House Calls with the RV Doctor
By Gary Bunzer
Dear RV Doctor:
I bought a heat strip for my Duo-Therm roof air-conditioning unit and I don’t know where to install it. I know it is the correct type for my unit, but I can’t quite figure out where it goes.
John Justice, Lake Ariel, Pennsylvania
John, first you must remove the plastic ceiling air distribution box. Do so by removing the return air grilles covering the filters (some units may be equipped with a single grille and filter). Once they are removed, you should readily see two or more screws securing the plastic housing to the A/C plenum. Depending on the exact model Duo-Therm, there may be another screw behind a plastic plug on the air box itself. Very carefully pry the plug out with a small screwdriver and remove all the mounting screws. Next, remove the ceiling distribution box to expose the metal A/C plenum. The heat strip assembly installs directly below the air discharge opening, which is that opening going up into the rooftop unit. You’ll see small mounting holes in the plenum corresponding to the screw locations on the heat strip. Position the heat strip directly under the discharge duct so the screw holes line up with the holes in the plenum, and secure it using the supplied sheet-metal screws. Plug the electrical connector on the heat strip into the existing receptacle on the air-conditioning control box. Typically, the air box is notched to allow the harness to pass through it, but you may have to slit the foil or insulation or knock out a plastic plug. Once you have made space for the power harness, you can remount the air distribution box to the plenum. Realize that add-on heat strips may take the chill out of the air, but they will not sufficiently heat the entire motorhome.
Cooling Core Color
Dear RV Doctor:
I’m installing an absorption refrigerator in a bus conversion, and I want to clean and paint the rear coils of the cooling unit. What color should I use? Flat black? The original color appears to be gray.
R.W. Clawson, Thorndale, Texas
I’ve seen black, gray, and various shades of green used to paint the cooling tubes on absorption refrigerators. The color is totally up to you. Cooling units are painted only as an aesthetic practice. In reality, they do not have to be painted at all. It’s just what we’ve come to expect. If you decide to paint them, you must use high-temperature paint, as portions of the cooling core can become quite hot during operation.
Take care when preparing the coils for painting. Make sure the refrigerator is turned off and the boiler section of the cooling unit has cooled off. Do not use a very coarse wire brush to remove corrosion. Gently sand light rust, but do not sand into the metal tubing itself. Take special care around welded joints in the tubing. Do not twist or bend any portion of the tubing. Be aware of any exposed LP-gas and electrical control components; be sure to protect them from overspray. Paint only the tubing surfaces you can see.
Fixing Furnace Faults
Dear RV Doctor:
I have a 2001 17,000-Btu Suburban propane furnace in my RV that will not light when the ambient temperature is cold (45 degrees Fahrenheit or less). I have checked the battery and have sufficient power. The fan comes on but the ignitor never tries to ignite. When the outside temp is above 50, the furnace will start right up. Also, after it starts once, it will restart without fail as long as the unit is not allowed to cool. Could this be the sail switch or control board? Obviously, the thermocouple works, as it lights when warm.
Reed Meredith, Mount Crested Butte, Colorado
Reed, based on your statement that “the fan comes on but the ignitor never tries to ignite,” we probably can rule out an LP-gas delivery problem related to the colder weather. But electronics can be very problematic in colder weather, though the problem usually is related to faulty or dirty connections. Try this: unplug the connector to the control board on the furnace and carefully inspect both the plug and the board traces for corrosion or oxidation. Temperature and humidity changes can greatly impact corroded or oxidized connections and their ability to conduct electricity. If there is any corrosion or oxidation on the board, temporarily clean it off using a standard pencil eraser. Be sure to blow away any eraser debris. The plug is best cleaned using a contact cleaner and protectant; I favor the products of CAIG Laboratories. You also can scrape it off, but be extremely careful not to bend the connectors in the plug. Once you have inspected and cleaned the contacts, firmly reseat the plug onto the board and make sure it is tight.
Next check all other connections to make sure they are clean and tight, including the ground connection. It is possible that your control board has an open solder joint or trace that is opening and closing with temperature changes, but this would be unusual for the temperatures you mention.
If you still have problems after performing this maintenance, I would suggest the board be tested on a bench board tester. Weather also could cause the gas solenoid valve to stick, but since you have stated that the ignitor never fires, chances are the gas valve is okay. It is possible the sail switch is heavy with lint and needs cleaning, but typically this would result in the problem happening every time the unit tried to fire. It is, however, important to have the furnace cleaned and serviced annually, which includes cleaning and testing the sail switch.
Dear RV Doctor:
I just received a copy of your Woodall’s RV Owner’s Handbook; great book by the way! My problem is the oil reservoir on the hydraulic pump for the slideouts. It is leaking. I didn’t see anything in the book about the hydraulic system. Could you tell me where I could find info on this subject?
Les Hewston, Columbia Falls, Montana
In all honesty, Les, there are some things on your motorhome that should not be attempted by the average RVer. It’s my opinion that the hydraulic system is one of those areas best left to the professional service technician. Many leveling and slideout systems are quite sophisticated and require specialized training for comprehensive troubleshooting and repair to take place. Couple this with the fact that many proprietary systems are so unique that no generalized procedures will truly suffice. If your system is manufactured by a major supplier, such as HWH, you can order or download data based on your specific model directly from them. Look on or near the control panel or the reservoir itself and locate the brand name. If necessary, give them a call to see what literature is available.