The problem with 158 air-con is that it's 158 air-con, it's just a lousy system that can't be made to work well for more than a few weeks. Refurbishing it won't fix it for long as it's simply not fit for purpose/badly designed. There's always some knocking around that work, but it really is pot luck, and if they've not been through the works for a few months, your luck's likely to be bad.
I've heard there is often one issue which isn't exactly of the air-con's making though. If it's playing up, some guards open the windows to help, leaving the air-con on, which I'm told is the worst thing to do, as the air-con thinks it's getting cold and starts pumping out HOT air! Right or wrong, I have to say since I was told I've noticed that opening the windows on a dodgy set does seem to only make things worse.