air force 17000 but split unit (B+Q special) not playing the game all the time.

[aircon newbie]

Hi guys,
New to the forum and looking for a bit of guidance. I have one of the above systems (KFR-45GW/NJ16). It is about 7 years old and has performed faultlessly since installation. I know I should be overjoyed by this fact, based on some of the items I have found on here lol. But I lately it has started to play up a little.
I would appreciate any thoughts on diagnosing possible faults with the following symptoms.

When heating, it runs for 15/20 mins then just blows ambient air. It raises the room temp from 10 to 19 C, but the controller is set at Max(28 C). I have noticed that when it stops heating it appears to start heating the outside unit, as rain water produces steam from the outside fins. Both inside and outside unit fans still work, but only ambient, if not slightly chilled air is blown from the inside unit. It does not appear to reset it's self either. But if I turn it off and on again after a while it starts to work properly again for 10/20 mins.
Could this just be a gas issue, or is it likely to be something more serious. I appreciate that by spending £100 or so to get it re gassed I might by throwing good money after bad, but I would just like it to live on borrowed time for 12 months or so. I will then get it replaced with a proper setup.
Cheers

[install monkey]

defrost!- when its cold outside, the outdoor coil will freeze up- then it will stop heating to defrost the outdoor coil, then it should revertback to heating after 5/10 mins

[aircon newbie]

Thanks for your speedy response. That would make sense, but it is not that cold outside at the moment, and I have run the system with snow on the ground and not noticed this behaviour before. Might there be a fault that causes defrost when not really needed?
Thanks again for your input.

[aircon newbie]

Would a low gas situation cause early icing of the outside coil?

[Road_Runner]

Does the internal unit flash or show a numerical error code.?

[aircon newbie]

Yeah, have found an online service guide. They are a gree unit by all accounts. Had a visit from local air con guy who decided it was poss a bit low on gas, as it enters auto defrost cycle, but cannot get out of it. So slightly low gas was suspected. Might also be a temp sensor, but long shot. Unable to add gas, no service ports. For complete solution advised remove self sealing couplings, plumb properly and regass. Cost makes it uneconomical to repair. Advised to treat it gently so as not to get it into auto defrost. It works OK otherwise, reaches 18 degrees then cuts out, and in again as you would expect. Just unable to recover from auto defrost without pulling the plug and re setting it. Unless anyone knows better lol