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how to add freon to a 1990 Red Dot R9720-1

You can’t buy it anymore. It’s illegal in the USA From 2015, it will be illegal to use Hydrochlorofluorocarbons (HCFCs), including the ozone-depleting refrigerant gas R22, in refrigeration, heat pump and air conditioning (AC) systems. R22 is commonly used in AC systems pre-dating 2004 and so its ban will have a major effect on air-conditioning costs. All new air conditioners and heat pumps use R-410A, the more “environmentally sound” refrigerant. R-22 is still the most commonly used refrigerant in existing air conditioning equipment in residential homes today. However, per the Montreal Protocol, caps have been established to eliminate the production of R-22.

Often when you need to recharge a cooling system you have a leak in the lines or condenser coils. Do a full inspection of the lines using a marker within the coolant (refrigerant) and black light to locate the leak. Once you have resolved the leak/s then you can recharge the system. Depending on your country you maybe limited on what refrigerant you can use. Make sure you comply with local govement regulations. As far as recharging you’ll need a gage set and you may need a compressor as well. Lastly, a tank of refrigerant and you may need a second empty tank to remove the old refrigerant to fix the lines. Here is a copy of the Red Dot Service Training Manual: Service Training Manual As there are so many versions of the unit it’s best to contact Red Dot directly to get the needed manual and details on what refrigerant you can use for your exact unit. Here is their contact page: Red Dot Corp.