AC description

George

Member

July 31, 2021 at 8:00 am

This is a topic that has been explored a lot over the years and there tends to be some differences of opinion relating to nomenclature. I will respond with my interpretation of what is meant by the various terms.

When I say bus or Prevost OTR I mean a whole bus heat and A/C system that uses a 6 cylinder Carrier compressor with a 1/4 bay condenser located the third bay back on earlier coaches and ahead of the drive axle on X3 coaches. That system has an evaporator located on the opposite side of the coach, same bay.

The Prevost installed OTR has A/C output ratings ranging from the high 80,000 BTU range on older vintage coaches to over 106,000 BTU on later models.

A Prevost coach that does not have OTR will have what is referred to as “driver’s air”, and for A/C beyond that the coach operator will have to depend on converter installed A/C.

That leads into a topic for debate. Some owners, generally those who may have been told by the coach salesman believe their conversion has OTR. Usually the conversion is a Country Coach, but other converters may also supplement the Preovst installed driver’s air with their own engine driven A/C system that has a couple of evaporators installed in the coach, usually midships and aft to add additional cooling. That converter installed system generally uses a truck type A/C compressor with far less cooling potential than the Prevost OTR system.

The systems described above are engine driven. The A/C compressors get their power only when the bus engine is running.

House A/C systems are usually called “roof airs” which are as stated roof mounted units with evaporators and condensers combined into a single unit and commonly used on conventional RVs. They are powered by a 120VAC power circuit, and output is within the 13,000 to 15,000 BTU range. They have pluses and minuses, but generally speaking they operate more efficiently when traveling down the highway than other A/C units that draw condenser air from low, usually above a heat soaked highway.

Split units, almost always Cruisair units have bay or front bumper area mounted condenser units, and remotely located evaporator units which provide the cool air from within the coach interior. Usually one evaporator will be mounted over the entry door area near the ceiling, with one or two mounted midships, and the last evaporator unit located aft in the bedroom. The Cruisairs are generally in the 13,500 BTU range, use 120VAC power and their benefit is quieter operation.

A third A/C option is a bay mounted unit, not unlike a miniature version of a house unit which is ducted. Those units are generally in the 26,000 BTU range and are less common than roof or CA units.

On coaches with only Prevost driver’s air and converter installed roof or CA units only to keep the balance of the coach cool it is necessary to run one or more house air conditioners from inverters or by running the generator even while driving.

If a coach came with R12 systems, a conversion to 134A is possible but that is dependent upon the condition and type of hoses and always requires a complete change of compressor oil. Some changes from R12 to 134 require a new dryer and expansion valve, but some owners have made the conversion without changing them. A switch to 134 from 12 usually is at the expense of about 15% cooling system efficiency.

Art

Member

August 1, 2021 at 9:37 am

We changed our ’88 coach dash air over from R12 to R134A. It required ALL hoses be replaced as the old hoses are not compatible with the 134 refrigerant. We did this back in the early 2000’s and Prevost did the conversion. It works great and if there was any difference in cooling it was not noticeable. The engine compressors don’t last long (a few years) and/or the hoses connected to the compressor would develop leaks. As I recall Prevost charged around $6000 for the conversion.

Ed

Member

August 1, 2021 at 10:27 am

THANK YOU Jon, that explains away all the confusion in my head. Wow to convert from R12 to R134 appears to be expensive and out of reach of most RVer’s. Now when I read on coaches for sale I will understand what they have…

Safe travels

Dave

George

Member

August 1, 2021 at 2:08 pm

The vast majority of conversions do not have OTR. Liberty predominantly provides OTR on its conversions with Marathon and Vantare use OTR on occasion.

The advantage is if you have a heat soaked coach, real Prevost OTR has so much capacity the interior temps are meat locker cold quickly. If a coach does not have OTR, it becomes a numbers game. There is no way a heat soaked coach is going to be cooled as quickly or completely with house A/C units. Their 45,000 (or 60,000 if four units) is just not going to equal the average BTU output of the bus OTR system.

One of the biggest problems with internet advice and information is defining what is acceptable. To me I want my coach interior at or below 70 degrees. If my windows do not have condensation on the outside I am likely too warm. Others may not even consider thinking about turning on the A/C systems until temps rise to 85 inside the coach. Obviously the best A/C system for a coach is defined by the coach purchaser.

Your use of the coach also plays a large role in how you want it equipped. A lot of folks who use their coach as a second home and usually park or store it on an RV resort, do not need or want OTR because they are almost exclusively using it when parked and the 1/2 bay the OTR system occupies may be more important for storage than OTR.

Someone who does not have OTR, but travels a lot and likes things cool is going to be better served with roof airs and running the generator because roof airs are more efficient than CAs when on the road.

Each buyer has to make their own determination about what is best.

Greg

Member

August 1, 2021 at 7:44 pm

If I understand correctly OTR is a big compressor run by the engine and cools ice cubes going down the road. What do you do when parked in a campsite?

Dan

Member

August 1, 2021 at 8:50 pm

Hi Jon, et al.,

Definitely grateful for the cooling performance of our OTR air (especially crossing Westward to Indio)!

Question: I’ve not seen anyone discuss the feasibility of using a standing tower A/C in lieu of Cruisairs or even rooftop A/C’s?

Would a tower A/C (capable of cooling 400 square feet) be an option when plugged into 50 Amp shore power – perhaps putting the condensation hose down the shower drain?

Not sure whether the unit would need to be vented to draw from outside or, if there is sufficient space within the Coach to essentially recirculate the now cooler air?

Obviously no HVAC expert, but asking as we’re already getting pressure shutdowns of the mid-Starboard Cruisair unit (only one we’ve been running at 76 degrees…just to offset the 107+ degree temps) – even after hosing the entire pad under the Coach several times today.

Be grateful for any feedback, thoughts/recommendations.

FYI – we have emptied and shut off the refrigerator, wine frig and microwave at the central Control Panel switches. And, are doing everything else we can think of the minimize power draws and help cool the Coach (5-coats of rooftop insulating paint, shades closed and awnings out, etc.).

Yes, we know the best solution is to not be in Indio this time of year – but, that wasn’t an option this year.

Bill

Member

August 1, 2021 at 9:14 pm

We have not been anywhere yet where the Country Coach version of OTA didn’t keep the whole coach nice and comfortable. We just got back from 3400 miles to FMCA in Gillette, WY and a bunch of other places that were well over 100 degrees. Unless the SE humidity would throw it for a loop I can’t imagine wanting anything else. Simple, reliable, controllable and doesn’t take a ton of engine power. I can’t even feel it when the compressor comes on.

Jerry

Jim/Chris

Member

August 2, 2021 at 8:25 am

If a coach has OTR when it is parked at a campsite the house A/C units are used.

We can all get into a pissing contest about the efficiency of various systems, but it is a waste of time because we all have different tolerances for heat. The buyer of a coach has to decide what is tolerable.

There is no way in the world a converter installed system they call OTR is equal to the Prevost OTR which is designed to keep 50 bodies in a coach driving through Arizona in August cool. Some people do not need to be as cool as others so in some cases the small converter installed system is adequate. In my case I would be suffering unless I could have water running down the outside of the windows.

Art

Member

August 2, 2021 at 9:31 am

Greg and Deb,

If you are asking about the stand-alone A/C units like you see at Home Depot, YES! they work great in a bus. I had to use one when I only had 2 working cruise-air units. It does have to be vented with a large 6″ hose for the hot exhaust and there is a good deal of water to drain away as well. We needed the front cruise air PLUS the A/C unit to keep the front cool while in 100+ in Vegas.

We put it up front by the drivers seat with the exhaust going out the vertical slider window. It comes with an adapter designed for a window to be closed on it and hold it in place. We have also adapted it to connect to a roof vent in the bath area to cool the bedroom when that Cruise-air failed. Others have installed after-market roof airs and I believe this to be the best long term solution to getting a coach cooled off if all 3 (or 4) Cruiseairs are not working. They are cheap, easy to deal with and can be replaced every 10 years or so without a lot of work or expense. Having the option to use the air dump (not vented air only) will cool the coach down in a hurry, even from a very hot start up.

Dorel

Member

August 2, 2021 at 1:11 pm

Thank you, Bill!!!

Chuck & Katrina

Member

August 30, 2021 at 10:38 am

Currently having an issue with the Starboard Cruisair (mid-Coach). Although not receiving any Error Codes, the unit is not cooling – just blowing lukewarm air? It does not sound like the condenser fan is operating…however, I do not have anything from Liberty that would tell me whether there is a fuse, circuit breaker, etc. specific the the Starboard Cruisair condenser fan?

All Cruisair units had just been serviced and R22 @ a month ago…back in Nashville, TN area.

What is curious is that when trying to increase the fan speed on the SMX II control panel…the 5 speed indicator lights all work, but the fan only stays at the original 1st speed level?

I tried to restore the programmed factory settings (by simultaneously pressing OFF, SET & FAN; then pressing SET)…but, it had no impact on the condenser fan.

Have been using a misting set-up to keep the concrete pad cool. This had been working so well for @3-weeks, that we had been able to cool the entire Coach using just the Starboard Cruisair set at 77 degrees…until a few nights ago when it appears the condenser fan stopped.

Does anyone have any suggestions/advice? Is there a circuit breaker specific to the starboard Cruisair condenser fan?

Or, a Cruisair knowledgeable shop/mobile tech in the Indio, CA area – anyone would recommend?
(Vaguely remember reading a previous forum comment about there being a Liberty mobile tech at Motorcoach Country Club during season?)

Fortunately, we are able to sleep in our Villa home vs. on the Coach. And, running the Port and Aft Cruisair units is keeping the Coach plenty cool. Just concerned that if we were to lose operation of one or both of these units, too – not sure where to take them to be serviced? (It’s our first time in Indio.)

2000 Featherlite H3-45

2024 Jeep Grand Cherokee

Leesburg, FL

joel

Member

August 30, 2021 at 7:43 pm

I think there’s thread creep here.
Given the problem you described, I’d call the Nashville area shop that recently serviced your Cruise-Airs and/or the fine folks at:

AAP
Fred Pickering
16388 Industrial Drive
Milford VA
(804) 633-9454

Fred and his crew are the Cruise-Air experts. They should be able to help you diagnose and your problem.

1999 XLV X-6872, liberty #440