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1994 940t Air conditioning questions

posted by  Amarin on  Fri Jun 3 20:08 CST 2016
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last visit: Thu Oct 23 22:42 CST 2014
[RELATED]

Hi,

Car 1:
The orifice tube (OT) is partially blocked. At no time should the lines frost even in any low refrigerant condition. The OT must be replaced which include evacuating refrigerant, dismantle OT line, putting in new OT, button all up, vacuum down and weigh new refrigerant in. Even if cooling is still adequate we're talking about compressor lubrication. Partially blocked OT may still let some refrigerant thru but would reduce oil going to compressor. Long term use in current condition may cause compressor damage.

A complete service would include flushing the condenser of any internal debris or replacing the condenser if flushing didn't help. A more practical service would be just to replace the OT for the time being and when frosting happens again in the future replace the OT again. Hopefully any internal debris would slowly make their way out and filtered by the OT.

Car 2:
The refrigerant is low. Thus causing rapid compressor cycling. You may just top it up using the rapid dispenser but questions remains. How much to top it up? What is causing the leak? Where is the leak? To answer these you may firstly top it up then practically apply soap bubbles to ALL joints to find the leak. If leak doesn't appear then it could be due to normal rate of refrigerant seeping out of all rubber parts in every 3 to 5 years. If leak appears then repair is needed. Repair may include replacing O rings and rubber hoses. Rubber hoses may also leak at their crimped connections due to long term vibration and heat.

So how much to top it up?

Ideally the system should be evacuated, vacuumed and proper refrigerant weighed in. If no oily residue seen at any joints and rubber hoses then you could add a bit more of refrigerant oil about 10ml to 15ml during recharging to compensate for loss during evacuation.

For practical purpose just top it up until no compressor cycling, cooling is adequate, the gauge reads between 35psi to 45psi according to ambient temp AND the inlet/outlet evaporator lines have about the same coldness. R134a pressure vs ambient temp chart is available on the net.

Hope this helps,
Amarin.





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