Red Seal RV Service Technician cheat sheet

Personal protective equipment for RV work: safety glasses when drilling or cutting sealant, nitrile gloves for LP leak solution and black-tank work, hearing protection near generators and air tools, and respiratory protection when spraying two-part foam or lacquer.

LP gas is heavier than air (specific gravity about 1.5 relative to air); leak checks use a soapy solution or an electronic combustible-gas detector, never an open flame.

Battery safety: remove the negative/ground cable first and reconnect it last; lead-acid off-gassing is explosive, so charge in ventilated space and neutralize acid spills with baking soda.

Carbon monoxide is colorless and odorless; never run a generator, engine, or catalytic heater in an enclosed shop or a closed coach, and test CO alarms before returning a unit to the customer.

Torque values are specified dry or lubricated and are invalid if the fastener is oily or the threads are damaged; use a calibrated torque wrench and re-verify calibration at the interval the manufacturer states.

Ladder and roof safety: use a stable ladder rated for the load, keep three points of contact, and treat RV roofs as fragile - walk on rafters or use plywood load-spreading panels.

Electrical lockout: disconnect shore power, turn off the inverter and battery disconnect, and verify zero voltage with a meter before working on 120 VAC circuits.

Waste handling: drain black tanks only at approved dump stations; store and dispose of used oil, coolant, and solvent per local regulations, and keep a spill kit on hand.

Documentation practice: record complaint, cause, correction, parts, and labor on the work order; a repair without a documented cause cannot be warrantied or defended.

Ohm's law: V = I × R; power: P = V × I. A 12 V load drawing 8 A has 1.5 Ω resistance and consumes 96 W.

Voltage drop in a DC conductor: VD = (2 × L × I × R_conductor) for a round trip; keep total drop under about 3% (roughly 0.36 V on a 12 V circuit) or equipment misbehaves.

Battery capacity: amp-hours are rated at the 20-hour rate; two 6 V golf-cart batteries in series give 12 V at one battery's Ah rating, while parallel connection adds Ah at the same voltage.

State of charge for a flooded lead-acid battery at rest (about 12.6 V = 100%, 12.4 V = 75%, 12.2 V = 50%, 12.0 V = 25%); recharge below 50% to limit sulfation.

Converter/charger output should be checked at the battery terminals with loads off; a reading near 13.6 V float or 14.4 V bulk is normal, and a low reading indicates wiring drop or a failed converter.

120 VAC shore power: 30 A service is one 120 V leg (3-wire), 50 A service is two 120 V legs plus neutral and ground (4-wire) giving up to 12,000 W; a 50 A to 30 A adapter feeds only one leg.

Ground-fault and polarity: an open ground, reversed polarity, or neutral-ground bond in the coach will trip a pedestal GFCI; the coach bonding point is at the panel, not downstream.

Inverter sizing: continuous rating must exceed the sum of concurrent AC loads, and surge rating covers motor starting; undersized DC cable causes low-input shutdown.

Fuse and breaker sizing protects the conductor, not the appliance; replace only with the same rating, and check that the wire gauge matches the overcurrent device per the manufacturer's chart.

LP cylinder relief valves and the 80% fill rule: a 20 lb cylinder holds about 4.7 US gallons of liquid, and the fixed liquid level gauge or bleed valve indicates full.

Cylinder identification: DOT cylinders are refillable and recertified on a schedule (typically 12 years from manufacture, then every 5 years); ASME horizontal tanks are permanently mounted and not recertified the same way.

Regulator stages: a two-stage system uses a first-stage regulator at the cylinder (about 10 psi) and a second-stage at the coach (11 inches water column, about 0.4 psi) for appliance supply.

Manometer testing: with appliances off, the system should hold pressure with no drop during the timed leak test; a drop indicates a leak at a fitting, hose, or appliance valve.

Leak detection uses soap bubbles or an electronic detector; LP has an odorant (ethyl mercaptan) added, and odor fade can occur in new or long-empty cylinders.

Combustion air: appliances need a supply of combustion air and venting; a yellow lazy flame, sooting, or lifted flame indicates wrong orifice, low pressure, or blocked burner/vent.

Appliance gas pressure test ports (furnace, water heater, refrigerator) read at the manifold; readings outside the data plate specification mean regulator or orifice problems, not a bad control board.

LP detector placement is low in the coach because the gas is heavier than air; the detector has a limited service life (often 5-7 years) and must be replaced, not just cleaned.

Never use a flame to test for leaks, and never plug a vent or combustion air opening; a CO alarm sounding with an LP appliance running means shut the appliance down and inspect the heat exchanger and vent.

Fresh water pump diagnosis: a pump that runs continuously usually indicates a leak, a failed check valve, or an air leak on the suction side; a pump that short-cycles points to a waterlogged accumulator or bad pressure switch.

Winterization: bypass and drain the water heater, blow lines with regulated air (about 30-40 psi) or fill with potable antifreeze, and pour antifreeze into P-traps and the toilet; a dry water heater tank must not be powered.

Water heater anode rod: in a Suburban-style steel tank the magnesium anode sacrifices itself; when more than about 75% consumed it must be replaced or the tank corrodes.

Black tank vs gray tank: black holds toilet waste and uses a 3-inch dump valve; gray holds sinks and shower through 1.5-inch lines. Dump black first, then gray to rinse the hose.

Holding tank sensors read false when coated with waste or TP; cleaning and sensor replacement are the fix, and a tank flush fitting helps.

Venting: a P-trap protects against sewer gas, and an air admittance valve (chek valve) lets drains flow without a roof vent; a gurgling drain often means a stuck AAV.

PEX and fittings: crimp rings and expansion fittings require the matching tool and gauge; a proper crimp is checked with a go/no-go gauge, and sharkbite-style push fittings need a square, burr-free cut.

Toilet seal: a leaking flush ball or blade seal causes the bowl to lose water and allows odor; the seal and the floor flange gasket are separate parts.

City water inlet has a check valve to prevent backflow into the coach; a failed check valve lets the fresh tank fill when connected to city water.

Air conditioning diagnosis starts with airflow: a dirty filter, blocked return, or crushed duct reduces capacity and can freeze the evaporator coil; verify delta-T across the coil (typically 15-20°F/8-11°C).

Refrigerant charge is checked by superheat or subcooling per the manufacturer's chart, not by gauge pressure alone; a low charge shows low suction pressure and high superheat.

Roof air conditioners are sealed systems on many models; if no service ports exist, refrigerant work requires adding access valves or replacing the unit per the manufacturer's policy.

Furnace sequence: thermostat calls for heat, sail switch proves blower airflow, then the gas valve opens and the igniter lights the burner; a repeated three-try lockout points to sail switch, igniter, or gas pressure.

Sail switch and limit switch are in series safety devices; a dirty blower wheel or restricted duct trips the limit and shuts the burner down.

Heat pump vs furnace: a heat pump reverses the refrigerant cycle for heat and loses capacity in cold weather; below its balance point the gas furnace takes over.

Ducted systems require balanced static pressure; adding or blocking registers changes airflow and can cause coil icing or high-limit trips.

Condensate: roof AC units drain condensate onto the roof or through a drain cup; a plugged drain pan overflows into the coach ceiling.

Ventilation: roof vents and fans must be open to exhaust moisture; a sealed coach with the fan running pulls air from appliance vents and can backdraft the water heater or furnace.

Roof types: EPDM rubber, TPO, fiberglass, and aluminum. Sealants and lap sealant must match the membrane; petroleum-based products damage EPDM.

Lap sealant (self-leveling) is used on horizontal roof seams and around vents; non-sag sealant is used on vertical surfaces and sidewalls.

Water intrusion path: check roof seams, clearance lights, window frames, slide-out flanges, and the front/rear cap seams; a leak often shows up far from the entry point.

Delamination is separation of the exterior skin from the substrate; it appears as bubbles or a dull thud when tapped and usually follows long-term water intrusion.

Butyl tape goes behind frames and vents as a gasket; sealant goes over the fastener heads and edges. Both are needed; one does not replace the other.

Fiberglass repair: grind to a taper, clean with the specified solvent, then apply resin and mat or a filled fairing compound; gelcoat must be sanded and buffed after cure.

Fasteners into sidewalls must hit framing or use proper expansion anchors; a screw into 1/8-inch luan alone will pull out under load.

Roof load: AC units, solar panels, and roof racks need to be supported over rafters; a walkable roof is rated by the manufacturer, not by appearance.

Sealant inspection interval is typically every 6 months; re-seal before cracks open, and remove old sealant rather than layering new over failed material.

Trailer weight terms: GVWR is the maximum loaded trailer weight; GAWR is per axle; tongue weight is typically 10-15% of trailer weight for a conventional trailer and should not exceed the hitch or receiver rating.

Tow vehicle ratings: GCWR (gross combined weight rating) limits the total of tow vehicle plus trailer; payload rating limits passengers, cargo, and tongue weight, and is often the real limit.

Weight-distributing hitch: spring bars transfer tongue weight to the trailer and front axle; the setup is verified by measuring front fender height before and after hitching.

Sway control and friction sway bars reduce oscillation; sway is worsened by too little tongue weight, crosswinds, and speed.

Fifth-wheel and gooseneck hitches place the pin over or slightly ahead of the rear axle; the pin box and the hitch must be rated for the trailer's GVWR.

Trailer brake controller: electric brakes need a controller set so the trailer stops with the tow vehicle without locking the wheels; a breakaway switch and battery are required on trailers over the legal weight.

Tire date codes: the DOT code's last four digits give week and year (e.g., 3521 = week 35 of 2021); RV tires age out (often 5-7 years) before tread wears out.

Wheel bearings: repack at the manufacturer's interval, check for play and heat after towing, and never mix grease types in a bearing.

Alignment and suspension: uneven tire wear on the inside or outside edge indicates camber or toe problems; a pull can be a brake drag, tire, or alignment issue.

Slide-out types: electric rack-and-pinion, cable-driven, and hydraulic. Each has its own manual override procedure; know the override before the slide fails in the out position.

Slide-out synchronization: cable and rack systems must be timed so both sides move evenly; a skipped tooth or a bent rack causes the room to bind.

Slide-out seals: bulb and wiper seals keep water out; a torn wiper seal lets water track in, and the seal must be replaced, not glued back in place.

Slide-out topper awnings protect the roof of the slide; they must be tensioned correctly or they flap and tear in wind.

Hydraulic leveling systems: check fluid level with jacks retracted, and use the manufacturer's manual retract procedure (often a valve release plus pump) if the panel fails.

Electric leveling jacks: the controller needs a level zero point set; a jack that runs but does not lift may have a sheared pin or a stripped gear.

Patio awning: the spring is under tension in the roller tube; releasing it without control causes injury, and the fabric must be replaced with the roller secured.

Leveling blocks and chocks: level the coach before extending slides so the room does not bind; never extend a slide on soft ground without support.

Slide-out roof and floor: check the floor for water damage and the roof for a torn topper after every trip; a slide that is out of alignment can leak at the flange.

Diagnostic order: verify the complaint, gather the customer's description (when, how often, conditions), inspect, test, then repair; do not replace parts to find the fault.

Intermittent faults: check grounds, connectors, and wire chafe first; a wiggle test and a voltage-drop test find most intermittent 12 V problems faster than parts swapping.

Warranty and authorization: get customer approval and a signed estimate before work beyond the diagnostic; document the cause and correction for warranty claims.

Customer handoff: explain what failed, what was done, and what to watch for; demonstrate the fix (slide operation, water heater bypass) so the customer can verify it.

Complaint vs cause vs correction: the complaint is the customer's words; the cause is the verified failure; the correction is the repair. All three belong on the work order.

Repair verification: test under load and in the condition the customer described (hot day for AC, full tank for water pump) before releasing the unit.

Parts selection: match OEM or equivalent ratings; a lower-rated fuse, a different LP orifice, or a mismatched sealant is a comeback waiting to happen.

Safety inspection on every visit: check LP leaks, CO and smoke alarms, tire date codes, and brake lights; a found defect should be reported even if not repaired today.

Comeback prevention: a repair that returns is often an incomplete diagnosis; re-interview the customer, re-test the system, and check for a second fault before replacing the first part again.