in good shape - brunnhilde part 13

Yesterday I set out to do a bit more testing of powering the Kerstner AC with the Honda EU2000i generator. I have only use the Kerstner once while camping so my experience with it is quite limited. I wanted to have a better impression of it before making the decision to throw out the water and the baby.


for any roof top AC the I replace the Kerstner it must be installed to retain the functionality of the factory vents

outside temperature - with significant solar gain on the roof

inside temperature with the Kerstner AC running; actually it got doen to 64F

the Honda EU2000i has an Eco throttle setting

I wanted to do a number of on/off test with the Honda. By switch the AC from dead off, it imposes the worst surge current. Each time the AC was able to start after a few seconds of grunting, with the Honda in Eco mode spooling up in response to the voltage sag. It should be noted that my test is conducted at near sea level. At higher elevation like in Denver, CO, the generator output will deteriorate quite significantly so it is very possible the AC would not be happy. However I think the main problem with starting in Eco mode has more to do with how quickly the Honda can spool up the engine RPM and the reduction of maximum engine output power has less to do with it - within reason until it hit the ceiling. My estimate of the Kerstner AC is probably BTU is probably no more than 9000 given it's many stages of power loss due to the inherent DC and belt driven design.

Kertsner's Problems:

• DC motor driving a automotive type compressor through a short belt
• two DC blower motors
• two ganged AC to DC switch mode power supplies (with no better than ~85% efficiency) with one external cooling fan (I don't know if the power supplies themselves also have internal cooling fan)

Since the Honda can power the Kertsner a similar sized (BTU) RV roof top AC should consume much less steady state full load current for the Honda. The key question is how well will the compressor and blower motors copes with the momentary sag of the voltage during initial switch on with the generator set to Eco mode.

I conducted more research on all the available RV roof top air conditioners. I have never own an US RV so I learnt something in the process. All US RV roof top AC are design for use with an industry standard of 14" x 14" cutout. This is by no accident and I have to give them the credit for Yankee ingenuity. The common roof vents are also 14" x 14". All these ACs are design to circulate force air through the evaporator by arranging the forced cold air as well as the return air through this opening. I measured the roof cut out of the existing Kerstner and it is about 23" wide by 15" deep. There is little chance one cannot make any of the US RV AC fit, though you have to install all of them backwards, as well as prepare to patch up the larger opening with some sheet aluminum. You may also need to fabricate a plenum of sort.

I made a  bit more progress in my research for a low profile AC. Evidently Carrier made one with only 8" tall. It also has the nicest clean appearance. Alas Carrier no longer make RV AC since about 10 years ago.

I know with appliances when a company stop marketing a line, it is likely sold, or re-branded as another brand. Doing a bit of research, I cannot help but to notice the remarkable resemblance of the Coleman Mach 8 Polar Cub to the low profile Carrier. This can be seen in comparing the layout topologies of the two.

note the marked similarity to the carrier in the layout topology; this one has an optional condensate pump; it also feature a rotary compressor lay on the side at the same location

i do like the clean appearance over the highly embellished styling of the Penguin II

a large internal photo of the mach 8 i could find on the web

At the Coleman site there is confusion as to the smallest BTU size for the Mach 8 series. You have to use the product selector to find it.

Here are the marketing specs:

9,200 BTU.

LOW PROFILE AT 8.25" TALL.

HIGHEST AIR FLOW ON HIGH SPEED.

BACKWARD COMPATIBLE WITH ANY COLEMAN MACH AIR CONDITIONER, AND INSTALLS EASILY FROM THE ROOF FOR DUCTED TOP DOWN MOUNTED SYSTEMS

OPERATES EVEN AT DESERT CONDITIONS OF 120° F

HAS THE LARGEST BTU RESISTANCE HEATER OF ANY RV AIR CONDITIONER

FEATURES A MOLDED ONE PIECE FIBERGLASS BASE PAN

EXTERIOR SHROUD DIMENSIONS: 41.1" LENGTH, 28.4" WIDTH, 8.25" HEIGHT.

INTERIOR SHROUD DIMENSIONS: 20.1" LENGTH, 19.9" WIDTH, 2.2" DEPTH.

MADE IN USA.

NOTE: REQUIRES A CEILING ASSEMBLY IF SWITCHING BRANDS OR FIRST TIME INSTALLATIONS (SOLD SEPARATELY)

IMPORTANT SHIPPING INFO: IF YOU NEED A LIFT GATE (HELP GETTING PRODUCT OFF THE TRUCK), PLEASE CONTACT US AT 1-866-332-7881 BEFORE PLACING ORDER. THIS PRODUCT SHIPS BY GROUND ONLY.

MACH 8 CUB RV ROOFTOP AIR CONDITIONER, 9,200 BTU, WHITE

COOLING/HEATING CAPACITY: 9,200 BTU.

ELECTRIC HEAT STRIP CAPACITY (SOLD SEPARATELY): 6,000 BTU.

ELECTRICAL RATING: 115 VAC, 60 HZ, 1 PHASE.

COOLING AMP'S:

COMPRESSOR: 8.9.

INDOOR MOTOR HIGH/LOW: 1.2 / 0.7.

OUTDOOR MOTOR: 1.6.

RUNNING WATTS @ A.R.I. STANDARD: 1270.

RUNNING WATTS @ DESERT CONDITION: 1550.

RUNNING WATTS-ELECTRIC HEAT STRIP: 1748.

COMPRESSOR LOCKED ROTOR AMPS: 58.4.

METERING DEVICE: BI-FLOW RESTRICTOR.

REFRIGERANT CHARGE - R-410A: 14.75 OZ.

EVAPORATOR AIR DELIVERY (CFM): 300 - HIGH SPEED

This 9200 BTU unit is the smallest RV AC out there. It has a total 11.7A max loaded current comparing to the Penguin II's 14A max loaded current. Of course this does not tell you how it would behave with any modest sized inverter type generator like the Honda EU2000i or the similar one from Yahama.

Comparing the Coleman Mach 8 9200BTU to the Domestic Penguin II 11,000BTU there are some trade offs between the two. The Coleman has lower height design necessitated two blower motors while the Penguin II requires only one. The Coleman is reported to be louder on the outside due to the vertical blowing fan for the condenser. Hence also tends to be less efficient. The Penguin II use of one blower motor would tend to have less audio beating from motors spinning at different speeds. The lower BTU rating gives the edge to the Coleman for installing onto Brunnhilde small interior volume, as well as more headroom for the Honda's 1600W rated and 2000W max capacity.

Searching the web to look for other people's report of using the Honda EU2000i successfully with the air conditioners is not easy as there is a lot of confusion which AC models were used. Also few posters were clear on the elevation, if Eco mode was used.

this guy says he use his 9200  BTU with the Honda without problem, but didn't mention the Eco mode.

more forum discussion of the 9200 BTU with the Honda. Note that these posts were back in 2000 and so it is likely the Honda 2000i was a bit different then. I think these were the older Polar Cub that are taller.

Right now I am leaning towards the Coleman Mach 8 9200 BTU model over the Dometic Penguin II 11,000 BTU model.

here is the youtube video on the ultra low profile mach 8 which is available in 9200 btu


the video do give you a better feel of what the unit construction and design

this installation video really helps me to know what to expect in improvising the mounting to use the Westfalia air distribution vents; note the plastic sleeve he mention must be the cold air out let as it is under pressure from the blower, otherwise it will collapse if is in the suction return path




I do like the way the Coleman Mach 8 design use of a steel frame that is a part of the interior ADB (air distribution box) to pull down the unit and compresss the sealing foam gasket. This serves as the main anchor of the (reverse front of) the unit.

If you watch carefully at the installation video at 3:24, he attachs the soft air collar to one of the two ports. It is the smaller port, so that would be closer to James Cook's cold air outlet vents. I also noted the intended 14" x 14" opening required by this AC, and it should not cause problem with the Heki bathroom vent that is very close to the back of the Kerstner.

Also note at 3:36 when he plug the cable harness into the thermostat side of the ceiling ADB. That thermostat would needed to be reused together with the rotary switch on the opposite side, to replace the control panel for the Kerstner. More check needed on these.

At this point, I feel quite confident I can make the installation work as well as preserving the interior's integrity. It should be significantly quieter than the Kerstner especially running at the low blower speed. My biggest motivation of the hugely improved reliability and simplicity. The question is do I want to tackle another major project.