FRIDGE ASSIST

Tips for simple problem resolution:  (Applies to all brands / types of DC compressor refrigerators / refrigeration)

Compressor fails to start or cuts out prematurely:

By far the most common problem DC refrigerators have is the 12VDC power supply, and not  the actual compressor or MDM  itself!

 

To explain:   All of these DC compressors have a ('black box') Motor Driver Module, (MDM) which inverts the supplied DC power into 3 phase AC power to drive the 3 phase AC compressor motor. These MDM's are of two very different types, DOL and Soft Start.

 

The DOL (Direct on Line) module causes a massive current inrush (can be up to 7-8 times run rate) as it tries to take the compressor from stationary to run speed virtually instantly while the Soft Start MDM slowly starts the compressor without any inrush current..  

 

If the voltage drops away too much at a start attempt or when running, the MDM's low voltage cut out prevents the module driving the motor from starting or running.  

This shut down because of a poor power supply, is usually due to either a defective, or faulty battery, battery to MDM wiring, or faulty devices along that circuit like bad *spade terminal connection, switch or overload.  (*Specially spades terminals - & + on the MDM)  

 

If unit won't run, below is the easiest and industry recognised way to identify if voltage drop is the problem or if the MDM is faulty.. 

Voltage drop test: (Above)                                                                                                   Also see: https://www.ozefridge.com/news                                                                             

Using a good multi-meter connected to the negative and positive terminals (- & +) on the MDM as shown above, read the voltage before and when the compressor starts or attempts to start. 

The voltage reading with no load, before the compressor starts is meaningless but do note that no-load voltage.

Next, continue to monitor the voltage as the compressor starts or attempts to start. If this voltage drops away by say a volt or more or below 10 volts then that is confirmation that most likely the power supply is the problem and that the compressor and MDM are not at fault. Again with multi-meter, check again as above, from MDM back to the battery, testing at each terminal access etc.  

Thermostat test:

Terminals C & T are the thermostat switch connections. (Bottom and third from bottom terminals) If there is adequate DC power to the MDM but the compressor will not start or attempt to start, it may be because the thermostat (switch) is faulty. 

To check simply bridge the terminals C & T and if the compressor runs then the thermostat is faulty. If an older system with mechanical thermostat, consider replacing with a digital type for far more accurate control and temperature read out. (On Ozefridge systems simply switching to 'Manual' on controller panel to by pass the thermostat, will achieve the same)

Fan Corruption:

Most DC refrigeration units use small fans. If the fan draws greater than half an amp (6 watts) the MDM will shut the system down.  These fans are also driven via their own internal micro processor, a processor that if faulty can corrupt the MDM, therefore if fault persists try disconnecting the fan and if the compressor then runs, switch off and replace the fan.. most likely a type 100-25 12VDC.,  2.5 to 4.0 watts  (Neither of these issues concern Ozefridge systems as their fans are powered via a relay and this simply can't occur)  Note: Relay switching is essential if an addition fan or fans is to run in parallel with the compressor.

 

Voltage Spikes:

Voltage spikes or 'High voltage Transient Spikes' are usually very high voltage, (can be in the 1000's of volts, but negligible current) , very rapid / short lived and totally unpredictable. 

These high voltage spikes can damage electronic items like MDM's, Fan drivers and

digital thermostats due to arcing.  (Arcing like a spark plug!)

 

However while they are high voltage and can damage electronics, they are not the cause

of failure to start.

 

(The C / forums grandstanding guru's talk about 'Low voltage Spikes' preventing motor                                                                         start up is absolute nonsense!  Motor start failure is usually due to collapsing voltage as                                                               

the start load is applied, easily detected with a good multi-meter as described above) 

 

At Ozefridge we fit a Voltage Clamp, (AKA Zorb, AKA Spike arrestor), to all systems as

standard and highly recommend all users fit one of these very inexpensive devises to 

help protect all electronics coupled to the DC power supply.  We use a P6KE33CA - TVS

Diode, P6KE3 Series, Bidirectional, 28.2 V, 45.7 V, DO-204AC, 2 Pins. 

Refrigerant gas charge:

If a system is running but the evaporator or eutectic plate is not or only partly frosting, it is most likely that the system has lost refrigerant gas. Usually loss of gas causes low or high power consumption rate. (High if air contaminated. (evacuation and new filter essential) 

If a system needs gas it is because it has a gas leak, a leak that must be identified and repaired. After repair the filter dryer should be replaced and the system evacuated preferably for several hours before adding fresh refrigerant gas.

 

On the Ozefridge system simply press the arrow down button to monitor the condenser temperature (High side pressure).

When recharging, run the unit and only slowly allow refrigerant in sufficient to maintain a 12 - 14  PSIG suction. . Once this pressure is maintained without addition, close off and leave running.   Fine tune later once temperature lowers and settles.

Only connect your gauge suction line (blue) to evacuate/ charge system. Do not fit high side gauge. (Red liquid line)

Filter Dryer:

Unfortunately most small refrigeration systems are fitted with cheap 'spun copper dryers'. These items have no felt filter pad unlike the proper filter dryer type 032 (as used by Ozefridge).

Copper spun dryers only have a screen. The screen doesn't collect the fine gunk that rubs off the desiccant beads or sludge that can form as a result of contaminated oil, eventually to possibly cause capillary or TX valve restriction. 

If repairing a leaking system we suggest fitting a proper type 032 or 052 flared filter dryer mounted vertically, exit downwards. If this can't be fitted in place of the old copper type, then simply leave the copper one in place and fit the proper filter dryer as well. 

Compressor Oil: 

Most systems use R134a refrigerant with one of the Polyolester oils. If a gas leak occurs on the system low side (evaporator- compressor) the system is likely to have been running at negative pressure (vacuum) Moisture and other gunk can be drawn into the system specially if the leak is on the once frosty / wet evaporator. This contaminant will collect in the compressor oil with the likelihood of causing on going problems if not replaced. Oil is cheap compared to replacing a compressor later and the downtime.

News from Ozefridge: 

We are constantly researching ideas and seeking ways to improve our products and our clients experiences. We appreciate user feedback and ideas as this forms the basis and direction for much of our ongoing research.

The very latest.. 

As a major manufacturer of DC refrigeration systems, we and others in the industry have known for a long time that the vast majority of service issues are power supply related and not the fault of the refrigerator or refrigeration system.

This power supply failure is often difficult to convey as the voltage on the ships voltage meter may indicate that all is well.

 

It is ONLY the voltage at the fridge unit and ONLY while it is running, or attempting to start, that is relevant. 

Voltage without any load means NOTHING. 

So, something new!

                                                                      Modern technology has now provided us with a tiny sealed, digital volt meter that can                                                                            read voltage at the unit where it matters!

                                                                      This meter is now fitted standard to all Ozefridge systems as seen here (Left).

                                                                      This allows monitoring of battery supply and will see the digits flash if the voltage                                                                                     drops below 11.5 VDC (Effectively flat battery or defective supply line).

                                                                       To be able to monitor voltage supply at a glance allows users to become familiar with                                                                             their power  supply and recognise any deterioration before it becomes an issue.  

                                                                       The addition of this voltage monitor along with other auto resetting fail-safe                                                                                            technology and spike protection, provides maximum system protection.                  

                                                                       

                                                                        Testing for voltage drop causing compressor to fail at startup may be identified by this                                                                            meter but will still need to be confirmed as described at our 'Fridge Assist' page using a                                                                          digital multi meter.

NOTE: In some countries including Australia, refrigerant gases can only be legally handled by licensed persons.