RV Doctor Column RV Doctor #254 Dear RV Doctor,, I have a Suburban furnace. I have replaced the limit switch, module board, cleaned the orifice of the main burner, replaced the gas valve, replaced the electrode, cleaned the furnace thoroughly. The furnace comes on only after the third try. Could the problem be with the relay time delay switch? That was not replaced. W. Leslie, (Altoona, PA) William, I doubt if the relay is at fault. If the blower rotates and the unit fires at all, it means the contacts are indeed closing. Since you have replaced just about every component, (perhaps needlessly), the problem probably lies elsewhere. You didn't state how old your Suburban is, but I would investigate these areas; be sure the squirrel cage, (blower assembly), is clean and balanced. It is best to run the furnace on the bench to verify how smoothly the cage rotates. Occasionally, dust and dirt will collect in the corners of the fins, adding weight thereby impeding the movement of the blower. Sometimes it will throw the whole assembly out of balance resulting in the blower not turning fast enough to satisfy the air prover switch. Clean out all particles of dust and dirt. The air prover switch, sometimes referred to as the sail switch, is position within the path of the air produced by the blower. If the blower does not rotate fast enough or if the air prover switch is faulty, erratic operation will result. The fact that it does eventually light though, makes me think the blower fins could be clogged with dust. A final item to check is the space gapping between the electrodes on the ignitor. Be sure the gap is correct for your model. If the electrode assembly contains three probes, the gap between the ground and the spark ignitor should be half of the gap between the ground and the flame sense probe. Reposition only the ground probe to achieve the proper gap. Additionally, the spark should appear well within the flow of LP once the valve opens. Dear RV Doctor, We have a 1978 Kit camper. Two questions actually: Do you leave the water pump switch on when in a campsite? Does it draw any power from the battery when not in use? And, we have two house batteries. Will they recharge when the vehicle is running? We have an isolator for the truck battery. Thank you for any assistance. T. Sherlock, (Vancouver, BC) Tim, Yes it is fine to leave the pump on when you are in and about the RV. But keep in mind, the pump will start at any "demand" for water, I.E., when you open a faucet, flush the toilet or spring a leak at any fitting. The pump only draws battery current when actually running. The isolator method of dual battery charging is also my preference so long as the alternator, the isolator, the batteries and all conductors are sized correctly for the system. Dear Gary, What can you tell me about how manufacturers vent the battery compartment when it is inside the coach, (as opposed to under the hood)? Does anybody bother? If they do, do they use a 12-volt fan or 110-volt AC fan? If it is12-volts, how is the fan controlled? Does anybody talk about this topic in an RV book? I have called some RV electric suppliers, by didn't get much of an answer. I'm revamping the 12-volt system in my 1972 Midas 21 foot class C which had no venting for the coach battery. Thanks for your help. P Malec, (Laurel, MD) Paul, Indeed all battery compartments are required to be sealed from the interior and vented to the exterior of the RV. This is accomplished using a few methods, none of which would utilize an electric fan, (gotta watch those sparks in a battery compartment). Pre-made, self-contained battery compartments installed through the side wall of the RV are already compliant with the code by having mechanically sealed seams on the box itself and a door vented at the top and the bottom. Boxes constructed of wood should be metal lined and the seams sealed with silicone or another type sealant. When the battery must be installed fully inside the RV, in a closet or under a dinette bench for example, many makers use a plastic battery box equipped with a removable yet sealable lid with a 2-inch vent hose that exits through the side wall of the coach. The vent hose must originate in the box lid above the battery and exit the side wall at a point above the battery box. In other words, the vent hose cannot form a "U" which can trap vapors. The box seals around the conductors when the lid is secured. You can probably order a sealed battery box from your local dealer. There are many distributor catalogs at his disposal to find most of the components you will need. Dear Gary, Do you have any recommendation for the absorption refrigerator? Do I keep it running all the time or only when needed? My first refrigerator did not last a very long time and I turned that one on only when needed. R. Rodriguez, (Miami, FL) Rafael, The important items to remember when using your RV absorption refrigerator include; operating the unit only when completely level, (while sitting still), the circulation of fresh air around the absorber coils and condenser fins at the rear of the refrigerator and the proper supply of LP and/or electricity. Most experts agree operating the refrigerator when the RV is not being used simply adds to the wear and tear of the unit. It basically will shorten the working life of the refrigerator. There appears to be no viable benefit to leave the refrigerator operating during non-use periods. It's simply best to turn it off, clean the unit thoroughly and store it with the door propped open. Stuffing newspapers inside the food sections during non-use will help eliminate any food odors that may have permeated the interior. When it's time to go RVing, prepare the refrigerator properly by cleaning the burner and flue assembly and checking the LP pressure, insuring it is set to 11.0 inches of water column. Maneuver and level the RV so the freezer section or the shelf in the freezer is truly level and begin refrigerator operation with it empty so it will be pre-chilled prior to storing the food. Avoid using wide dishes or platters in the refrigerator that will inhibit the convection movement of air inside the food storage section. Also avoid opening the door when not necessary. By following the above guidelines, the RV absorption refrigerator will provide many years of satisfying service.
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