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Old 07-03-2006, 12:35 PM   #29
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Just to put another nail in the DH coffin, they use a lot of juice. Maybe somebody said that already, but there you go.

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Old 07-03-2006, 02:25 PM   #30
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I picked this up off villagekitchen.com

Carrier AIR V Recreational Vehicle Rooftop
15000 BTU Air Conditioner in White or Ivory
15000 BTU Air Conditioner with Electric Heat in White or Ivory
15000 BTU Heat Pump with Electric Heat in White or Ivory
Coleman 15000 BTU Air Conditioner and Heat Pump
Duo-Therm 15000 BTU Air Conditioner and Heat Pump


I needed to buy an air conditioner for our trailer for the summer of 2006. I was not really impressed by any of the recreational vehicle air conditioners (RVAC's) by Carrier, Coleman or Duo-Therm. I am sure they are all reliable and operate just fine however...

I was definitely not impressed by the air conditioners manufacturers brochures and advertising. Most seemed to state redundant information or claimed they were best because they had higher cooling capacity and/or indoor blower capacity. Do not accept these claims at face value because they may have been true at some time but may not be true today. Brochures were often confusing as they feature important points out of context. If a specific feature is important to you please double check that your choice has that feature and how well it works. Just because a manufacturer notes they have a three speed fan do not assume that your unit from the same manufacturer will have a three speed fan.

I prefer engineering facts like Energy Star rating and SEER and documented tests. I did not see any RVAC's that was Energy Star rated unit. I did not see any unit mentioning SEER and only a few mentioned the power consumption in watts under the test conditions of Air Conditioning and Refrigeration Institute (A.R.I.).

I get the impression that recreational vehicle air conditioning was considered a poor relative designed to work two weeks a year for twenty years so efficiency was of low importance. The feeling came from my research and the fact that only the Coleman Mach 3 P.S. was designed for improved energy efficiency. They claim the 3 P.S. uses 30% less energy then other 13500 BTU recreational vehicle air conditioners so there is definitely room for improved efficiency in RV air conditioners. Coleman also includes in the Mach3 PS brochure the watt draw at two test scenarios defined by the A.R.I. Standard 210 a definite move to open comparison. The Mach 3 Plus 13500 BTU model 8333 brochure notes the wattage as 1595/1924 so the watts per 1000 btu calculate as 118/143.
Std . conditions of 80ºF DB 67ºF WB indoor 95ºF DB outdoor at 115 volts power draw was 1147 watts = 85 watts per 1000 btu
Max conditions of 95ºF DB 71ºF WB indoor 120ºF DB outdoor at 103 volts power draw was 1355 watts = 100 watts per 1000 btu.

I am looking for a 15000 BTU Air Conditioner (AC) or Heat Pump (HP) rooftop unit offered by the big three - Carrier by TransportAir division of Carrier, Coleman by RV Product division of Airxcel and Duo-Therm by Dometic. From the reviews on the web that I found none of the big three were given any serious negative rating that was not related to features specific for that brand or model. Given the good reputation the big three have and the fact that their units are so similar in engineering design you could easily stop reading right here, however the devil is in the details.

The controls on most of the air conditioners and heat pumps are mechanical, manually set fan and temperature controls. Mechanical controls have been used since the 1950's and are gradually being replaced by electronic controls. If you want heat remember that heat pumps have two shortcomings. First they loose efficiency (i.e. heat output) as the temperature drops. Second the heat pump compressor usually turns off automatically at 40ºF outdoor and turns on a built in electric heater. The electric heater has about 1/3 the heat output of the heat pump when you need heat the most. You should check how and at what temperature the heat pump will send a signal to start your gas furnace.

While researching I looked at the literature on the web by the big three including the service and installation notes. Service and installation notes can be telling as far as the manufacturers consideration of ease of service, installation and costs you might incur later. As an example Carrier and Duo-Therm lists the parts only by manufacturers part number whereas Coleman lists commonly available repair parts by both manufacturers part number and description, like Capacitor Run 7.5MFD 370V, that a service man could use to buy a replacement in any HVAC supply store like Johnstone Supply. The bad part of on-line research is that the brochures, service notes, etc. are usually in PDF format and that they are rarely dated so it is hard to tell what is current from some manufacturers.

Since the 1950's all small air conditioners, both window and RV, have had the same basic layout that generally works well. Carrier, Coleman and Duo-Therm's Rooftop Recreational Vehicle air conditioners are all similarly basic in the construction of their refrigeration, electrical and control systems with occasional exceptions. The next few paragraphs describe basic refrigerant based cooling and heating and the improvements as they occurred since 1950 from the electrical and refrigerant point of view.

I found all three use quiet, efficient rotary compressors that replaced piston compressors in the 1980's. They all use a "run" capacitor for efficiency and a "start" capacitor or solid state thermistor PTC/PTCR to help the compressor start under load. The compressor motor is protected by black plastic overload a little larger then a plastic soda bottle cap firmly attached to the compressor that is sensitive to heat and electrical overload. When the compressor does not start the overload opens in 3 to 5 seconds and automatically resets when it cools in 3 to 5 minutes. If the overload is used too often either it or the compressor burns out.

The compressor first pressurizes the refrigerant gas and feeds this very hot refrigerant gas through a medium sized tube to the outdoor air heat exchanger cooled by a fan which condenses the hot gas to liquid refrigerant at close to outdoor air temperature as the refrigerant flows down the condenser. Next the liquid refrigerant is sent through a small tube at the bottom of the condenser to the capillary tube that meters the refrigerant into the indoor heat exchanger/evaporator at a rate matched to the compressor. The blower wheel moves indoor air over the evaporator which cools and removes moisture from the air while the room heat boils/evaporates the refrigerant. The now room temperature low pressure refrigerant gas exits the evaporator and is fed through a large (sizes are all relative) tube back to the accumulator attached to the compressor. It looks like all the big three all use suction accumulators to catch any liquid refrigerant or oil, that might migrate in cold weather and odd operating conditions, and prevent damaging the compressor which is designed to only handle compressible gas. The accumulator is the black tubular object roughly the size of a cola can attached to one side of the compressor. The accumulator is a very good feature in any air conditioner or refrigeration system and, though not new, they were very rare on small cooling units until the compressor manufacturers started building them into the compressor to stop high failure rates. Older AC units usually will not have an accumulator.

Heat pumps differ from air conditioners in that they reverse the refrigerant flow moving the heat to the inside and the cooling to the outside. A reversing valve mounted close to the compressor and feed the hot gas to the indoor heat exchanger and remove heat from the outdoor air. The capillary tube metering the reverse flow of refrigerant is sometimes replaced by restrictions parallel with bypass valves. Because heat pumps are more complex some, not all, use modern digital control systems with four sensors to measure indoor and outdoor air and heat exchanger temperature. Some may include a restart delay and auxiliary heater controls to start your gas furnace.

A single blower motor usually runs both the indoor air blower wheel and the outdoor air fan. The Carrier low profile air conditioners/heat pumps have separate fan and blower motors. Coleman uses a run capacitor on some models to boost the blower motor efficiency and lower electric consumption. Carrier and Duo-Therm do not use a blower motor run capacitor. Most blower motors are usually two speed although some Duo-Therm and Carrier Ducted rooftop recreational vehicle air conditioning units may have a three speeds. Do not be mislead by high Cubic Feet per Minuite (CFM) blower ratings - quiet operation is much more important. The blower is essientially in the same room as you are so a three or more speed indoor air blower might be the difference between a quiet nights sleep or life in a wind tunnel.

What would I like to see improved? Well first the lack of real data in sales literature about energy consumption efficiency at specific operating conditions as defined by the ARI. Airflow per minute at the various fan speeds is more important to engineers then consumers. Noise, both inside and outside at various fan speeds, is important to consumers so ratings should be included in brochures. I was confused by manufacturers brochures that blend descriptions of similar units. I had to reread the brochure a few times to begin to understand the differences between Carrier AIR V / AIRV heat pumps and Carrier AIR V / AIRV ducted heat pumps.

Next would be an electronic short cycle delay. This and digital controls are something all, this means your home units also, air conditioners and heat pumps should have for reliability and efficiency. I have talked a little already about the compressor overload. Many more things can cause a compressor to short cycle in an recreational vehicle then a home air conditioner. Short cycling occurs when someone adjusts the thermostat, a power failure occurs, generator burps or someone trips and pulls the RV power plug within 3-5 minutes of the compressor turning off. The short cycle delay keeps the compressor from trying to restart before pressure in the refrigerant circuit equalizes. When restarted too soon the compressor draws the Locked Rotor Amps ~60 to 75 amps for a 15k BTU air conditioner until the overload opens, a circuit breaker trips or a fuse blows rather then the 12-14 amps it normally draws. In the few seconds before the overload heats up the motor wiring starts to fry, trailer/RV wiring and plugs will be severely stressed and your lights will dim.

Short cycle delays are available for home units at a reasonable cost and come standard in some electronic thermostats. The lack of a short cycle delay is a very common cause of service calls. The manufacturers agree because they include a short cycle delay as standard equipment on most RV air conditioners and heat pumps that have digital controls. It should be standard on all RV units.

Blower and fan motors should use a "run" capacitor to increase electrical efficiency. The capacitor feeds power to a motor winding at the proper rate and time to boost the motors efficiency and lowers electric consumption by 10 to 20%. The big three use them on compressors so why not the blower motor?

Fan and blower motors with oil cups to keep them running many years longer. A few drops of 20w motor oil every few years can triple the motors life. Some motors have oil cups but most do not.

Efficiency is limited by cost considerations. Larger evaporators, condensers, and more efficient compressors and blower motors used in the Coleman Mach 3 P.S. are proven methods to improve efficiency. I wonder if Coleman put a more efficient compressor and blower into a chassis with 15000 btu condenser and evaporator to create the high efficiency Mach 3 P. S.?

Using some of these features would cut operating costs and increase efficiency at a small price increase. An additional benefit would be increased air conditioner life expectancy. Efficiency and specifications go hand in hand so let's review some of the 15000 BTU RV units

Abbreviations: A=Amps FLA=Full Load Amps LRA=Locked Rotor Amps AC=Air Conditioner HP=Heat Pump W=Watts(VxA=W) BTU=British Thermal Units OZ=Ounces R22=Refrigerant Type 64/65/66=Different specifications from different source documents CFM=Air Volume in Cubic Feet per Minute

Carrier - www.transportaircon.carrier.com www.airv.com
Most units have easily changed air filters. 1 year warranty.
15k BTU AC #68RV15102A: Compressor 64.5/60.3LRA - Unit ~14.5A, 1472W - Fan 325lo/402hiCFM - R22 - 98 watts per 1000btu
15k BTU HP #68RV11112A: Compressor 64.5/60LRA - Unit rated ~12.7A 1482W - Fan 365lo/350hiCFM - R22 - 99 watts per 1000btu
15k BTU AC #68RV14103A 99-- 00468-- 10 : Compressor 59LRA - Unit ~14.1A 1582W - Fan 300cfm - R22 - 105 watts per 1000btu
15k BTU HP : Compressor 59LRA - Unit ~14.1A 1582w - Fan 300cfm - Refrigerant 16.9ozR22 - 105 watts per 1000btu

Dometic Duo-Therm - http://www.dometicusa.com/climate.php?id=ac
3 year parts & 2 year labor warranty.
penguin 15k BTU Compressor=12A 64LRA Fan=3.3A 380cfm - R22 2 AND 3 SPEED fan
briskair 15k BTU Compressor 11.5-12.7/12.9/12.7/12.3A 50-60/60/79/77LRA Fan 2.5/2.0A 380cfm R22 calculated watts 1460 = 97 watts per 1000btu
penguin 15k BTU HP Compressor 12A 64LRA Fan 3.3A 380cfm Refrigerant 21.5ozR22
briskair 15k BTU HP Compressor 12.9/12.5-12.7A 60LRA Fan 2.5A 380cfm R22

Airxcel (airxcel.com) RV Products (rvcomfort.com) Coleman
2 year parts & labor warranty
Mach 15k BTU 8335 14.8AC 71LRA 1748W1 2117W2 FLA16 PTCR 325cfm comp12.6FLA fan2.7/3.4A ARIstd1748max2117 71LRA Tecumseh 17oz - 116 watts per 1000btu / 141 watts per 1000btu
Mach 15k BTU HP2 8535 15HP desiredTemp80º shortCycling FilterRemoveGrill blowerMotorMayHaveOilCups 3minShortCycle comp12.6FLA fan2.7/3.4A ARIstd1748max2117 71LRA 21oz capTube 320cfm2speed compAccum TecumsehRK225AT-026-A4(15500kbtu) 3capsStartRelay 5ºheatDropBelowThermostatStartsHeater - 116 watts per 1000btu

Carrier literature mentions that the 15000 BTU "free flow" air conditioner draws 14 amps when cooling while the 15000 BTU "free flow" heat pump draws 12.7 amps in cool mode. I e-mailed carrier at the airv and transcold web sites about this but got no answer. I checked the repair literature for both units and found they use different compressors, however both compressors use the same overload so the Amp draw must be close. I also saw mentioned in Carrier literature the use of Carlyle compressors. In looking at the Carlyle literature the largest 115 volt EC compressor they list is 14000 BTU (soxxx mentions that their compressors should be used at 7% less then rated BTUS) so are the 15000 BTU Carrier units using a custom made compressor or? Also some advertisements on the web claim the compressor is a Carrier compressor.

Pricing is always a big consideration. I hate to spend more then is necessary and I can't let that research go to waste.

Amazon 15k BTU top and bottom free flow delivered - AC $559 - AC with electric heat $599 - Heat Pump NA

EBay 15k BTU top and bottom free flow delivered - AC $554 - AC with electric heat $593 - Heat Pump $689
List 15k BTU top and bottom free flow - AC $766 - AC with electric heat $810 - Heat Pump $890

Selling price of complete units delivered ranged between 72 to 77% of list.

Last revised June, 2006.
------------------------------------------------------------
FYI to all, I am not aware of who the author of this document is so make sure you do your own research to verify what is in the article above.

Jack








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Old 07-04-2006, 03:26 PM   #31
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Here it is the 4th of July and I'm working and the A/C. The good news is I have made some progress that I believe will be of interest to those with under-performing A/C units, especially in newer trailers. My issues are inability to keep the trailer cool enough in mid-90 degree heat and removal of excess humidity. Here is what what I found. Sorry I did not take any pics. My unit is a Dometic Penguin 11K btu.

Removed the grill to begin the investigation. Then removed the lower bracket that holds the A/C to the roof. Immediately noticed a lot of wires blocking the return air ducts. Re-routed them out of the way. Noticed the thermostat temp probe was right against the chassis. Since the chassis is cool to the touch, I suspect this was resulting in premature shut down of the compressor. Moved the probe. Reading the manual, it was real clear that all openings to the area between the inner and outer skin (within the 14 x 14 area where the A/C is mounted) had to be plugged as this area is part of the return air plenum. AS had not plugged any holes and left large openings in each corner. Basically I was drawing super hot air into the return plenum. Filled all holes and gaps with aluminum tape or caulk. Also noticed the grill did not fit well to the unit. This allowed mixing of hot and cold air. Used stick on weather stripping to solve this problem.

By doing all of these minor things I have increased the temp differentiation (conditioned air compared to intake air) to almost 22 degrees. I suspect that is about as good as I will get but would welcome comments from others.

I still can't figure out the humidity issue. Unit seems to hold condensation for a long time begore it appears in the condensation drain (which is clear). If I turn the A/C off, there is a gush of condensation. It is almost like the airflow is keeping the condensation away from the drain. I have not been on the roof to see if there is anything to look at from that angle.

I'll close on this note. Condensation drain fitting was covered in caulk which I thought odd so I removed it. Naturally the caulk was covering a leak. Take the fitting out, add a little plumbers putty, re-install, no leak . Why couldn't they have done that????

Greg
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Old 07-04-2006, 06:06 PM   #32
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In defense of Humidity:

I have no problem maintaining my cigars when traveling in my 2006 23' s SE (62-70% depending on origin).



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Old 07-04-2006, 07:12 PM   #33
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Thumbs up Good Work Greg

Quote:
Originally Posted by ptrvr
Here it is the 4th of July and I'm working and the A/C. The good news is I have made some progress that I believe will be of interest to those with under-performing A/C units, especially in newer trailers. My issues are inability to keep the trailer cool enough in mid-90 degree heat and removal of excess humidity. Here is what what I found. Sorry I did not take any pics. My unit is a Dometic Penguin 11K btu.

Removed the grill to begin the investigation. Then removed the lower bracket that holds the A/C to the roof. Immediately noticed a lot of wires blocking the return air ducts. Re-routed them out of the way. Noticed the thermostat temp probe was right against the chassis. Since the chassis is cool to the touch, I suspect this was resulting in premature shut down of the compressor. Moved the probe. Reading the manual, it was real clear that all openings to the area between the inner and outer skin (within the 14 x 14 area where the A/C is mounted) had to be plugged as this area is part of the return air plenum. AS had not plugged any holes and left large openings in each corner. Basically I was drawing super hot air into the return plenum. Filled all holes and gaps with aluminum tape or caulk. Also noticed the grill did not fit well to the unit. This allowed mixing of hot and cold air. Used stick on weather stripping to solve this problem.

By doing all of these minor things I have increased the temp differentiation (conditioned air compared to intake air) to almost 22 degrees. I suspect that is about as good as I will get but would welcome comments from others.

I still can't figure out the humidity issue. Unit seems to hold condensation for a long time begore it appears in the condensation drain (which is clear). If I turn the A/C off, there is a gush of condensation. It is almost like the airflow is keeping the condensation away from the drain. I have not been on the roof to see if there is anything to look at from that angle.

I'll close on this note. Condensation drain fitting was covered in caulk which I thought odd so I removed it. Naturally the caulk was covering a leak. Take the fitting out, add a little plumbers putty, re-install, no leak . Why couldn't they have done that????

Greg
A 'delta T split' of 22 deg. is about all that you can get from a modern roof A/C unit. The spec calls for 18-22 deg so you are maxed out. I found the same poor install areas on mine and corrected tham as necessary.

I installed a Carrier Air V 15K heat pump unit last week. It is the super low profile unit. Worked great on a '72 Safari 23' in the mddle of the NM desert in the bright sun. I really like the design of the Carrier and the fact that the internal drip routing channels the condensate to the rear to be picked up by the condenser fan and sprayed over the condenser. Very efficient, IMHO.
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Old 07-04-2006, 08:05 PM   #34
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Lew, that is good to know about the Carrier. I will replace mine with a 13.5 if my little fixes don't net me a COLD AS.

Greg

PS: How's vacation???
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