I am no mechanic and do not have any mechanic knowledge etc and would like to hear from experts here regarding an issue.

My query ...

On a Mercedes CL500 (2002 model) the water pump, idler pulley & tensioner was replaced by a garage. The car was taken by the car owner after the repair works and was driven around. The following day, according to the car owner, after driving around, the car had to be recovered and was taken to another garage. Also, the check engine light was 'on'. The second garage upon inspection gave the following explanation to the car owner:

Upon inspection they found a poorly fitted water pump and so due to this the check engine light was on, whilst at the same time this restricted engine performance.

Due to the poorly fitted and damaged water pump components the vehicles air conditioning had three times more pressure than required and therefore they had to do some repair work on the AC side of things.

They further explained that the water pump plays an integral role in the fully functioning of the entire engine system pumping water the to the coolant radiator as well as assisting the air conditioning.

So my first question to experts here is that can a failed/poorly fitted water pump affect the AC system and as the second garage explained - make the AC system work under three times more pressure than usual?

What are the possible things that could happen due to a poorly fitted water pump and related components (i.e. idler pulley & tensioner)?

  • the first that did the repair work did, according to them, do all necessary post work checks, also left the engine running for a while, taken for test drive and was fine before releasing the to the car owner
  • No mention of what the check engine code(s) were
  • No mention of coolant sign being on
  • Bare in mind that the driver was able to drive car until the following day
  • No explanation given why the car was recovered, or whether it was 'driveable' but still recovered
  • there is mention of the coolant temperature display sensor being replaced by the second garage but that was 2 weeks after the AC related repair works were carried out by the second garage

Your input will be much appreciated.

  • 1
    I would like to know what the "check engine light" codes were. The light is normally for emissions related issues and typically wouldn't come on if the car was just overheating, etc.
    – JPhi1618
    Commented Apr 26, 2016 at 18:52
  • I've updated the original query with more info. Hope that helps.
    – jangz
    Commented Apr 26, 2016 at 19:09
  • 1
    Engine cooling system has nothing to do with AC.
    – Moab
    Commented Apr 27, 2016 at 0:05

1 Answer 1


The only relation that the water pump might have with the AC is that in some cars they are linked with the same belt and that's all...

The only way that you could make the AC develop more pressure than the normal, is by either fitting wrong belt or fitting wrong pulleys to wrong pumps.

If they fit the water pump wrong chances are that the car was leaking coolant. If it was leaking slow enough to be unnoticed after the test drive but big enough to run out of coolant the next day, then it is possible that the car overheated and had to be recovered.

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