Upgrade from Norcold to Dometic CR-1110 E/F-S (compressor fridge)

[funpilot]

In my research on getting the factory to install the Dometic CR-1110, I came across this brief overview. What I did not know is that the leveling requirements are much more forgiving on the compressor version!
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What's the difference between AC/DC Compressor Style and Propane Refrigerators

Propane Style. The propane style refrigerator (more accurately called an ammonia absorption refrigerator) uses heat to operate. This means it can operate on a propane flame, but also means that when being operated on 120 volt AC or 12 volt DC, these power sources also have to generate heat. On 120 volt this is only a 1 to 3 amp draw, depending on the size of the refrigerator. On the 12 volt side, however, the amperage draw jumps to between 8 to 23 amps. The refrigerator should be run on 12 volt only when the vehicle is running and charging the battery.

An ammonia absorption refrigerator has to be level any time it is in operation and stationary. It also requires a fairly sophisticated ventilation system to expel heat from the cooling unit. If either of these two conditions are not met, the cooling unit may become permanently damaged.

AC/DC Compressor Style. The AC/DC compressor refrigerator can be run up to 30º out of level and requires only minimal ventilation. Operating on 120 volt, it will pull between 0.4 and 0.975 amps, depending on the size of the refrigerator. The 12 volt amp range is between 3.5 and 6.0 amps. This style refrigerator, which uses a motor, can only be operated on electricity, not propane.

Then Why? Why do probably more than 95% of RVs come with the propane style refrigerator, when they are so inefficient on 12 volt and so temperamental? The answer is: propane. With standard propane tanks, an RV with a propane refrigerator can go for weeks without the benefit of any hook ups. The AC/DC compressor style, although much more efficient on 12 volt than the propane style, will barely last 24 hours with a standard battery, without recharging the battery. To be truly independent of outside power the RV would have to have a lot of batteries or some means to constantly charge (in a significant way) a few batteries.

There is a definite need, however, for the AC/DC compressor style. Any situation where the proper ventilation requirements for a propane refrigerator can't be implemented (such as many boats) is a perfect candidate. If 12 volt is going to be the only or main power source, then the AC/DC compressor style is the only way to go. If it is known that propane will never be considered as a power source, then there is no reason to put up with the requirements of a propane refrigerator.

[Bill]

I agree that a compressor unit is a wonderful thing. We have one that we use as a chest freezer (not a refrig) as we cross the country, and we love it. Completely dependable, low power drain, and it maintains below zero temps even on very hot days.

However, the argument about levelling an absorption refrig is a bit overblown. While precise levelling was needed in the "bad old days", absorption refrig units are nowhere near as level-sensitve as they used to be. For example, the manual for the Norcold unit that is standard in the TM says

"The refrigerator is made to operate within 3 degrees off level side-to-side, and 6 degrees off level-front to-back, as looking at the front of the refrigerator."

Since the refrigerator is mounted sideways in a TM, side-to-side in the refrig translates to front-to-back of the TM, and vice versa. If the TM is 3 degrees off level front-to-back, that means that the TM is nose-high (or nose-low) by almost a foot. Similarly, if the TM is 6 degrees off level side-to-side, that means 9 inches wheel height difference. Although I am not a levelling fanatic, I never get anywhere near this tilted.

There are many reasons to get (and love) a compressor refrig, and you have hit them well. But sensitivity to level operation doesn't seem to be one of them.

Just my thought. Someone check my math ...

Bill

[funpilot]

Guess I am showing my "camping age" as it has been a while for me .... compared to the world today though, I really think back then were the "good ol days!"

[rickst29]

On my most recent trip - Whitney Portal and Twin Lakes (on the Nevada side of the Sierra), setting the "thermostat" dial control to 5-1/2 worked fine: No freezes in the Fridge compartment, no melted ice cream above.

I did make a slight modification to prevent the latter issue, which is reportedly a common problem when ambient temps are below 90f : I made a small sheet of double-foiled, bubble-wrap insulation to insulate the bottom of the Freezer from the Fridge section. (Simply bought a larger piece at Home Depot, and cut it down to size with a scissors, stuck it on fridge side with some bits of leftover VH-B tape). Without such insulation, the freezer is only "insulated" by the tiny thickness of hard plastic compartment housing, and it tends to get too warm in moderate temperatures. (In really hot weather, 95+, this mod would be unnecessary. But The condenser doesn't run as much in cool weather, and its analog controller is in the Fridge section.)

Because the analog "tube" thermostat again worked pretty well, AND because I'd need to avoid hitting wires and gas pipes with my drill, AND because the installation would need to reach control wires which are concealed under insulation: I hope to completely avoid the installation of a digital controller and thermocouple.

[Padgett]

Sounds like the best thing would be a compressor fridge in the TV and propane in the TM. I keep cold stuff cold when travelling in a 44qt 12v peltier cooler.

Mine has no problem with 12v on the fridge since it seems to be missing but propane works well.

[rickst29]

Originally Posted by funpilot

Propane Style. The propane style refrigerator (more accurately called an ammonia absorption refrigerator) uses heat to operate. This means it can operate on a propane flame, but also means that when being operated on 120 volt AC or 12 volt DC, these power sources also have to generate heat. On 120 volt this is only a 1 to 3 amp draw, depending on the size of the refrigerator. On the 12 volt side, however, the amperage draw jumps to between 8 to 23 amps. The refrigerator should be run on 12 volt only when the vehicle is running and charging the battery.

Correct figures for Norcold N300.3: 120VAC = 1A and "12VDC" = 11-12A.
and Dometic CR-1110: 120VAC = .8A and "12VDC" = 7.2A @95F, with a small variance on temperature.

Important correction: An unmodified "Tow Vehicle" will not protect TM batteries from Discharge until those batteries have fallen to about 50% SOC. Details: http://www.trailmanorowners.com/foru...ad.php?t=16995

And the best reason for buying a Dometic "CR" Fridge: They actually work well in temps above 90-95F. The ammonia Fridge design can't do that.

And a nitpick: AFAIK, all TM owners of the Dometic CR-1110 have Solar Power, and a few have other "battery charging devices" too.

[davlin]

Originally Posted by rickst29

Correct figures for Norcold N300.3: 120VAC = 1A and "12VDC" = 12A.
and Dometic CR-1110: 120VAC = .8A and "12VDC" = 7.2A.

Important correction: An unmodified "Tow Vehicle" will not protect TM batteries from Discharge until those batteries have fallen to about 50% SOC. Details: http://www.trailmanorowners.com/foru...ad.php?t=16995

And the best reason for buying a Dometic "CR" Fridge: They actually work well in temps above 90-95F. The ammonia Fridge design can't do that.

And a nitpick: AFAIK, all TM owners of the Dometic CR-1110 have Solar Power, and a few have other "battery charging devices" too.

Don't want to start throwing volts, amps, watts, flux capacitors or dilithium crystals around, but here's some empirical data from our experience with the Dometic.

We find we have no problem with the TM battery being fully charged after a full day (10 plus hours) on the road. Our TM battery is a WalMart deep cycle marine battery (just one), and probably about 18 months old. Nothing special. No solar. No dilithium. I should probably modify this statement to say that we had extreme problems with TM battery drainage and fridge performance initially, until we discovered that Ford does NOT install the fuse and relay for the 12vdc charging circuit. You have to do that yourself. Even if you have the factory tow package. Once we plugged those in, life has been good.

We are not boon-dockers, so we camp where there is electricity. But since we are selling our TM we've had one potential buyer ask "How long will that fridge run on just the battery?" That got me curious, so I ran a very simple test. I turned the fridge on, and attached a voltmeter to the battery. I measured the voltage drop and fridge temp periodically. The science was primitive; I just wanted to see if I could answer the question the next time it was asked. Over the next 48 hours, the voltage dropped .9 vdc while the fridge temp held (basically) rock steady at 39 degrees. The ending voltage was 12.5 vdc. Remember, this is with a Wally World battery, not dual turbocharged racing 6 volt golf cart batteries. No solar panels. The ambient temps were very mild (highs in the mid-70's) and I did not have any other DC drains in play (other than the typical ghosts), so this wasn't a very vigorous test, but it answered, at least for me, the question "Can I stop for a couple of hours with the TV turned off without worrying about the fridge?"

[tentcamper]

Originally Posted by davlin

Don't want to start throwing volts, amps, watts, flux capacitors or dilithium crystals around, but here's some empirical data from our experience with the Dometic.

We find we have no problem with the TM battery being fully charged after a full day (10 plus hours) on the road. Our TM battery is a WalMart deep cycle marine battery (just one), and probably about 18 months old. Nothing special. No solar. No dilithium. I should probably modify this statement to say that we had extreme problems with TM battery drainage and fridge performance initially, until we discovered that Ford does NOT install the fuse and relay for the 12vdc charging circuit. You have to do that yourself. Even if you have the factory tow package. Once we plugged those in, life has been good.

We are not boon-dockers, so we camp where there is electricity. But since we are selling our TM we've had one potential buyer ask "How long will that fridge run on just the battery?" That got me curious, so I ran a very simple test. I turned the fridge on, and attached a voltmeter to the battery. I measured the voltage drop and fridge temp periodically. The science was primitive; I just wanted to see if I could answer the question the next time it was asked. Over the next 48 hours, the voltage dropped .9 vdc while the fridge temp held (basically) rock steady at 39 degrees. The ending voltage was 12.5 vdc. Remember, this is with a Wally World battery, not dual turbocharged racing 6 volt golf cart batteries. No solar panels. The ambient temps were very mild (highs in the mid-70's) and I did not have any other DC drains in play (other than the typical ghosts), so this wasn't a very vigorous test, but it answered, at least for me, the question "Can I stop for a couple of hours with the TV turned off without worrying about the fridge?"

We have the same experience, near fully charger after 6-8 hours if we are not running the fridge on 12v.

[rickst29]

Originally Posted by davlin

We are not boon-dockers, so we camp where there is electricity.... Over the next 48 hours, the voltage dropped .9 vdc while the fridge temp held (basically) rock steady at 39 degrees. The ending voltage was 12.5 vdc....

Nitpick: Unless the first Battery reading showed "surface charge" from a recently disconnected charge cycle, the numbers aren't quite right: Discharge from a ~95% SLA battery without "surface charge" begins at 12.8 Volts. You either burned through only .4 Volts (more likely), or your Voltmeter is really bad (less likely.)

Originally Posted by davlin

It answered, at least for me, the question "Can I stop for a couple of hours with the TV turned off without worrying about the fridge?"

Definitely. But, when the weather is much hotter, the duty cycle of the Fridge might reach 80% (of wall-clock time). Since the TV batteries will take over this load when TM batteries reach about 50% ... that's our worst possible starting point. 10A per hour at 80% duty cycle is roughly the same, for the battery, as 8A continous. 2 hours would consume about 16 AH. For those of us using a pair of wally-world group 24 batteries (Capacity ~70 AH), that takes out another 11%. Not terrible for a short period, and you will be fully recharged after plugging in at camp.

But: I will SWAG that merely connecting directly between the Bargman endpoint wire nut (i.e., and the Fridge 12V input (with a breaker) improves the TV-based Voltage, available at the Fridge terminal under load, by about 0.25 Volts. In terms of SOC, that's significantly better "TM Battery Protection": When you turn off the TV, your TM batteries start downwards from about 65% SOC, rather than 50%. This is a very easy mod, and probably worth doing- if you've got a Norcold Fridge running down the road on 12V.

(Although I don't have one anymore )

[scrubjaysnest]

When I tested the new solar system, the load I used was the fridg on DC at the highest setting. Amps drawn at the start were 11.6 and by the end of the load testing was down to 11.1 amps. I would run the fridg until the Trimetric showed ~a 10% drop in SOC. The fridg was then turned off and the batteries rested two hours. This was continued until battery voltage was ~12.4 which according to Exide is 50% SOC. The Trimetric showed 60 %, the Trimetric bases it's % on Ah used and Ah capacity of the batteries. This all took about 6 hours of run time on the fridg. This current draw also represents about 11 % of the battery bank capacity.
Bottom line a single battery in the TM will be dead in about 4 hours of continuous running without some charging source.