This page uses Norcolds words to compare ARP versus Norcold Recall and why Norcold leaks result in RV fridge fires that may have been prevented.
What does the ARP Control do? When installed and maintained properly, the ARP Control helps prevent catastrophic conditions by not allowing the cooling unit boiler to experience temperatures that permit the fluids in the system to overheat. These temperatures generally do not exceed 400F. If the fluids in the system are maintained at proper temperatures excessive thermal stress is not allowed to create conditions that can lead to a leak and the possibility of a resulting fire.
"ARP Control solves problems with the refrigerator whereas the Norcold control solves a legal issue.
If these fridges were in airplanes, the FAA would prohibit them to fly without the ARP Control."
Quoted from Retired Rolls Royce Avionics Engineer - Indio, CA 2013
Norcold took the first step to try and solve the issues that resulted in cooling unit failures. The 2 steps that Norcold took attempted to address the issues that result in fire. We at ARP LLC took the next step; we found the control parameter that protects the fluids within the cooling unit. Please click for ARPC LLC policies.
Read on to understand why you will need a ton of cure without the ARP Control!
Please click here to see the science behind boiler temperature regulation.
This image is of a letter from Norcold which describes the Norcold 1200 series recall kit function. Some potential customers and a few RV repair technicians have stated that there is not a difference between the ARP Control and the Norcold Recall. This is just not true; the proof is in the correspondence.
Following we will use the right use of reason backed by science to help RV owners understand the difference between the ARP Control and factory recalls and repairs. We will include Norcold's correspondence so that the facts are gleaned clearly.
The Norcold letter above states this about the function of their recall kit:
Norcolds Recall Kit 634737 does not and cannot address off-level tilting conditions. Norcold's Recall Kit 634737 functions only to address extremely limited, catastrophic conditions in which liquid is drained from the system (e.g. as a result of a leak). Heat input to the cooling unit is not adjusted until a sensed temperature of over 800°F. Such temperatures are only experienced at the location of the Norcold sensor if the cooling system experiences a leak.
Clearly one cause of an RV fridge failure is a leak. The effect of this type of failure is either the complete failure of your fridge, or possibly in the worst case a fire. Why go there? Would it not make more sense to address one of the known root causes of failure as will be explained in the next section?
Following is the relevant contents of a letter sent to the NHTSA in the year of 2002. A discussion of the ARP Control with regard to the text will follow. References are used (R1, R2, R3,...) to relate the context of the letter to the ARP Control function and solutions.
Norcold Letter: We have determined that a defect relating to motor vehicle safety exists in some specific gas absorption cooling units used on refrigerators supplied by Norcold to manufactures of RVs.
R1) As presently understood, the nature of the defect is low cycle fatigue failure in the section of the cooling unit which generated the refrigerant.
R2) The potential safety problem is induced by elevated heat during operation in the AC electric mode.
R3) The consequences of this fatigue failure can lead to the liquid solution slowly leaking from the sealed pressurized cooling unit through a small crack which could occur from the thermal expansion created from the AC heater design. If a leak occurs the cooling performance of the refrigerator will deteriorate requiring a replacement of the cooling unit.
R4) If the refrigerator continues to be operated after the majority of solution has leaked and solution circulation has ceased, the heat source can generate very high temperatures.
R5) At that time, the steel material can soften and rupture.
R6) If the pressurizing gas is still in place when the rupture occurs, hydrogen gas may be expelled and can under extreme conditions, be ignited by the high temperatures thereby possibly causing a fire.
R7) Tests indicate that refrigerators will exhibit signs of unacceptable cooling performance prior to the unsafe condition arising. Field experience reflects that consumers have replaced the affected cooling unit under our standard warranty program before a safety problem actually arose.
R1) Clearly, at the time of the writing of this letter, an assumption was made, and in the course of time a program was implemented to resolve this described structural issue. But, 12 years later it is clear that the initial assumptions were only a small part of the big picture.
R2) Norcold does acknowledge the need for the ARP Control in this statement. "Elevated heat" is a major contributing factor that leads to excessive stress on the cooling unit boiler assembly. The ARP control limits the temperatures in the boiler when installed and maintained correctly.
R3) Clearly, the Norcold engineers understand that thermal expansion results in leaks in the cooling unit. Thermal expansion is limited by limiting the temperature of the boiler assembly.
R4) And here we see the proof that the ARP Control is needed. Anytime the solution circulation has ceased, the boiler (generator) can and will produce very high temperatures. This is the crux of the matter, the ARP Control is designed to limit boiler temperatures.
R5) At 800 degrees combined with a typical pressure in a cooling unit being 350psi, this is dangerously close to the yield point of steel. What is the yield point? For a cooling unit the yield point is when the pressure inside the cooling unit is high enough to result in a failure of the steel vessel.
R6) This is a well known fact now.
R7) Clearly, operation of the cooling unit while the fluids are not circulating properly, such as during off-level operation, lead to unacceptable cooling performance. The ARP Control is proactive in prevention of operation of the cooling unit while the fluids within the cooling unit are not circulating. Thus, the ARP Control is the best method to prevent unsafe conditions from arising in the first place. Regarding the last sentence, now hindsight brings this statement into question.