Roof vs Cruise air

[phorner]

I may be wrong on this, but I don't think so. Removing or replacing the ceiling on a Liberty will probably entail a little more effort than raising and restoring the Titanic.

Not only would the cost be excessive, but I would fear that the value of a bus (and a Liberty in particular) having the CruiseAir's abandoned, holes cut in the roof and roof airs added would drop to about nil.

I would be extremely reluctant as a buyer to consider a bus with such an extreme modification from what the manufacturer/converter had installed. I would question the safety and reliability of a bus that had been substantially "experimented" with.

Although I strive to maintain our bus in the manner that suits our lifestyle best, I always try to look at any proposed "modification" through the eyes of a prospective buyer. I have yet to stray far from the factory-original systems with the exception primarily in the replacement of audio/video components.

In my opinion, keeping the bus as close to "like new" as I can best preserves its value..... well, as best as the value can be preserved keeping the current market in mind!

[jack14r]

I checked today and the condensing motor is a 1625 RPM 48YZ frame 1/4 horse power,the squirrel cage blower fan is 6 5/16 in diameter and 5 1/8 in length.The motor is rated for 3,0 amps and I verified that the condensing unit fan only pulls 1.2 amps.My question is with a 1750 RPM motor how much would the current increase and would there be any real airflow increase?

[Steve Bennett]

We have 3 CruiseAirs in our 40' Marathon. We changed the motor on the blower to a larger, higher RPM unit (I believe it is 1,800 RPM) we also changed the condenser to a double row unit. The other alterations we made were enlarging the exhaust area on the condensing unit (at the bottom) opening up the area on coach floor, adding the late model Marathon rubber ducts under the coach. Removing the foam insulation around the duct area of the floor. These ducts all face to the drivers side, of the coach. All 3 condensing units are behind the front bumper. We also moved some of the wiring,and coolant hoses so they would not interfere with the air flow. The other change was wiring the blower motor to operate 100% of the time, any time the unit & SMX panel are powered up. We also run the fan on the evaporator side constantly when the unit is on. We recently changed the location of the ducting on the front CruiseAir so it would not recirculate the cool air. We moved the intake to below the front overhead cabinetry, making the area behind the TV a large plenum, and ducted it out at the top of the cabinet on the passenger side. We have also insulated all of the ducting in the coach, and have replaced the screens in the output vents to a less restrictive design. We have only had 1 high pressure shut down since making these changes (a 108 degree ambient with a 20+MPH cross wind at a 5,000 foot elevation heading North on 395). I believe the high density altitude, cross wind airflow, and extremely dry air all contributed to the shut down. We are able to keep the coach 70 degrees inside on 100 degree plus days. Keep in mind this is a non-slide 40' coach, we also keep the blinds down in hot weather to help with insulation.

[johnklopp]

Jack,

A bit rough to calculate the changes based on the available data.

I have used standard design conditions for the missing data. Condenser air flow is estimated at 900 CFM at a .75 inch of water column pressure drop across the coil.

Increasing the motor RPM from 1640 RPM to one with an RPM of 1750 will produce marginal results. My calculations show a new air flow of 960 CFM with a new differential pressure across the coil of 0.9 inches and a new HP of 0.2

Best bet may be to slightly increase the diameter of the blower wheel, currently 6 5/16 diameter keeping the existing motor. The discharge scroll around the blower wheel typically has enough room for a small increase in diameter. My calculations show an increase in CFM to 965 using a blower wheel 6.5 inches in diameter. A further increase in diameter to 6.75 inches will result in 1071 CFM using the existing motor. The motor horse power appears OK based on the current power draw of 1.2 amps with a 3 amp rating.

Keep in mind that the actual CFM has not been measured and neither has the pressure drop across the coil. The bottom line is that more CFM is possible without increasing the motor RPM.

My recommendation would be to add an additional fan or blower on the opposite side of the coil to increase air flow if you only want to make modifications on the air side.

If you want to improve the performance as much as possible, change the condenser coil as recommended earlier.

[GDeen]

One thing I learned with my cruiseairs - I set the galley thermostat lower than the front. In my Marathon, they tend to blow the discharge cold air at each other. If they are set to the same temp, the galley will shut down and the front will blow and blow and do a better job of cooling the mid salon/galley area than it does up front. With the Salon unit running and blowing towards the front, it helps quite a bit in keeping the front cool.

Under theory of staying ahead of the heat, I also drop the front shades immediately when stopping to help keep the sun out of the drivers area which tends to be a big greenhouse....My cruiseairs do a fine job of keeping the coach cool even in very hot weather. Staying ahead of the heat curve though is very important - use side shades and awnings if appropriate.

Of course, since we have the OTR air, there is no need to worry about the cruiseairs working while underway...

[Kenneth Brewer]

One thing I learned with my cruiseairs - I set the galley thermostat lower than the front. In my Marathon, they tend to blow the discharge cold air at each other. If they are set to the same temp, the galley will shut down and the front will blow and blow and do a better job of cooling the mid salon/galley area than it does up front. With the Salon unit running and blowing towards the front, it helps quite a bit in keeping the front cool.

Should have thought of that, so simple, and really important with an H3. Duh....

While camped for any length of time beyond an evening and night, the outside sunshades over the windshield and driver/codriver windows are imperative, when dealing with daytime temps over 102 or so, besides the awning and inside shades.

[jack14r]

Thanks John,I thought that the flow would not be significant with the higher RPM,I hope the pictures come through.

[jack14r]

John,I have ordered a blower fan that is 6.75X5.625,I will have to modify the cage inlet a little to get it to work but I have 2 extra that i scrounged out of a scrap pile..I cannot measure CFM but I can measure air velocity and motor current,I will install it in my extra unit and report the findings in a week or so.

[Jon Wehrenberg]

This is unlikely to be easy with the 2 CAs in the center behind the 2nd bay in a Liberty, but it would appear a small amount of sheet metal work and a second blower or fan on the air inlet side would be all it takes to increase the air flow in the simplest manner. I don't know if it would be easy to mount a fan or pair of fans much like the electric ones found on certain cars, but that comes to mind.

[jack14r]

In my coach the distance from a panel or something else would restrict an additional fan in 2 of the 4 cruise airs.If I can increase the airflow with just a fan change this exercise might be worthwhile,if not,I have lost little,anyway I always like these type of projects.