Roof vs Cruise air

[CAPT MOGUL & Sandy]

Dometic does not seem to want to be competitive with the price of cruise airs,just the compressor is over $500,and most roof airs are under $650,a new condenser from AAP is over $2500,but I love the cruise airs as they are very quiet and really cool great.I also think that not cutting holes in the roof is a real plus.I hope that Dometic gets more reasonable on their cruise air units.

Jack, if you don't mind,,,where did you find the roof air under $650? Ed is searching for one now.
Sandy

[jack14r]

John,you are right that the yacht units are water cooled,and the compressors are off the shelf Tecumseh #AKA8515 EXA they are rated at 15,000 BTU.I would like to find a condensing fan motor that was higher RPM and of course would have to be more HP that would fit in the same space,I think that this would help a lot.I don't think that Dometic really wants to improve the cruise air but just keep it as is and keep manufacturing it.

[garyde]

I am always amazed how much action this topic gets. Its crazy. This could go on to infinity. Lets agree that there is more than one way to cool a bus. Everything after that is just degrees. Pardon the pun.

[Jon Wehrenberg]

Actually this is a good discussion because if we pull out the opinions and personal preferences, this discussion has some excellent technical information such as what John has provided. As a result of the information being provided I suspect anyone with a Cruise Air can provide the information to an AC professional and get their CA performing to the max.

One point John makes suggests strongly the importance of maximizing air flow and it makes me wonder if all CA installations in our coaches have unrestricted air flow to and from the condensers.

[truk4u]

Great post John..

Tuga - When the ambient temps got to 90 and the asphalt is cooking, mine would shut down to over temp. Not sure if Liberty made any changes later in the years, but I believe through 2000, you had to remove the fridge to clean the filter. Maybe an XL2 owner will step in.

[JIM CHALOUPKA]

I clean my filter through a removable panel in the pantry next to the refrigerator.

The refrigerator stays in place.

JIM

[johnklopp]

I believe the cruise air is a generally standard design intended of a specific application, but not a bus.

Taking the personal preferences out of the discussion and looking simply at what can be done to increase performance at minimum cost would be a great POG project.

Unfortunately I have never seen a cruise air condensing unit. I assume it is basically a box with the compressor, condenser coil and condenser fan enclosed. The evaporator unit should not need any modifications.

Increasing the air flow would probably be easy by replacing the fan or the motor or both. Two options exist. The first is the motor speed. Based on a 60Hz power supply to the unit, it must operate at 1800 or 3600 RPM. The motor name tag may show a slightly different speed such as 3450 RPM. This is the rotational speed of the motor rotor, not the rotational speed created by the frequency and the number of poles on the motor stator. The difference is slip and all motors have some to a varying degree. To simply increase the speed by a few hundred RPM is not possible with a standard AC motor.

The next option would be to change the pitch on the condenser fan. I am assuming it is a fan and not a blower. This would result in additional airflow, but the possibility of having and excessive air side pressure drop across the condenser exists limiting the total air flow.
The simplest approach may be to add a second fan on the opposite or side of the condenser coil. A second fan will increase the airflow by providing an increase in the available static pressure. I have no idea of the space available. This may facilitate a better discharge point to keep the hot air away from the patio area.

The best option may be to design a new condenser coil with increased heat transfer. The new condenser in conjunction with increased air flow would stop the cruise air units from cutting out on high pressure and increase cooling capacity by reducing the condensing temperature.

Does anyone have pictures of the condensing unit?
Does anyone have an old cruise air condenser to base design changes on?

The goal would be to develop a condenser with fan that would bolt on to existing mounts possibly with extra brackets. The new condenser could be easily installed by a typical AC technician.

In case you’re wondering, I design vapor cycle systems for military vehicles and aircraft.

[gmcbuffalo]

John I have a CA that I have installed a 12v radiator fan just before the air intake for the condenser. If I run this CA with and without the extra fan on, where is the best place to measure the temps to see if this setup really makes a difference?

[jack14r]

John the fan is a squirrel cage blower design with a 1425 RPM 1/4 HP motor.Greg measure the temperature differential at the evaporator and the ambient at the return inside the bus and then turn on the fan and see if the differential increases.I will take pictures of a unit soon.

[johnklopp]

Greg,

This is a great approach to increasing the condenser heat rejection by increasing air flow.

Take a reading on the inlet and exhaust side of the condenser with the new fan off then repeat with it on.
This will give you an idea of the increased heat rejection with the second fan on. You can also measure the amp draw for the compressor. It should be slightly lower.

Take another set of readings the same time as above measuring the inlet and exhaust side of the evaporator.

If you know what the evaporator air flow is you can calculate the cooling capacity taking into account sensible cooling only and ignoring the latent cooling (moisture removal) Q=1.08 x CFM x differential temperature across the evaporator. The air flow should be listed some ware in the CA documents.

You can also measure the heat rejection of the condenser using the formula above. Multiply the condenser result by 1.4 to compensate for the motor heat and the heat of compression added to the refrigerant since the motor is refrigerant cooled. Estimated factor based on anticipated condensing temperatures.

The above information will help evaluate any modifications made.

John