Wrong type of upper vent?

[joshuajim]

My Dometic 2652 located in a slide has never cooled well. With the addition of fans I have been able to keep the refer temp around 40 degrees. All systems have been checked and properly serviced.

Today I was looking at the upper vent. I noticed that it is the same as the lower vent. On the lower vent, the air enters and then is directed upward as proper flow would dictate. BUT on the upper vent the air has to turn 180 degrees downward before exiting. This seems totally wrong. I understand that the vents are designed to keep rain out, but the airflow is totally inteuuupted as it tries to flow out.

In addition, it looks like the free area is considerably less than a typical roof vent.

I wonder if a different type of upper vent would aid the air flow.

[LarryJM]

ScottG wrote:
What you have is very normal.
Another thing that's normal is for RV manufacturers to ignore the installation instructions in ragards to clearances and flue baffling.
It would behoove you to pull the fridge and follow the install instructions to the letter.
Also, I would create a radiused or angled flue to smooth the flow of air out the upper vent rather than the hard 90 degree it probably has to make now.
If you can provide the chimney effect the manufacturer instructions describe and smooth the flow of air exiting the compartment, it will cool better.

These are EXCELLENT POINTS and in my two trailers I also found the installation with regards to baffling and clearances not to specs and poor.

A major discrepancy I found on both trailers is not properly sealing off the dead air space at the top of the refer which can form a "HOT AIR POCKET" and severly restrict air flow out of the top vent.

Larry

[dougrainer]

joshuajim wrote:
Doug
The "silver metal plate" is a factory install by FR. I tried the 4" higher fan location first as indicated by the patches in the photo. The lower location seemed to work better. The distance between plate and back is 2.5".

I'll pull the refer one more time (got it down to less than 8 minutes). cut the plate and relocate the fans to the back. Would about and inch spacing off the back wall seem about right?

I might mention that when running the "exhaust" air is about 113 degrees vs 92 at the bottom inlet.

FR, That does not mean good things. FR screws up more refer installs than all other OEM's combined. Yes, do the modification. You need to get as much air THRU the Condenser fins as possible to remove the heat. Doug

[joshuajim]

Doug
The "silver metal plate" is a factory install by FR. I tried the 4" higher fan location first as indicated by the patches in the photo. The lower location seemed to work better. The distance between plate and back is 2.5".

I'll pull the refer one more time (got it down to less than 8 minutes). cut the plate and relocate the fans to the back. Would about and inch spacing off the back wall seem about right?

I might mention that when running the "exhaust" air is about 113 degrees vs 92 at the bottom inlet.

[dougrainer]

joshuajim wrote:
Here ya go.


Click For Full-Size Image.

OK, your modification is not correct. The fans need to be about 4 inches higher and not pulling air where they are. That silver metal plate needs to STOP even with the top of the Condenser fins. Then just mount the 2 fans to the back wall of the refer just below your curved upper radius. What is the width between the radius vane and the metal mount plate the fans are mounted too? Doug

[time2roll]

If it is that tight one fan would be fine. Is the performance just as bad on propane? Or have you checked the heater assembly looks good and is clear of obstructions? Otherwise if the thermostat is set to full cold and performance is bad then I agree it might be time for a compressor.

[joshuajim]

time2roll wrote:
I would be interested to see the gap between the wall and the tubing.
Should be very tight or have a baffle to force all air over the tubes not just up the side.

With added insulation I am 0-0-0 top, side and back.

[joshuajim]

bigfootford wrote:

dougrainer wrote:

joshuajim wrote:
OP here. I've made the installation match to a T and even added the radiused baffle at the top, 3 fans on the evaporator and 2 fans sucking at the top and one on the interior fins. Maxed out the perimeter insulation and the door seal is good. I think I just got a bad refer from the get go.

I still think that the upper vent is poorly designed. Hot air like to rise but when it hits the upper grill it has to desend and then meets cooler outside air which is denser. Not a good design. Probably works on most units but could be better.

My unit has been running all day on direct connect electric and it still is only 42 with OAT at 92.

In a slideout, you need to have at least 1 fan blowing straight out that upper door. Can you post a pic of the upper hole showing the back of the refer. I want to know how high up the condenser fins are in relation to the door cut out. Doug

Measure the voltage right at the 120vac plug for the fridge. An extension cord, rigs wiring could cause the 120vac to be 110 or less. That heating element will not be performing to spec.
A loss of 30+ watts is significant.

A Bud was having trouble.... He found that his water heater 2 way was on along with a small space heater and he had a 50ft 14ga extension cord... 105vac at the fridge..

Jim

My voltage varies from 124 in the early morning to 117 in the afternoon when regional A/C demand is high. I'm a licensed general contractor for 39 years, so I generally can avoid the common problems. None of my extension cords are less than 12 Ga and some are 10.

Note in my post that I was direct connect to the heater bypassing the refer controls.

[time2roll]

I would be interested to see the gap between the wall and the tubing.
Should be very tight or have a baffle to force all air over the tubes not just up the side.

[joshuajim]

Here ya go.


Click For Full-Size Image.

[bigfootford]

dougrainer wrote:

joshuajim wrote:
OP here. I've made the installation match to a T and even added the radiused baffle at the top, 3 fans on the evaporator and 2 fans sucking at the top and one on the interior fins. Maxed out the perimeter insulation and the door seal is good. I think I just got a bad refer from the get go.

I still think that the upper vent is poorly designed. Hot air like to rise but when it hits the upper grill it has to desend and then meets cooler outside air which is denser. Not a good design. Probably works on most units but could be better.

My unit has been running all day on direct connect electric and it still is only 42 with OAT at 92.

In a slideout, you need to have at least 1 fan blowing straight out that upper door. Can you post a pic of the upper hole showing the back of the refer. I want to know how high up the condenser fins are in relation to the door cut out. Doug

Measure the voltage right at the 120vac plug for the fridge. An extension cord, rigs wiring could cause the 120vac to be 110 or less. That heating element will not be performing to spec.
A loss of 30+ watts is significant.

A Bud was having trouble.... He found that his water heater 2 way was on along with a small space heater and he had a 50ft 14ga extension cord... 105vac at the fridge..

Jim

[dougrainer]

joshuajim wrote:
OP here. I've made the installation match to a T and even added the radiused baffle at the top, 3 fans on the evaporator and 2 fans sucking at the top and one on the interior fins. Maxed out the perimeter insulation and the door seal is good. I think I just got a bad refer from the get go.

I still think that the upper vent is poorly designed. Hot air like to rise but when it hits the upper grill it has to desend and then meets cooler outside air which is denser. Not a good design. Probably works on most units but could be better.

My unit has been running all day on direct connect electric and it still is only 42 with OAT at 92.

In a slideout, you need to have at least 1 fan blowing straight out that upper door. Can you post a pic of the upper hole showing the back of the refer. I want to know how high up the condenser fins are in relation to the door cut out. Doug

[wa8yxm]

There is a limit to how much "Cool" an absorption cooling system can provide. If it's too hot out. and too hot in and the sun is beating down on it. You may have an issue.

Adding cooling fan(s) may help.. Mine is in the lower compartment blowing UP. I have a single Computer type fan (4") in the compartment. Tight fit. I may put in a 2nd one later. Blowing UP through the condenser and out the top. Mine is not in a slide so it blows out the roof. You can also put 'em in the top sucking air. but I like it better in the bottom where I don't have to climb a ladder.

[fred42]

Does your unit have that sliding piece of plastic on the inside that is supposed to be a thermostat?

[joshuajim]

OP here. I've made the installation match to a T and even added the radiused baffle at the top, 3 fans on the evaporator and 2 fans sucking at the top and one on the interior fins. Maxed out the perimeter insulation and the door seal is good. I think I just got a bad refer from the get go.

I still think that the upper vent is poorly designed. Hot air like to rise but when it hits the upper grill it has to desend and then meets cooler outside air which is denser. Not a good design. Probably works on most units but could be better.

My unit has been running all day on direct connect electric and it still is only 42 with OAT at 92.