air con still does'nt work

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The fans on the V8 are controlled by two things
a) a pressure switch which detects high pressure in the system (High pressure=high refrigerant temperature) and an output from the engine ECU when the engine coolant temperature rises to a very high level, thus assisting the viscous fan in lowering the coolant temperature. The aircon system is unlike most systems, as it is a computer (HEVAC) controlled system. It is a misbelief that the condenser fans should be running to make the aircon work but it's the condenser itself which basically cools the refrigerant, if it's unable to do so, the pressure rises in the system and the fans come on to assist cooling.
Furthermore, the condenser which is virtually the same size as the engine radiator is located directly in front of it and air drawn through the grille by the engine fan passes firstly through the condenser and dissapates most of the heat. That is why the fans do not cut in as often as you think they should. When the car is moving, obviously, cool outside air is forced at a greater rate through the condenser. Probably, the only time they would come on is if the car was stationary on a very hot day or if the fins were blocked with dead flies etc., in which case I would have thought that the engine temperature would also rise as the radiator would also be starved of cooling air flow.
It is good practice to remove the grille once or twice a year and pressure wash through the condenser (No need to remove it) fins to remove any build up of rubbish etc.
 
Irishrover said:
The fans on the V8 are controlled by two things
a) a pressure switch which detects high pressure in the system (High pressure=high refrigerant temperature) and an output from the engine ECU when the engine coolant temperature rises to a very high level, thus assisting the viscous fan in lowering the coolant temperature. The aircon system is unlike most systems, as it is a computer (HEVAC) controlled system. It is a misbelief that the condenser fans should be running to make the aircon work but it's the condenser itself which basically cools the refrigerant, if it's unable to do so, the pressure rises in the system and the fans come on to assist cooling.
Furthermore, the condenser which is virtually the same size as the engine radiator is located directly in front of it and air drawn through the grille by the engine fan passes firstly through the condenser and dissapates most of the heat. That is why the fans do not cut in as often as you think they should. When the car is moving, obviously, cool outside air is forced at a greater rate through the condenser. Probably, the only time they would come on is if the car was stationary on a very hot day or if the fins were blocked with dead flies etc., in which case I would have thought that the engine temperature would also rise as the radiator would also be starved of cooling air flow.
It is good practice to remove the grille once or twice a year and pressure wash through the condenser (No need to remove it) fins to remove any build up of rubbish etc.
Click to expand...

That's probably why my condensors have needed changing so often - most cars don't need dismantling and washing of condensors, but hey, this is a P38 !!!!:doh::doh:Will try to remember to do this from time to time!!!
 
I would just add to Irish's excellent explanation that there is a second pressure switch that switches the fans between half speed (fans connected in series) and full speed (fans connected in parallel) a totally unneccasary complication in my opinion.
 
I too am on my 3rd condenser.
Years ago, an Aircon Guru advised that the condensers should be pressure washed through twice a year.
A mate of mine has a 1994 Nissan with aircon and he's never had a drop of refrigerant put in it and it gets feezing inside. Had the gas level checked last year and it's still okay!!
 
One thing's for certain, he's spent less money and time fixing it than I have with the P38. No suspension, overheating or blend motor problems either. Services it twice a year and no oil or water in it between services.
That's why he's always got more beer money than me!!
 
Does anybody know what pressure the a/c system should be?
I had noticed that the a/c wasnt working after a new condensor and regas about 6months ago, as the clutch wasnt kicking in I thought it was be a pressure loss. So thnking of the wallet I thought I'd try the Halfords tin of refrigerant. But with the engine running the pressure was over 100psi (probably 150psi), well over the 25 to 45 that the gauge on their tin said was normal.
So now (I think) I know its not a leak, but that pressure seems high considering what that halfords gauge says.
Any thoughts guys
thanks
 
I thought the large diameter pipe was the low pressure side? Pressure varies hugely with temperature. My book say's with the system cold, engine idling and full cool selected the pressure should be around 45 to 50 psi on the low pressure side. When the system condensor is very hot, ie the air con has been running for some time, the pressure on mine reads ove 300 psi
 
By the way..do not try reading the pressure from the high pressure side unless you have a gauge & hose capable of taking in excess of at least 500psi. Furthermore, accidental spillage etc. can easily cause severe freeze burns.
However the"Gas in a can" top up kit test gauge will give you a rough idea and only use it as intended...on the low pressure connection only.
 
The minimum pressure for the compressor to kick in is 17 psi according to the spec. therefore it should work. Disconnect the round plug at the compressor, Set the temp. to "LO" and start the engine and check for 12V accross the two pins at the socket. If you have 12V, reconnect the plug and pierce the two leads going to the clutch coil which is located inside the pulley and check for 12V there. If there is no voltage, there is a thermal fuse located on the top of the compressor towards the rear..probably, that has packed up. If you are getting 12V at the clutch coil leads, either the coil has burnt out or the electro magnetic clutch plate has stuck or the air gap is too large, should be around .015-.020". There is a shim washer behind the clutch plate which can be removed/reduced if needs be.
Suggest you do the electrical checks first and let us know the outcome before moving on.
 
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