Red Seal RV Service Technician flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

LP specific gravity

Propane vapor is about 1.5 times as heavy as air, so it settles in low areas such as bilges and floor-level compartments. Leak detectors are mounted low, and ventilation must account for pooling.

Manometer test

A water-column gauge measures LP system pressure, typically 11 inches WC at the appliance manifold. With appliances off, the system must hold pressure for the timed test with no drop.

Two-stage regulator

A first-stage regulator at the cylinder reduces tank pressure to about 10 psi, and a second-stage regulator at the coach reduces it further to 11 inches water column for appliances.

Ohm's law and power

V = I × R and P = V × I. A 12 V device drawing 5 A has 2.4 ohms resistance and uses 60 W, which sizes fusing and wire gauge.

Voltage drop rule

Round-trip DC voltage drop equals 2 × length × current × conductor resistance. Keep total drop near 3 percent (about 0.36 V on 12 V) or motors and electronics operate poorly.

Battery state of charge

A rested flooded lead-acid battery reads about 12.6 V at 100 percent, 12.2 V at 50 percent, and 12.0 V at 25 percent. Discharging below 50 percent shortens life.

50 A shore service

A 50 A pedestal provides two 120 V legs, a neutral, and a ground, for up to 12,000 W total. A 50-to-30 A adapter feeds only one leg.

Series vs parallel batteries

Series connection adds voltage while amp-hour capacity stays the same. Parallel connection adds amp-hour capacity while voltage stays the same. Two 6 V batteries in series make 12 V.

Inverter continuous rating

The continuous watt rating must exceed the sum of AC loads running at once. The surge rating covers motor starting, and undersized DC input cable causes low-voltage shutdown.

Water pump short-cycling

A pump that cycles on and off rapidly usually has a waterlogged accumulator tank or a faulty pressure switch. A pump running continuously points to a leak or bad check valve.

Water heater anode rod

In steel tanks a magnesium anode corrodes instead of the tank lining. Replace it when about 75 percent consumed, or the tank will rust through.

Black and gray tank order

Dump the black tank first through the 3-inch valve, then the gray tank through 1.5-inch lines to rinse the hose. Use a dedicated hose for flushing only.

Air admittance valve

An AAV is a one-way vent that lets air into a drain line behind a P-trap without a roof vent. A gurgling drain often means the AAV is stuck shut.

City water check valve

A check valve at the city water inlet prevents backflow into the coach and keeps the fresh tank from filling when connected to city water. A failed valve causes the tank to overflow.

Air conditioner delta-T

Measure return and supply air temperature at the unit. A difference of roughly 15 to 20 Fahrenheit degrees (8 to 11 Celsius) indicates the unit is removing heat normally.

Furnace sail switch

A sail switch proves the blower is moving air before the gas valve opens and ignition occurs. A dirty blower wheel or blocked duct prevents it from closing.

Furnace lockout

After several failed ignition attempts the control board locks out and stops trying. Common causes are the igniter, gas pressure, sail switch, or a blocked burner.

Heat pump balance point

The outdoor temperature at which a heat pump can no longer meet the heating load. Below that point the gas furnace takes over, and the heat pump loses capacity gradually.

Lap sealant use

Self-leveling lap sealant is applied to horizontal roof seams and around vents. Non-sag sealant is used on vertical surfaces. The product must match the roof membrane material.

EPDM membrane

A synthetic rubber roof membrane. It is damaged by petroleum-based solvents and sealants, so only compatible cleaners and sealants may be used on it.

Delamination

Separation of the exterior skin from the substrate, shown by bubbles or a dull thud when tapped. It usually follows long-term water intrusion and weakens the wall structure.

Butyl tape vs sealant

Butyl tape forms a gasket behind frames and vents. Sealant covers fastener heads and edges. Both are needed, and one does not substitute for the other.

Tongue weight rule

For a conventional trailer, tongue weight should be about 10 to 15 percent of the loaded trailer weight and must not exceed the hitch or receiver rating.

GCWR vs GVWR

GCWR is the maximum combined weight of tow vehicle and trailer. GVWR is the maximum weight of one vehicle or trailer alone. Payload rating often limits the tow vehicle first.

Weight-distributing hitch

Spring bars transfer tongue weight to the trailer axle and the tow vehicle front axle. Setup is verified by measuring front fender height before and after hitching.

Tire DOT date code

The last four digits of the DOT code give week and year of manufacture, such as 3521 for week 35 of 2021. RV tires often age out in five to seven years.

Slide-out manual override

Each slide system has a documented manual retract method, such as releasing a hydraulic valve or using a crank on the motor. Know it before a failure traps the room out.

Slide-out topper awning

A small awning over the slide-out roof sheds debris and water. It must be tensioned correctly or it flaps, tears, and fails to protect the slide seals.

Hydraulic leveling fluid check

Check the reservoir level only with all jacks fully retracted. Fluid added with jacks extended will overflow when they retract. Use the manufacturer's specified fluid.

Complaint, cause, correction

The complaint is the customer's description, the cause is the verified failure, and the correction is the repair performed. All three belong on the work order for warranty.

Voltage drop test

Measure voltage across a loaded circuit or connection rather than at the battery. A drop across a ground or connector locates high resistance faster than parts replacement.

Comeback diagnosis

A repair that returns usually means an incomplete diagnosis. Re-interview the customer, re-test under the original conditions, and look for a second fault before replacing the first part again.