I have a 1990 TIOGA by Fleetwood with a S620 Silhouette by dometic.my problem is that it works fine on elictric but not on gas. i can see that the flame comes on but it does not refridgerate

Hi, The cooling circuit of your refrigerator depends on a small section which must be kept hot in order to heat up the ammonia in the tubing. It can be heated by a gas flame or by an electric resistance heater if so equipped. Usually these two systems are completely separate. It sounds as though service is needed for the gas burner portion. The usual causes are the burner orifice being plugged or damaged, or the gas control being plugged or needing adjustment. Plugged burner tips can be cleaned out with solvent and compressed air, and replacement burner tips are available from small appliance parts distributors. Make sure the thermocouple flame sensor is in the flame path per the manual, and that all the fittings are tight. The thermocouple compresses the air in the tubing as it is heated, opening a valve in the gas control it connects to. If there is any air leakage, the valve will not open. Make sure the flame height and color is adjusted per the manual, and that the vents are free and clear of blockage. Also, make sure that there is LPG pressure at the control valve. 

Thanks! Sandy

Itys the common problem of gas inlet valve blocked that has to be replaced.as you see the flame because the gas outlet valve is proper .but inlet valve is blocked so its not working on gas mode.
get the inlet valve replaced. keep updated.thank you for using fixya.please do rate the solution.thanks.