No heat coming from air conditioner - outside unit not working either. Only blowing cold air. "Sun" symbol not showing on remote but all other symbols are showing..

Make sure the setting on the remote is correct . Sun symbol for heating. Make sure the filters are clean. On heating, the indoor unit will 1/2 open the flap but the fan shouldn't start. The outdoor unit should start and if working properly, will be blowing cold air. The indoor unit will open the flap fully and the indoor fan will start once it gets hot then you should feel warm air. If the outdoor unit is blowing warmish air, I would say the reversing valve coil has failed or one of the indoor temp or pipe sensors are faulty. If a sensor fails, a "CH" error should appear on the display.

Press the 'mode' button on your remote until it says 'cool' or shows a snowflake symbol. Careful that you don't set it to 'heat' mode accidentally if it only has symbols. The 'sun' (heat) mode symbol can look like a snowflake on some of these remotes. Then set the temperature to suit you.

Symbols:
1. fan leaves - Fan only
2. Rain drop- Dry mode
3. Snow flake-Cool mode
4. Sun- Heat
5. A or AU- Auto mode.

Check wiring done correctly.
Symbolsin remote: To get proper cold air set temp 23 degree and mode"cool". To get heat set temp 30 degree and mode in "Heat"
Now symbols:
1. fan leaves - Fan only
2. Rain drop- Dry mode
3. Snow flake-Cool mode
4. Sun- Heat
5. A or AU- Auto mode.
Helpful?

To get cold air set temp 23 degree and mode "cool".
Now symbols:
1. fan leaves - Fan only
2. Rain drop- Dry mode
3. Snow flake-Cool mode
4. Sun- Heat
5. A or AU- Auto mode.

does it cool ? when on cooling which would be a snow flake symbol. if it does not heat or cool you have other issues whens the last time it worked

Sounds like compressor not running. may be a bad capacitor, could also be low on freon.

My Mistral was working yesterday (on heat) now it won't. Just sits there as if warming up but actually blows out freezing air - on "sun" mode.

If your unit is blowing heat inside and it's not a heat pump. It will be most likely electric heat in your case.
Sounds like you have a split unit meaning the condenser is outside and the cooling and the heat features are inside or under your home.If your Rudd is a heat-pump the outside unit will cycle/blow cold air outside in winter and hot air will cycle/blow outside during the summer season. Now, if for some reason the heat  is not coming on inside the house, would be the only reason that you would need to be concerned. Being a heat relay or breaker of could cause that problem. Hope this helps you, Sea Breeze