Burping A Dometic
Q: I have a 1993 Pace Arrow with a RM2807 Dometic refrigerator. Two years ago, I burped it (turned it upside down) when it would not cool below 50 degrees Fahrenheit. I understand that the reason for burping it is so the chemicals can settle into the top portion and then run back to the bottom when the unit is placed upright again.
The refrigerator worked fine afterward, but on an extended trip this summer it got to where it would not cool below 50 degrees again. I purchased a small fan and put it in the rear to better dissipate the heat. It brought the temperature down to 40 degrees, and we came home. I turned the unit off and unplugged the fan. After approximately a week, I turned it back on without the fan, and it appears to be working as it should.
I am confident it had a plugged cooling coil, because the upper part was cool and the bottom was hot to the hand. I should mention, too, that the freezing unit has never given us any problem.
Is there an advantage to periodically turning off the refrigerator to allow the chemicals to completely cool down or whatever they do?
Johnnie Dekle, F217562
A: The scenario you describe is typical of a refrigerator that has some debris floating around in the refrigerant. It could be left over from the manufacturing process, welding slag, ferrous corrosion from the ammonia, or even sodium chromate crystals from overheated refrigerant. Regardless, the debris has accumulated someplace and is restricting the circulation, thus reducing the amount of cooling available. First evaporation takes place in the freezer and secondary evaporation in the food storage compartment, so the reduced cooling will be noticed first in the latter.
When you “burp” the unit, the refrigerant is used to back flush the evaporation chambers, and thus rearrange the obstruction to another location “” possibly indefinitely, but probably not.
Sometimes the cooling unit can be turned off for a period of time, and this will take the pressure off the evaporators and allow the obstruction to clear itself.
I can see no advantage to periodically turning off the refrigerator, but I also see no disadvantage.
Brake Loss Revisited
Q: I read the letter about Mr. Richert’s brake loss problem on his Winnebago with a Ford chassis (September 2001, page 24). I have the same brake loss problem on my 1998 Cruise Master, built on a Chevrolet chassis. Whenever the temperature is above 90 degrees Fahrenheit and traffic is stop-and-go, my brake pedal goes to the floor, leaving me without brakes.
I took the coach to a non-dealer “” none of the GM dealers in my area were familiar with this problem or with motorhomes “” and the technician bled the brakes. This helped somewhat but was not a fix. He also checked the fluid for water and contaminants; there were none.
Larry Dietrich, F158272
A: Mr. Richert, you might be able to use this suggestion concerning your brake loss problem. I have a 1990 type C coach on a Ford chassis, and I have had the same problem that you described. Experienced mechanics told me that the cause of the problem was that the front caliper pins corrode and drag. (When the chassis is not used daily or is used in the Northern weather belt, the corrosion happens faster.) The pads fail to retract on the pins and then drag on the rotors, which causes heat. The more they drag, the hotter they get, until sufficient heat is transferred through the piston to the brake fluid, which then boils, causing brake loss. As soon as the fluid cools, the brakes work again.
Changing the fluid, as suggested in a previous column, might help, but taking the pins out, replacing them with new ones, and lubricating them is more likely a cure. Also, the pistons should be changed from steel to phenolic, and it is probably a good idea to replace the caliper assemblies as well. On later model years, Ford changed the design and used stainless-steel pins, eliminating this problem.
Scott Kostenbauder, F164924
Poughquag, New York
Q: I also have a 1990 motorhome with a Ford chassis, and I had the same brake loss problem as Mr. Richert. Ford Motor Company did issue a recall on the brakes.
What causes the problem is this: on a hot day in slow traffic, the heat builds up under the insulated engine cover. The brake master cylinder is located beside the engine next to the exhaust manifold. The brake lines get so hot that the brake fluid boils.
A Ford technician wrapped my lines with special insulation material. It helped, but on a really hot day, I still have a problem.
John Willson, F92404
Interlaken, New York
A: First of all, let me say this: if you should ever lose your brakes as a result of heat absorption, always have the fluid drained, flushed, and replaced, using DOT #3 or better (check your owners manual). If the fluid should overheat, it will be contaminated.
All of the above-mentioned causes are possible contributors to overheating the brake fluid. If you are experiencing this problem, the first thing to do is to insulate the brake lines against exhaust heat. After that, inspect your rotors for overheating (they will be tinged blue if they’ve become overheated). If this has happened, the rotors should be removed and replaced or at least turned on a lathe to true them up (the heat may have caused them to warp).
Check all components to be sure each is doing its job to factory specifications. Use the appropriate lubrication product (per the owners manual) to lube the moving parts correctly. Also, check with your local Ford dealer for any recall information; be sure to have your vehicle identification number (VIN) handy when you make this request.
I checked with Ford about this problem, and found that no recalls were issued for brakes on 1990 E-chassis (the recall that Mr. Willson referred to may be 92S44, but that applies only to certain 1988 through 1991 F-250/F-350 trucks). According to Ford, a technical service bulletin (TSB 91-20-08) for 1988 through 1991 E-250, E-350, F-250, and F-350 vehicles built prior to May 1, 1991, provides directions on updating parts on the brakes to make them more resistant to fade under high gross vehicle weight conditions on steep downhill grades.
Winterizing Water Systems
Here is a reminder to those who use RV antifreeze to winterize their water systems at home or in their coach: make absolutely certain that you are using only non-toxic antifreeze designed for drinking water systems. Windshield washer fluid and even engine antifreeze often come in similar containers and colors and can be mistaken for non-toxic antifreeze. This mix-up can be disastrous, both health-wise and financially. Make certain that the label of anything you place into your fresh water tank says it is designed for that use.
If you have an opened container of antifreeze that has been sitting around since last winter, it might be good to place that into the traps and holding tanks instead of the fresh water tank, just in case someone placed something else into the bottle over the summer. Also, you may wish to save the label off the antifreeze bottle until next spring so that you have directions for flushing the water systems at that time.