RV connected 2 external AC-check light on dometic refer comes on when RV batteries r low. I thought refer automatically operates on AC when connected to external AC and don't understand check light.

You don't say what type of RV you have, so my answer is generic. Most RVs have two battery systems, "house battery" for living amenities (fridge, interior lights, furnace, water pump, etc.) and a second "chassis battery" for driving functions (engine start, exterior lights, wipers, etc.) Ground connections are generally the same, the positive terminal is never cross-connected between the two battery systems except when a charging voltage is detected.

Lights are 12V nothing to do with 120 V AC circuit. Check batteries and inverter

If your battery is getting hot, there's a chance it may be needing to get replaced. If you wait too long, the case can crack and leak battery acid. Worst case scenario, it can explode causing more issues and damage. Remove the battery and take it to a local auto parts store to get checked. If it is bad, you already have the battery there to get an exact size and style needed without having to worry about the core charge.

The RV fridge with get power either by: 1. 120VAC power plug or 2. 12VDC with propane. Some modes will have an automatic switch of AC power goes out. Make sure you keep propane on hand as well.

The most common problem is blown main fuses on the power unit which blow when you operate or try to operate the slides with low batteries and the power supply not connected to the landline power source.

Like mentioned, I would check that the charging system is working. You said "Batteries", so I assume the RV has a diesel and there are two batteries.... Assuming the engine cranks okay, the charging system is operating properly.... I would check the connections and cables that feed power to the jacks. May well be loose connections, frayed cable or something that is hindering the flow of power to the jack motors.

Try these places

http://www.rvpartsnation.com/rv-heating-cooling/rv-air-conditioner/dometic-air-conditioner/dometic-air-conditioner-parts/dometic-quick-cool-ducted-return-air-grill/?gclid=CLn8rMiR0M8CFYgvgQodw_kKOg

http://www.adventurerv.net/dometic-air-conditioner-return-air-grille-center-duct-p-28803.html?gclid=CKSnz_yR0M8CFY4vgQodnAgNrQ&utm_campaign=partsfeed_ppc&utm_medium=cpc&utm_source=Froogle

120-
VOLT
AC
SYSTEM
The following electrical components (if so equipped) will only operate when your
RV is connected to shore power: 120 to
12-volt power converter, air conditioner,
120-volt refrigerator, microwave oven, television(s), fireplace and appliances
plugged into convenience receptacles.

SECTION 6 - ELECTRICAL SYSTEM JAYCO TOWABLE
6-2
120-
VOLT
CIRCUIT
BREAKERS
The 120-volt AC circuit breakers located in
side the main load center protect all
120-volt wiring and components in the RV fr
om circuit overloads and short circuits.
Should a circuit overload or short circui
t occur the circuit breaker protecting the
affected circuit will "trip" preventing the flow of electricity through that circuit.
If a circuit breaker trips, shut "off"
the appliance on that circuit (i.e., power
converter etc.) and allow the circuit breaker to cool down for a brief period of time.
After the cooling down period, reset the circuit breaker by moving its lever "off" and
then back to the "on" position. If the circuit breaker re-trips or frequently trips,
contact your dealer to have the electrical problem diagnosed and repaired.
A circuit breaker identification label is permanently attached to the inside surface
of the 120-volt load center.
Maintenance and Replacement
At the beginning of camping season, inspect the circuit breakers and replace as
needed. Test by turning each circuit breaker "off" and back "on". Circuit breakers
are wearable parts and must be replaced
as needed, as part of your RV
maintenance. If you have any questions, consult your dealer.
Please contact your dealer for repair assistance when replacing circuit breakers.
CONVERTER
The power converter converts 120-volt AC power to useable 12-volt DC power
when the shore power cord is connected to an external power source.
The converter has a built-in protective thermal breaker that will shut it down should
overheating occur. Overheating can be
caused by operating the converter above
its maximum power output for an extended period of time, or by an obstruction to
its ventilation air flow. To reduce converter heat build keep unnecessary 12-volt
lights and motors turned "off"
.
Keep the converter cooling fins and fan clear of
obstructions.
Inspection and maintenance
If the 12-volt power converter is not working (auxiliary battery not being charged)
check the reverse polarity fuse(s) in the converter fuse panel.
There are no
customer serviceable parts inside the converter case and the
manufacturer's warranty will be void if
the case has been removed
. If you
have further concerns contact your dealer.

i am asssuming that you are talking about your coach battery bank.are they 12 volt or 6 volt battery system. the arc is a short. check polarity. can you charge the batteries with an external battery charger? if so. then need to check converter output from your mian power panel. there are a few other things to check. need more specifics. and you need to have a volt meter handy.

First, turn off AC, refrigerator, all lights, water heater, and pump.

any of those will draw current and make sparks when connecting the terminal on the battery.

check the amount of current draw with an ampmeter.

use an ohmmeter to check the wire to ground - without connecting the battery to see if there really is a dead short to ground.

If you don't really understand above, then: get to a RV repair place that is familiar with winnebago older models.

good luck.

there is a sort some were and it will need to be rectified before it over heats or catches fire.check wiring without the battery on with a meter. turn every thing off and test lines then turn one thing on test then turn on something else keep doing this on all electrical equipment till you find the unit at fault.