Those statements back it up with why cool the end caps of the unit. My thought was why on earth would any RV manufacturer have an open end ducting? I pulled the 2 front and rear duct vents and see that mine are not that way. The styrofoam ducting goes a bit beyond the vent and stops. 8" in front, 12" in back. I do see a possible problematic issue up front in that the front vents are beside the non-powered ceiling vent. The foam ducting is cut so that the ceiling vent box is right there and on the forward edge it appears that the open path from side to side is there along with the vent aluminum "box". In the rear, no such compromise and both the left and right a/c ducting ends abruptly and cleanly 12" aft of the a/c vents. No crossover side to side.

Couple other notes. I pulled the complete ceiling section off the rear air and it could use the benefit of taping to streamline and seal airflow. But the thermistor on the aft unit is 4" up, not near the bottom like the one long post stated. So for me I see no advantage to moving the thermistor up and in the rear no benefit from adding a foam dam to the a/c ducting.

I'm running both units with the front going to the ducting and rear of course wide open down. I have a couple of thermometers in the mid hall ceiling a/c vent.

[RCS]

Just finished boxing in the AC vent area - just like the video that Greybear linked to. It was not difficult at all. The hardest part for me was peeling the paper backing off the foil tape. I taped up all the edge openings and tried to smooth the air flow as much as I could. I used my table saw to cut the foam board, clean and easy.

My thermistors are at the very top of the unit - I left them there for now.

I also plan to put some insulation around the outside of the condenser unit. One step at a time.

[chunker21]

Originally Posted by chunker21

A few times in this and other threads I have seen the comment to take the front and rear vents off and inject foam or otherwise block off the end of the air conditioning ducting. Those statements back it up with why cool the end caps of the unit. My thought was why on earth would any RV manufacturer have an open end ducting? I pulled the 2 front and rear duct vents and see that mine are not that way. The styrofoam ducting goes a bit beyond the vent and stops. 8" in front, 12" in back. I do see a possible problematic issue up front in that the front vents are beside the non-powered ceiling vent. The foam ducting is cut so that the ceiling vent box is right there and on the forward edge it appears that the open path from side to side is there along with the vent aluminum "box". In the rear, no such compromise and both the left and right a/c ducting ends abruptly and cleanly 12" aft of the a/c vents. No crossover side to side.

Couple other notes. I pulled the complete ceiling section off the rear air and it could use the benefit of taping to streamline and seal airflow. But the thermistor on the aft unit is 4" up, not near the bottom like the one long post stated. So for me I see no advantage to moving the thermistor up and in the rear no benefit from adding a foam dam to the a/c ducting.

I'm running both units with the front going to the ducting and rear of course wide open down. I have a couple of thermometers in the mid hall ceiling a/c vent.

I worked on both units yesterday evening and did the following. Both thermistors were about 4" up so I left them in place. The 2 front vents where the styrofoam ducting was "shared" or compromised by the front vent, I used a can of expanding foam to seal off the ducting where it appeared to be compromised by the vent installation. If/when I pull the front interior panels to boost insulation in the cabover, I'll probably find a bunch of the foam that shot too far forward for this particular job. The divider panels on both between the intake and exhaust air, was in pretty good shape but I taped them with the foil tape to properly secure them with more than just friction of the foam strips on them. I used strips of foil tape to make the entrance to the ceiling ducting more "aerodynamic" and reduce potential turbulence of the airflow. Taping to clean up the areas and block any potential leaks of cooled air.

I didn't see any need to add any foam or ducting blocking on the rear unit since the integrity of the ducting was good and it ended about 12" from the ceiling vent. As I was starting this I put a thermometer into a central ceiling duct and was reading 60*. Not sure that has any validity to previous discussions as I'm parked under a pole barn but the setting sun was getting on the front. Deep South and clear skies yesterday outside temps low 90s to upper 80s. No pictures of the work since access was difficult to see and the taping doesn't look any difference from the previously posted videos.

[Judge]

There is a lot of mis-information about the "thermistors" in some threads out there.

This is actually a Freeze Sensor Switch. Some people recommened removing them and letting them dangle free. Others posted about exact position placement.

They should be inserted into about the center of the evaporator coil. They sense if ice begins building up in the evaporator coil. If it does, the sensor shuts off the compressor.... but allows the fan to run while the ice melts. Then it allows the copressor to cycle back on.

When the sensor is dangling free and can't detect ice build-up, the compressor will just run until there is no airflow because the evaporator coil becomes a block of ice and air can't pass through it.

[chunker21]

Originally Posted by Judge

There is a lot of mis-information about the "thermistors" in some threads out there.

This is actually a Freeze Sensor Switch. Some people recommened removing them and letting them dangle free. Others posted about exact position placement.

.

Agree so I left mine in place. Still want to know about the ducting and blocking the ducting recommendations from you and others. I think I read from you that you added foam to the front which based on what mine looked like, should be good. Others have comments about the rear also, but I'm not sure they have the Omni and perhaps other models just vent to the front and rear caps. There are posts about installing a powered vent fan in the Omni/Magnitude so I'm going to one of this threads and ask what they saw when they removed the existing non-powered vent.

Enjoy the trip and hopefully no issues arise that divert you to an RV sales lot. TS Ida, forecast to a Cat 3 will hit the gulf coast this weekend and that may interfere with my travels next week up to VA and WV. We'll see.

[Judge]

Originally Posted by chunker21

Agree so I left mine in place. Still want to know about the ducting and blocking the ducting recommendations from you and others. I think I read from you that you added foam to the front which based on what mine looked like, should be good. Others have comments about the rear also, but I'm not sure they have the Omni and perhaps other models just vent to the front and rear caps. There are posts about installing a powered vent fan in the Omni/Magnitude so I'm going to one of this threads and ask what they saw when they removed the existing non-powered vent.

Enjoy the trip and hopefully no issues arise that divert you to an RV sales lot. TS Ida, forecast to a Cat 3 will hit the gulf coast this weekend and that may interfere with my travels next week up to VA and WV. We'll see.

My front vents were open to where the front cap is mounted to the house box. My concerns was air leaking off to the sides in the ceiling and not just at the end of the ducts themselves. The same for the back vents.

I took a fine saw and cut the styrofoam under each vent to smooth out all of the jagged edges as well that Thor left behind to help the airflow.

I can say my overall airflow is better than stock now. Also, adding the RV Airflow insert to the front unit helps push more air to the bedroom vents. Since I added that upgrade we have not had to run the rear A/C at night... even when it was mid-90's during the days and mid-70's at night in Nashville.

[Rickszat@gmail.com]

We have a Thor 2020 Delano FB (Class C diesel - Mercedes Sprinter chassis)). We do the nightly cool down, shades down, cab windows covered, etc. (that everyone is suggesting) and have dual pane windows.

In extreme situations, we start the rig's engine and run the cab AC at full blast, aiming the vents into the back of the rig. Since the rooftop AC does provide ~15 degree cooling (as people noted), getting the ambient temperature down using the rig's AC helps.

[chunker21]

Originally Posted by Judge

My front vents were open to where the front cap is mounted to the house box. My concerns was air leaking off to the sides in the ceiling and not just at the end of the ducts themselves. The same for the back vents.

I took a fine saw and cut the styrofoam under each vent to smooth out all of the jagged edges as well that Thor left behind to help the airflow.

I can say my overall airflow is better than stock now. Also, adding the RV Airflow insert to the front unit helps push more air to the bedroom vents. Since I added that upgrade we have not had to run the rear A/C at night... even when it was mid-90's during the days and mid-70's at night in Nashville.

Judge see my new thread about Omni air conditioners.

[LarryD]

Judge, you need to open an RV shop.

[LarryD]

Havent scoped it yet but this cant be good.... I have one like this up front also.

[kwplot34]

Originally Posted by LarryD

Havent scoped it yet but this cant be good.... I have one like this up front also.

Attachment 33120

That is quite the blockage you have there. Take the vent down and see if you can remove it.

[abjbrtd]

Originally Posted by chunker21

A few times in this and other threads I have seen the comment to take the front and rear vents off and inject foam or otherwise block off the end of the air conditioning ducting. Those statements back it up with why cool the end caps of the unit. My thought was why on earth would any RV manufacturer have an open end ducting? I pulled the 2 front and rear duct vents and see that mine are not that way. The styrofoam ducting goes a bit beyond the vent and stops. 8" in front, 12" in back. I do see a possible problematic issue up front in that the front vents are beside the non-powered ceiling vent. The foam ducting is cut so that the ceiling vent box is right there and on the forward edge it appears that the open path from side to side is there along with the vent aluminum "box". In the rear, no such compromise and both the left and right a/c ducting ends abruptly and cleanly 12" aft of the a/c vents. No crossover side to side.

Couple other notes. I pulled the complete ceiling section off the rear air and it could use the benefit of taping to streamline and seal airflow. But the thermistor on the aft unit is 4" up, not near the bottom like the one long post stated. So for me I see no advantage to moving the thermistor up and in the rear no benefit from adding a foam dam to the a/c ducting.

I'm running both units with the front going to the ducting and rear of course wide open down. I have a couple of thermometers in the mid hall ceiling a/c vent.

"The styrofoam ducting goes a bit beyond the vent and stops. 8" in front, 12" in back. I"

The benefit from blocking the duct is smoothing the flow of air. The way it's built some/most of the air goes past the vent hits the wall swirls around and tries to get out the vent.
I measured the before and after air speed and was surprised to see a 1 to 2 mph improvement .
I recomend trying it, the ac tubing insulation was a perfect fit

[LarryD]

I now see how it looks like a blockage. Thats actually the inside of the duct work (no blockage) and somehow light is coming from somewhere lighting it up on the inside of the duct. I have no ide where the light is coming from yet but will use a boroscope to look as soon as I get back home.

[chunker21]

Originally Posted by LarryD

I now see how it looks like a blockage. Thats actually the inside of the duct work (no blockage) and somehow light is coming from somewhere lighting it up on the inside of the duct. I have no ide where the light is coming from yet but will use a boroscope to look as soon as I get back home.

As bright as it is, removing the vent and looking in there may tell you or a small mirror. I used an inspection mirror to investigate mine. Course on mine I also had to shine a light in there to see the gaps.

[ducksface]

the light in my rear duct comes from the bathroom skylight

[JimOIB]

All great advice. One item I found was hot air being pulled into the coach from under the slide. To stop this air penetration I used 1” foam pipe insulation to seal the gap under the slide. I cut them to length to seal the gaps - less than $10.00. My wife didn’t like the look so she made pinto bean filled draft-dodgers that do the trick.

The analogy is max A/C on your dash. It recycles air already cooled. When it isn’t on it draws air from the outside. Sealing the gap under the slide is like going from A/C to max A/C. Stuff a few towels under the slide and see what a difference it makes.

[LarryD]

there is duct work connecting the front and rear. Air was blowing thru the front unit duct even though it was turned off. Tested by turning rear on and off and proved that the rear blows air into the front. There also seems to be updates of making the unit more efficient. No gaps, nothing to seal, they even have their own version of the pyramid thing to isolate each side and make it more efficient. See attached photos.






So, put a front window cover, the kind that goes from passenger door window, over windshield then over drivers door window ($36 on Amz) and that alone made a nearly 10 degree difference.