Cooling

Roof Vent Fan and Air-conditioners

TIP#299: Cooling Tips – Before going on to describe the fan and air conditioners, we should let you know sprinter vans are very difficult to cool off in summer. There are several things you can do to help cool your van.

• Run the roof AC while driving – If you have the Li3 battery, about 1/2 to 1 hour before you arrive at your camp site, turn on the roof AC while driving. This will cold-sink the interior and give the roof AC a head start cooling the van instead of trying to cool a warm van once parked.
• Idle the Engine – After arriving at the campground, leave the engine idling for a few minutes to run the dash AC while you are hooking up the utilities. This will also give the turbo charger a few minutes to cool down.
• Open the hood – Once you’ve shut off the engine, open the hood to let the engine cool down quicker instead of holding all that heat next to the cockpit firewall.
• Install an external windshield cover. Blocking the heat before it can enter the windshield is better than trapping it inside like a greenhouse.
• Install a curtain behind the front seats to reduce the size of the air volume the roof air conditioner has to cool.
• If possible, park with the front of the van facing the sun, rather than heating a side of the van.
• If the sun is on the passenger side, extend the awning to shade the side. (Unfortunately, the powered awnings can’t be angled down to provide more shade like the manual crank awnings.)
• Use a sun screen mesh that attaches to the extended awning to shade the side of the van. Awning legs may be required to support the extra weight.
• Lower the window shades and Install interior window covers to block heat coming through the glass.
• Apply heat blocking film on the exterior of the windows. We installed VViViD perforated window vinyl and it lowered the window glass temperature 20 degrees.
• Most 12 volt DC air conditioners lack enough blower pressure to push cool air to the front of the van. Small fans inside will help circulate the cool air a little better. Some roof fans can run with the dome closed to operate like a ceiling fan. Remove one vent as mentioned below.
• A dehumidifier can reduce the humidity and lower the “feels like” temperature.

Roof Vent Fan

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12 volt ACs

Many Class-B manufacturers have switched to installing 12-volt air conditioning units on their Class B motorhomes. When boondocking, a large lithium battery is recommended along with a second engine alternator to power the AC without the need for an onboard generator. These air-conditioners can also be operated while driving to add additional cooling to the van.

Testing – If you are questioning if an AC is working properly, run the AC for 15 minutes and measure the temperature of the air entering at the filter and the temperature of the cold air exiting the vents. If you see a 20+ temperature difference then it is operating within specifications.

Humidity levels, sun load on the outside unit, and several other factors can affect this temperature difference. With increasing temperatures outside, the compressor must work even harder to compress the gas back to a liquid state, drawing more current. Higher ambient external temperatures also decrease the heat transfer capacity of the condenser coil.

Vans are a large metal box and difficult to cool, especially with the miniscule amount of insulation used in the Galleria build. See our tips on cooling.

UPDATE: There have been so many issues with the 12 volt ACs it appears Coachmen is now offering the Truma 120 volt units on new vans.
UPDATE: Sounds like there are problems with Truma AC also. It can’t run on the generator since it draws more power than the generator can output. Update: A “soft-start” module is now available.

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Air-conditioner – ProAir 12 volts

Maintenance:

Clean – the reusable interior filter with plain water. Loosen the 4 screws and remove the cover to access the filter.
Wash – the exterior coils once per year to remove grease and road grime from the fins. Pressure washer is not recommended and could damage the fins.
Fuses – There are several fuses located inside the unit, under the filter. You may want to have some spares just in case.

Problems:

The power cable size is 2 gauge. There were recalls of early installs because coachmen miscalculated the gauge cable required and had to replace with heavier cables.  There have also been numerous issues with bad installations that resulted in water pouring out the filter onto the bed. Some owners are on their third ProAir.
Other issues were bad crimps in cable resulting in a low voltage shutdown when the compressor starts. After numerous problems, coachmen now installs the Turbo Air II.

Modifications:

One of the projects after the purchase of Gal_1.0 was to test other fans to find one that would be quieter with similar air flow specifications. Contact us for more information.

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Air-conditioner – Premier Products Turbo Air II

The Turbo Air II is a 22,000 BTU with a 285 Cu Ft/Min air flow.
NOTE: Some people have questioned the BTU claims of RV air-conditioners based on the formula:
BTU = CFM x ΔT x 1.08
BTU=285x25x1.08
BTU = 7,695 not 22,000 BTU ???

Maintenance:

Clean – the reusable interior filter with plain water. Loosen the 4 screws and remove the cover to access the filter.
Wash – the exterior coils once per year to remove grease and road grime from the fins. With the fins located to the front of the unit, you can expect more bugs will meet their maker with this design. (Designers obviously have never been to Florida during Love Bug season!) Pressure washer is not recommended and could damage the fins.
Fuses – There are several fuses located inside the unit, under the filter. You may want to have some spares just in case.

TIP#238: Remove one front vent – to get better cooling to reach the front of the van remove the front vent on the passenger side. Removing two front vents reduces pressure and is less effective on the Turbo-II.

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Truma Aventa Eco

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Issues: There are a few complaints about the Truma.:
– Cost – The Truma is almost twice as expensive as the Gree, which is a larger AC, has heat-pump and Soft Start.
– Soft start – Truma offers a soft start module that is manufactured by SoftStartUSA but charges $424 installed. SoftStartUSA sells a DIY installed module for $279 (Amazon)
– Remote – The remote does not light up making it impossible to see at night.
– Air Filters – The Truma uses two long skinny filters of each side that are extremely difficult to remove/install.
– Roof leaks – A rigid foam adapter to fit the sprinter roof bends the roof sheet metal causing it to leak.
– Reliability – As described below, our AC stopped cooling while on vacation. Truma tech said this is only the second unit they have seen fail. On the other hand, they have only been selling them for a couple years.
– Repairs – With our Truma failing, we discovered it is very difficult to find anyone to repair them on the road. The main install places are Elkhart IN and Lakeland FL and a mobile techs in Phoenix AZ and Austin TX.

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Inrush Current: There is a momentary spike in current when an air conditioner (AC) compressor first starts. Usually, it is often 2-3 times greater than the ordinary operating current. It is caused by two factors:
Capacitor charging: The majority of AC compressors have a starting capacitor that rapidly stores and releases energy to give the compressor motor an additional kick when starting.
Compressor Inertia: Because a compressor rotor at rest must overcome inertia and create a rotating magnetic field, the compressor motor draws more current than when running.

Inrush current can shorten the life of AC components. If the current is higher than the breaker amperage, the circuit breaker might also trip.

What Is Soft Start – A soft start for an RV AC is a small electronic device that reduces the inrush current during startup. As mentioned, compressors draw a significant amount of current when the compressor starts up. By reducing the inrush current, it prevents issues like tripping the circuit breaker or overloading a generator/inverter. A gradual startup can reduce mechanical wear on the compressor and enhance the longevity of other components. Other devices running in the RV will benefit with the elimination of low voltage drops and voltage spikes when the compressor starts.

A soft start module usually has four wires that connect to the compressor and startup capacitor of the AC unit. The module is mounted inside the AC unit near the compressor and capacitor. Some soft starts also include features like a short-cycle delay timer and overcurrent and stall detection. 

Some RV ACs like the ProAir Gree (China) already have a soft start module installed. New AC designs will use a variable speed compressor that will not even need a soft start. They can vary the speed for the amount of cooling needed.

Soft Start False claims:
– Increase AC cooling capacity – The soft start module does not affect cooling performance or efficiency. It only modifies the very brief startup process and has no effect when the AC is running.
– Eliminates all power-related issues – While it reduces the inrush current, it does nothing for other power-related problems such as voltage fluctuations, spikes, or inadequate generator capacity.
– Saves significant energy costs – Soft start only reduces energy for a brief few seconds during startup and has no effect when the compressor is running.
– AC Runs Quieter – While it may reduce the ‘clunk’ of the rapid compressor startup noise, it will not change the noise level during normal operation.
– Protection the AC from electrical issues – As mentioned, the module does not protect from spikes, low voltage drops, or lightning.

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Truma Aventa Eco Failure – In 2024 we planned a 6-week tour of National Parks and State Capital Buildings. The night before leaving, we turned on the Truma to cool down the van for an early start. The next morning, we found the driver’s side bed soaked, water running down the wall, and the Firefly fly touch panel flooded and inoperative. After drying the bedding and mattress, we left on our trip thinking the problem was due to the nose-down angle of our driveway. 

A few days later, while touring the Dakotas, the AC stopped cooling. The compressor was running but no cool air. We contacted Truma, and they recommended a couple of RV repair shops. The shops said it would be 2-3 weeks to get in, and we’d have to leave the van for 2-3 days. Truma in Elkhart was 3 days each way, so instead, we decided to purchase a portable 1500 BTU AC unit and continue with the trip. The cooling efficiency was poor, so we purchased a Harbor Freight blue tarp and clamps to close off the front cockpit area to reduce the volume needing to be cooled. This was adequate for the few days we needed AC. We followed cool weather across the country to reduce the times we’d need to setup the AC. Arriving in Louisiana we got news a hurricane was heading for our house but that’s another story. Back home, Truma replaced the AC under warranty.

The leak was caused by the rigid foam adapter used under the Truma AC for the sprinter roof ribs. It caused the roof sheet metal to bow inward and water leaked past the seal. For the replacement AC, a second seal layer was installed as well as additional sealant.

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13 – Heating
14 – Cooling
15 – Electrical System

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