The A/C on my 1983 300d was not blowing cold enough so I took it to a shop for inspection. They said my compressor went bad. Had them replace compressor, dryer, expansion valve, flush, evacuate and recharge with the same type of refrigerant(134). Still not blowing cold enough, I've got 46F out the vents on the highway but 60F out the vents at idle on a 85F day? I've noticed that while driving with about 2500rpm, the temp out the vents will drop suddenly to as low as 42F, but then rise quickly to 46F and seems to "cycle" like this though spending most of its time at 46F. If it would stay at 42F it would be fine. Also, it seems that when set to max cool it runs warmer than when set to some other temp? Any ideas?

First, was it cooling about the same as it is now before the compressor "went bad" and was replaced?

If so, I'd say the shop ripped you off. It's more likely the pressure switch is bad. It sounds as if maybe as soon as the pressure gets high enough to cool good, it's cutting out.

__________________
Brian

_________________________________
Sometimes the only choices you have left are bad ones.
Agent Broyles (Fringe)

This is unbelievable!

I took it back to the shop. The service manager calls me and says, "who charged this thing? It's way overcharged." I remind him that they were the ones to perform the service. Looks like I chose a great shop! So, assuming the system works well now my question is what, if any damage could be done by an overcharged system?

when you say it was not cooling enough, do you mean it was cooling some, but a bit warm? if so, when they changed your compressor, it was probably not needed. also, 134 is not the correct refrigerant. if they weighed in the charge based on R12 specs, it is about 20% overcharged. how are they determining it is "way overcharged"? this sounds like a shyster shop to me. only way to know if it is overcharged is to remove the refrigerant and weigh the amount pulled out.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

As was said, you want about 20% less r-134 than R-12, so if they filled it by the weight on the sticker on the front, they overcharged it. This is probably what happened, and they can get it right using gauges.
You will have no damage from having it overcharged like that, unless it caused a leak (which it probably didn't). Even overcharged, you are still within MB specs, you just will shorten the life of the compressor if you run it like that long term.

To me, the charging mistake seems to be an honest fluke from a shop that isn't used to dealing with older cars.

The compressor though is a different matter. If it was cooling before to about where it is now, the compressor was fine. If it was cooling but getting under a 20* difference from outside air, the compressor had a reed valve or something out, and they were right in replacing it.

__________________
1984 300DT turbo 138k mi

Still hauling me to school and back.

Handy Site:
http://www.dieselgiant.com/

I initially took it into the shop because the old compressor was making a strange sound that I could only hear at idle and it wasn't cooling much at all. Shortly after getting the car back I took it on a long highway trip and noticed the poor performance of the a/c, it was significantly better than before though. I also noticed that the new compressor began making the exact same sound as the old compressor. took it back to the shop and that's when they told me the sound and poor a/c performance were due to an overcharged system and a loose belt. We'll see how well it works when I pick the car up today. I'm just concerned that I either didn't really need a new compressor or that the new one may have somehow been damaged from running it overcharged.

The total cost for compressor, dryer, expansion valve, temp switch, evac and fill was $900. Not a bad price at all, but I don't want to have to do it again any time soon!

It also concerns me that they overcharged it in the first place. Also, I had to talk them into replacing the expansion valve. They initially didn't think it needed one. Oh well, live and learn?!

Hey Mike,

I'll have you know that the new compressor is the third replacement unit in that vehicle.

I had the compressor and suction line replaced and it got a new expansion valve and dryer to the tune of $800. Then, two years later, the compressor fails again and another $800. gets dumped into the system just before it was sold.

At least the second one lasted five years.

I'm not at all confident that most of these shops get the right amount of refrigerant and the right amount of oil in that system.


One thing that you might check if the compressor is cycling and the vent temps remain too high:

The evap temp switch controls the compressor and if it's not allowing the evaporator to get down close to 35 degrees F., then you'll never cool the interior. In fact, someone on the forum added a resistor inline with the evap temp switch to get a bit closer to the 35 degree figure. Apparently, the typical evap temp switch is not calibrated all that precisely and might cycle the compressor at 42 degrees F. or so.