RWD - A/C Universal Compressor Oil and Leak Detection

Volvo RWD 900 Forum

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A/C Universal Compressor Oil and Leak Detection 900 1995

Dear jd620,

I think you plan to find the leak using dyed compressor oil. A good plan however if oil added too much you could disrupt the system oil balance i.e existing oil plus newly added oil. Cooling (i.e heat transfer) would be affected with too much oil in the system. The extra oil would much coat the insides of the evaporator/condenser tubes hindering heat transfer. The SAFER way is to use R134a with added dye.

The Behr oil is of PAO variety with a viscosity of 68. Your Seiko-Seiki compressor needs oil with viscosity of 100. Recommended Volvo oil is #1161426 which is a PAG100 (i.e viscosity 100). PAG and PAO oils are both of synthetic variety but traditionally PAG oil is used in automobile AC system. PAO is more suitable for use in other refrigeration system (i.e industrial freezer). The debate why PAG is much more suited to cars could be read from the web if you're much inclined but in the end PAG wins.

Lets concentrate on finding the leak. The CCOT system in our 940/960 cars have resting pressure of 90 to 110 PSI (ambient temp dependant, engine OFF) and working pressure of 35 to 45PSI at low (evaporator) side, 160 to 250 PSI at high (compressor-condenser) side. Thus your 25PSI plan to find leak using soap bubbles would appear pale in comparison.

How to go about it?
With big leaks, refrigeration oil would be spewed out from the leaking site at such above pressures. Look for oily site all along the hoses/compressor/condenser. Its unavoidable to open the HVAC enclosure to look for leak at evaporator but you could do this later. Find oily leak at engine compartment side first. Run your finger at the oily site to confirm its really oil (should be mixed with dust n dirt too).

From my experience such big leaks (which you can't vacuum down the system) could be at:

1) Crimped rubber hose ends (i.e compressor hoses) - the hose end becomes loose and OILY - find another good crimped end to compare tightness. Must replace entire hose end to end.

2) Compressor shaft seal - located hidden inside the pulley - your compressor clutch plate is OILY - this is a well known issue for the Seiko-Seiki compressor. Repair compressor or replace with another make (Zexel, Seltec, Sanden etc)

3) Leaking pressure switch (i.e. pressostat) - this especially the VIOLET and BROWN pressostat. I don't know why the GREY pressostat rarely leaks. But if this happens you MUST check your orifice tube (OT). This happens when the OT is blocked with debris thus the refrigerant back pressured to the pressostats. Must replace OT and the affected pressostat.

4) Leaking condenser coil from road rocks - this should be obvious as the high pressure leak would spray oil onto the inner side of front grille. Replace condenser.

Small leaks - which you could refill/recharge the system but emptied about a few days to a week later usually comes from the O rings. Any O rings on the system. Finding these leak would be better to use dyed refrigerant.

If no oily site found at engine side only then you should suspect the evaporator. IME the evaporator is rarely affected.

Hope these helps,


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New 1 A/C Universal Compressor Oil and Leak Detection [900][1995]
posted by  jd620  on Tue May 9 19:01 CST 2017 >

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