PeachParts Mercedes-Benz Forum - View Single Post - W108 - 1972 280SE 4.5

Tomguy · #6 03-10-2015, 01:16 PM

Jose,
How did you check the freon level? If the compressor is running you cannot get an accurate pressure reading from a gauge. Having pressure in the system isn't enough to know. You really do need gauges to do anything A/C related (trust me here! Others will say the same thing. Even the cheapo set I got from Harbor Freight for $40 has proven essential in setting pressures right on both my Jeep I converted to R134a and my 300M that I have replaced the compressor & evaporator on).

Does the compressor kick on at all? If not, you can't really check the pressures anyway. Sure, you can see what the static pressure is, but it won't give an accurate representation of the proper high/low side values, unless someone else with a w108/109/111/112 with the same A/C system would give you their static reading to compare to. While the system may seem complex, it's essential to know the basics and once you do, it's easy to troubleshoot:

Compressor compresses freon to the high side (condenser).
Expansion valve/tube to bottleneck pressure (so high side stays high and low stays low).
Evaporator (low pressure).
Accumulator/Dryer (removes moisture from system).
Back to compressor.

If the expansion valve is clogged, the high side will be too high and low side too low, so the freon won't flow between the two sides. As a result, the evaporator can't remove heat to transfer it to the condenser.

If there is not enough freon, the high side won't get high enough and the heat won't be able to be dumped from the system at the condenser. Obviously, any leaks can cause this.

If there are no leaks, your evaporator is likely fine. It's unlikely to become clogged unless you have another issue, like a dying compressor spitting metal into it, and even then the expansion valve is more likely to become plugged/stuck before the evaporator goes bad.

The condenser is the high-side part. If your high side pressure is too high, it may blow out. A bump, or piece of road debris (like a rock) can also pop the condenser. It can also become clogged (especially during love-bug season in FL) and lose efficiency.

Without pressure readings though, everything else is just a guess. If you do need to put freon in, I'd suggest using the kind with UV dye, so you can find your leaks.