Well, I did say that I wouldn't moan about the air conditioning failures after getting my free ice cream today, BUT, something doesn't seem quite right. There have been many complaints on Twitter this week concerning the problem and it's made me think; I have made 11 journeys on FGW▸ Class 158 trains this week, and the air conditioning was only working on one of them (the 1840 from Salisbury today on which I travelled to Westbury). I have also made 8 journeys on SWT▸ Class 159 trains in the same period and the aircon was working on all of them. There is also obviously a similar problem on the HSTs▸ , from reading the tweets. Do the different operators have different priorities?
The FGW 158s are intensively used compared to the SWT 159s so yes, there are different priorities albeit forced onto FGW and that is to keep as many trains in service as possible.
There's also three different types of air con fitted to the 158s known Temperature, Ebac or Liebherr. The FGW fleet is a mixture of Temperature and Liebherr. There are drawbacks to each system, Temperature for example uses extensive amount of pipe work and connections which increases the risks of leaks and ultimately a loss of refrigerant.
HSTs again comes down to ensuring maximum availability of carriages although I believe its only Laira depot that handles major work to the air con units
The problem with the HST air con units is their design. Due to the age they exhaust hot air out underneath the carriage (whereas more modern stock exhausts hot air through the roof of the train). Therefore, when the train sits in a platform with little air flow underneath the train the air con units basically start running hot and eventually trip out to prevent damage. This can only be reset at a maintenance depot. The air con units are modular but obviously they can only be removed if there's a replacement to go back in.
Turbos, air con modules are still under warranty. They were fitted under an 'install and maintain' contract. There were "issues" raised last under regards the "maintain" part of that contract (or so we heard). Modifications were made over the winter to these units which included replacing evap and condenser units as well as trying to increase air flow. They already take a considerable amount of power off the engine but it's not powerful enough to overcome and cool an overcrowded vehicle.