No fishing this trip. The sole purpose was testing out the trailer. Later this summer I’m spending a week in the Boundary Waters Canoe Area Wilderness. It will hopefully be a great week of backcountry fishing. I’ll miss the comforts of my Tradewind.
Regarding my refrigerator (warning… lots of diagnostic info to follow), the door gasket has been remolded via a heat gun and seals much better. Having now spent some time monitoring refrigerator temperatures and noting the impact of opening doors, I’m seriously considering using one to two top loaded DC units in the Overlander. It’s pretty remarkable how much warm air replaces cooled air each time the door opens. Based on specs alone, the ICECO VL74 or Isotherm BI-172 look interesting.
Regarding my Isotherm Cruise 200 not cooling as expected, I believe I’ve honed in on the issue using a multimeter, a 12VDC power supply, and noting the LED error code display in the controller. Many DC refrigerators use this same Danfoss/SECOP compressor (BD 35 or in my case the BD50). They are highly regarded as reliable and efficient. As a result there is a lot of information online to diagnose problems which has been summarized for future reference below. I'm optimistic I'll work out the bugs in mine and see years of good service.
To recap my specific issue, I noted on our shakedown trip that the refrigerator temps bounced between 43F and 50F (not food safe) and the freezer was right at 32F (dangerously soft ice cream— haha). These temperatures are much higher than when I tested the refrigerator in my driveway a few months ago, in albeit cooler conditions. A handy trick I learned while research refrigerator performance was to use a wireless weather station for homes in the trailer to not only monitor inside and outside ambient air temperatures but also place a second and third sensor in the freezer/refrigerator compartments. This permits remote temp monitoring of these areas without needing to open the doors (which allows hot air to enter the compartments and disrupts monitoring/assessment).
In fairness to my unit, the ambient exterior temps were in the 90Fs (76F inside the airstream) but these Danfoss units are reported to do fairly well even in these conditions (with fridge temps right at or just below 40F even in really warm weather). I also noted the area just under the door gaskets on the divider wall between the refrigerator and freezer was hot to touch (not burn you hot, but unexpectedly warm). This is suggestive of a condenser fan being faulty and therefore heat is not removed from the system. When this happens the working fluid (R134A) reaches the maximal amount of heat it can absorb from the food areas and cooling slows/stops. I’m assuming the evaporator plate is positioned between the freezer and refrigerator compartments in this divider wall, which is why it was hot in this specific location? (not sure about this... still learning)
Upon returning home, when I removed my refrigerator from the cabinet, I noted the compressor was running but the fan that blows air across the condenser (think of this like a car radiator) was not running. In essence, the ability of the unit to further remove heat was compromised. This explained why it would cool to the mid 40’s but no further. Interestingly, I attempted to install a larger fan (these use a typical 120mm computer fan) to verify it would resolve the issue. It worked for a bit but then the compressor wouldn’t spool up… plan foiled.
The newer Danfoss compressor units have a control board (aka controller, which is the brains/circuitry of the unit) with a built in LED to signal error codes if problems are present. Normally the LED doesn’t illuminate. After installing the new fan (and once the compressor stopped) this indicator LED would flash twice, pause, and flash twice again. I consulted the error code reference table in the manual and found out if the control board senses an electrical short in the fan (by monitoring for amp draws higher than expected) it prevents the compressor from starting as a built in safety guard from the system overheating.
In my case the test fan (rated at 0.35A rather than the 0.24A of the OEM fan) was oddly tripping this fault. After removing the fan ground, the compressor started working again. I spoke with a Master Repair Technician and they are surprised that such a slight increase in fan size would cause this since the threshold is supposedly 1 amp. So I might not be on the right track… we’ll see. I have a fan on order (SilenX IPX 76-14, $25, 120mm size, 72CFM, 1200 RPM, 0.22A, 14DBa) that matches the reported parameters of the OEM fan ($60). Hopefully that resolves my issue. If not, my controller may be bad (~$140). My other perplexing issue is that my voltage is dropping from 13 volts to 12 volts (more than expected) when the compressor turns on. I plan to bird dog the connections powering the unit and test it on AC only (which sends 24 volts to the controller, rather than
12V from my DC side).
In the interim (waiting for my replacement fan with a lower amp draw to arrive), I’ve tested the unit by simply placing a box fan behind the refrigerator with the unit removed from the cabinet and left inside the airstream. The unit cooled to 9F in the freezer and 37F fridge on thermostat setting 5 of 7 (with ambient temps kept in the 80Fs using the airstream’s AC unit).
I was honestly surprised how warm the compressor gets and the amount of heat generated during the units operation. Though, it makes sense given that’s how a fridge works… rapidly compressing the working fluid (in this case R134A) that circulate throughout the the unit and serves to absorb heat from inside the unit and transport heat out of the refrigerator via the condenser coils/fins which the fan blows across. As a result, I plan to add a small fan inside the fridge when in use to help move air around the food (promoting heat extraction). I’m also going to add a fan behind my refrigerator to help exhaust the heat produced by the unit out of the roof vent. I plan to wire these both on a switch near the fridge and turn them on when we are using the trailer, especially in warm weather. Hopefully these will optimize the functioning of my refrigerator and ensure its longevity.
For those with Danfoss/SECOP compressor based refrigerators here is a step by step process to evaluate dysfunctional units (note only do this if you are qualified, be careful, consider this for educational purposes only):
Step 1: Check your door seals, air flow around the refrigerator, try adding a fan inside, and limit the number of times you open the doors. Use an ice chest/cooler to store items that will be frequently access (drinks, etc). Listen if the compressor is turning on followed shortly by the fan.
Step 2: If you are concerned the fan/compressor are not running, remove the unit from the cabinet and feel the compressor for vibration and ensure the fan blades are spinning when the compressor is running. If not, bypass the thermostat by installing a jumper wire (a short section of wire with female blade connectors) across the T and C terminals on the controller. If the compressor and fan now runs it’s likely a bad thermostat.
Step 3: If the compressor still doesn’t run with the T/C jumper wire in place, check out the LED light in the controller (unscrew the single screw on the front of the controller and gently pull the box away from the compressor). If the LED is blinking twice, pausing, and blinking twice again disconnect the fan’s ground wire and the compressor will likely turn on. Remove the fan’s ground wire regardless of the LED indicator to ensure this isn't the problem. You can confirm the integrity of the fan by connecting it directly to a
12 volt power supply. Replace if needed.
Step 4: If the T/C jumper wire and removing the fan ground doesn’t get the compressor to run, check the electrical supply
- Turn off the AC breaker and remove the DC fuse supply power to the unit
- Unplug one of the thermostat leads at the controller
- Use a multimeter to read the DC voltage at the battery terminal
- Relocate the multimeter to the +/- terminals on the controller (leave it connected to allow continuous monitoring)
- Turn on the AC breaker or insert the DC fuse
- Compare the voltage measured at the controller to the battery terminal
- Reconnect the thermostat lead to the controller and monitor the voltage continuously before, during and after the compressor starts or attempts to start
Step 5 Interpret the above results
- If the supply is free of loose, bad, or high resistance connections the voltage before/during/after the compressor starts should remain stable (less than 0.5 volt drop and remain above 12 volts)
- If the voltage drops below 10.5 volts the controller will stop the compressor and it should produce a one flash fault code
- If the compressor starts but the voltage slowly drops below 10.5 volts the controller will cut the compressor off as well, so keep an eye on the voltage for a while
Step 6 Resolving connection issues
- Check for faulty breakers or fuses, loose or corroded screw connections, poorly made/corroded crimp connections, damaged wire, etc
- Consider connecting the fridge to a compatible (12 or 24 volt) and fully charged battery (bypassing the RV’s electrical system entirely) to rule out connection/grounding/voltage spike issues
- Verify the wire size is correct or exceeds the manufacturer’s recommendation (provided in the manual)
- Verify all electrical connections are tight and the fuses are seated and in working order
- Ensure the refrigerator is the only item on the circuit (to prevent other appliances from dropping the voltage or causing voltage spikes)
Step 7: Check the compressor windings
- On 1996 or later BD35/BD50 compressors, remove the screw in the font of the controller
- Remove the three pin connector
- Using a multimeter, measure the resistance (in ohms) between the pins, which should be approximately 1.5 to 3 ohms
- There should be no continuity between any pins and the compressor’s metal shell
Here is a summary of the LED fault codes:
- No LED illumination: thermostat is open / no power
- One LED flash, four second pause: electrical resistance problem, low batteries, power supply concerns, voltage spikes
- Two LED flashes: fan over current cutout (short in wire?)
- Three LED flashes: excessive torque required to start the compressor… common issue if you turn the unit on and off too quickly or if the refrigerant has been overfilled, last case would be a compressor rotor lock up which is uncommon with these highly reliable Danfoss compressors
- Four LED flashes: compressor motor not reaching sustained controlling speed above 1850 amp quick enough (evidently this is a really rare issue but sometimes tampered refrigerant lines can cause this error code if air is in the lines, etc). Verify the capillary tubes are not iced over causing a restriction in working fluid flow.
If the above steps do not identify a problem you may have a faulty controller. You’ll need to send it in to have it tested on a known functional unit and replaced if the same problem is replicated on a working unit in a shop.
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