Class 158 air-con
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This extract is copied over from a reply on another thread; it is undoubtably the most informed and thorough answer to the perpetual question of why is Class 158 air-con always crap I thought it was well worth sharing as others on this thread have asked this question many a time.
[If the poster from the other forum objects please post it here and I (or the mods!) will immediately edit this thread and remove. Thanks].
The 158s have three systems fitted; Temperature (formerly part of Westinghouse, but now all parts are overhauled by Pullmans AC of Durham), Ebac & Liebherr.
The Temperature is the as-built system, and is a large capacity split system, with the hydrostatically powered Condenser/Compressor module underframe and two Evaporator/Heat exchanger modules in the roof spaces above each vestibule. The refrigerant ('gas') it originally used was made illegal, so the systems were unable to be used for a while, but most have now been converted to R134A type refrigerant so are usable again.
The Liebherr is the retro-fitted system, and consists of two self-contained cooling/heating roof modules, one per vestibule and an underframe mounted 'wedge' module containing 3-phase alternator providing power to the roof modules.
Both systems are controlled from a 'Mircopac' control unit, located in the SMS bulkhead cupboard in the #1 vestibule, which takes all the vehicle and sensor inputs to controls the system, using the bank of relays/contactors below the Micropac.
The Ebac system is a modified Temperature system, with reliability modifications to the underframe module and evaporator fans/duct work, along with a different, more user-friendly ACCU (Air Conditioning Control Unit) made by Ebac.
For both the Temperature & Liebherr systems under normal 'in traffic' conditions, the Micropac defaults to Auto, which is designed to automatically maintain the ambient temperature within the saloon to 21 degrees, by using cooling/heating blending aswell as venting. The Ebac systems micro controller unit also does this.
The differance between the Temperature/Ebac and the Liebherr systems is that the Temperature system is very large split system that contains alot of refrigerant ('gas') and has a lot of pipework and connections, so there is huge potential for leaks, meaning refrigerant can be easily lost. Whilst the system when it works is very efficient and can cool the saloon in a very short space of time, its other main vulnerability is that due to its nature, the system must pump down before the engine is shut down or else liquid refrigerant can be trapped in the system, which hydraulic locks and thus damages the Compressor when it is next started up. The 158s have an interlock where by when the cab engine STOP button is pressed (or the desk has been keyed out for 15mins), the engine is prevented from shutting down, and the A/C system will immediately begin to pump down if required and once this is completed, it will then allow the engine to shut down. This can be bypassed by pressing and holding the cab STOP button for
more than 5 secs or so, or by pressing the local STOP buttons on the underframe.or by the operation of the Fire test button. The engine will also immediately shut down in the event of low oil pressure,low coolant & loss of fire system integrity, in which case the A/C system reliability is scarified for safety purposes.
I cannot emphasise enough how important it is that the A/C system is allowed to pump down prior to shut down to ensure it does not get damaged unless in an emergency, and whilst most drivers are aware of this and when leaving a unit, press STOP once then key out and let the unit shut down in its own time, i all to often witness drivers, especially on depot, pressing and holding the STOP button while the A/C is still running in cooling. Literally one or two shut downs carried out without pumping down can destroy the compressor and render the system useless!!
I have scalded several drivers in the past who mindlessly hold the STOP button when bringing units in from service or moving spare units around the depot, it is just plain laziness. I am not sure if drivers are still trained on this point when learning/refreshing 158s as traction, but please drivers take this on board if you drive 158s/159s!!!
The Liebherr system has self-contained modules, which carry much less refrigerant all in the roof space and are powered by the 3-phase alternator which takes the place of the original underframe module. This make them much more reliable, as long as the alternator is functioning correctly, but even this system must be allowed to pump down before engine shutdown, but the time taken is considerably shorter.
The fundamental vulnerability of all system is that the Compressor/Condenser fan on the Temperature/Ebac systems and the alternator or the Liebherr system are all powered by the common Hydrostatic system that also powers the Radiator fan & main alternator, so if the 'serck' fluid is lost through a leak or hose failure or the main hydraulic VD pump fails, no power is available to either of the systems.
Resetting the system using the 'RESET' button generally does nothing and clearing the fault codes has no effect on the operation of the system, it meerly erases the stored record of High/low pressure faults, meaning that maintenance staff cannot recall the faults to see what had occurred in traffic.
All systems will default to Auto, even after being powered on/off via the ACIS (A/C isolation switch or by operating the ACCB (A/C Circuit Breaker) on the cab bulkhead behind the driver. The system will always try to regulate no matter what, and the only thing that will upset it is if the Micropac itself is faulty (very rare) or one of its 4 temperature sensors, E1 (Evap 1), E2 (Evap 2), AA (Ambient Air) or SS (Supply Sensor) is faulty and reading high/low, and in these circumstances the system gets confused and will try to heat (or even cool) when it is not required, hence making things uncomfortable and overworking itself, often causing more damage. If the system has low no refrigerant, it will still ask for cooling, but will often immediately trip out on Low Pressure and rest, then try again. The best thing to do in this case is isolate the system using the ACIS and open the hopper windows, as otherwise the system will just constantly fight itself.
On FGW west fleet, we have a mixture of Liebherr and Temperature systems (Plus 158798 with Ebac) and we had a campaign this summer to get maximum possible availability. So far, we are so far achieving a pretty good percentage (about 75% when I last checked), minus the unavoidable in-traffic failures and we also have a few vehicles with systems that require major/long-term repairs which are being planned in and stopped when fleet availability permits (ie. after the summer timetable! - crazy i know, but unfortunately our fleet just isnt big enough.....)
We have found that often train crew who believe they are helping actually hinder and cause more problems (as in a post above, where 'resetting' the system literally achieves nothing whatsoever!!!!). We have also seen cases of vandalism, where the Micropac keypads and displays have been 'T-Keyed' or wiring connectors/plugs dislodged/detached, which we assume is only carried out by certain train crew for reasons unbeknown to any of us.
To combat this, as the 158 feet goes through a Reliability Modification program, we are fitting locks to the SMS cupboard that only maintenance staff have keys to and a viewing panel is being cut into the cupboard door to allow train crew to view the Micropac display and see what the current temperature is and what the A/C is currently doing (Vent/Heating/Preheating/Cooling 1/2/3/ etc.) and any A/C isolations that are required will be carried out by maintenance staff or RSIs/Mob Techs.
Hope this explains things a bit, sorry its abit long-winded, but there is no real simple explanation to your question!!
Regards to all, BW.
