a/c repaired, road test (trip), now for a cooling check - PeachParts Mercedes-Benz Forum

CSchmidt · #1 07-21-2003, 12:11 AM

Folks,

A couple of months back I posted the compressor on my 87 sdl died. After pricing a new at around $700 and having my job end, I decided on taking a chance on a $250 rebuilt from the place on ebay. They had a special with no core needed (my was frozen and no-good). It took a while for them to send it out and even answer the phone, but it arrived and was correct with the receiver/dryer as well. Next is scheduling the trip (200 miles away) to my a/c repair buddies place.

The Repair:

We get started on a Sat am in his very pleasant garage with all the right tools. Thanks to the help and recommendations I was able to take the compressor out from the bottom pretty easily. I disconnected the manifold line and left the hoses in the car. now the fun starts.

We did the recommended end to end flush flush flush.... The results went from black to clear, so hopefully it is clean enough. Thanks again for the word of experience here from many and it was taken to heart.

The rebuilt has 2 "flaws". First is the rebuilt compressor in/outputs are horizontal, and it doesn't have the fittings that connect to the manifold pipe and make the openings vertical. The bolts holding the fittings on the old compressor are ^&*#$% tight. We do free them up successfully, and bolt to the rebuilt. Next is the speed sensor at the back of the rebuilt has the electrical leads snipped off..... We pulled the one from the old compressor (held in by a snap ring). It is still in good shape and it doesn't effect the internals or sealing of the compressor. We removed the one from the rebuilt and it had a big chunk taken out of it, so maybe they snipped the leads to prevent us from using it..??? So the original speed sensor is replaced with wiring into the rebuilt. We also checked the oil quantity (was correct) from the compressor and replaced it.

Time to snake the rebuilt into the car. My buddy has a nifty cover plate (Ford application) that prevents any oil from leaking from the holes where the manifold pipe attaches. Ten minutes later it is re-installed and the manifold attached. We evacuate for several hours, stop and check for leaks, then pump again for a bit.

One last snafu, the rebuilt came with a pulley about 1/2" larger in diameter. The old belt won't fit, so off to the auto parts store in scenic Zebulon, NC. The new belt fits fine and time to charge. We loaded (I believe) 3 cans of R134 in the system. This should be close to the 80% guideline I have heard for 134 working in R-12 designed systems. No bubbles in the sight-glass, but the sight glass is "milky". Output is wonderful! A local test ride on a 90* day yields great cooling. I didn't have a thermometer that day or didn't get the final pressure guage readings - but my A/C friend thought all was good. Total time was about 6 hours, a success in my book.

The Road Test:

The 200 mile ride home - all worked great. A week later is my ---ahem -- 30th high school reunion in Buffalo. A roughly 2000 mile road trip with detour to central PA, and all works great from the A/C side. I believe I am approaching marginal cooling on the radiator side. There is a VERY large hill at the start of the trip going from NC to VA. About 7-8 miles of 5% + slope if I remember correctly. Steep enough there are 2 or 3 truck emergency run-off points going downhill. I held the car (in 85*+) weather to about 70 mph. Then backed off slightly when the temp guage showed a needle width over 100*. It stayed stable at 100* for the remainder of the climb. I had been needing an "Italian tune-up" for a while. All was fine except the oil pressure guage is now stuck at 3. (more on that later). I complete the rest of the trip with no temp issues under ordinary conditions. Frequent steady highway cruising at 80 mph (outside temp is 85*) and the engine temp stays around 90-95* on the guage - until I come down I-81 to VA Rt 501. 501 is a very hilly up and down climb going over several 2000-3000 foot hills. Going up the switchbacks (100 yards of straight, 180* corner, 100 yards of straight...) with the A/c on sent the temp guage beyond the 1 needle width over 100* that is my personal limit. A/C off and slow down a bit and the temp is under control at 100* or less. With the records I have, my radiator was replaced about 5 years ago with a new one, but it has green antifreeze in it. Is the common wisdon here that it is time to check/replace the radiator? Is this level of cooling typical or heading below normal? Just as with the A/C recommendations, I have taken to heart the "DON'T OVERHEAT A 603 ENGINE" warnings. I expect when I find a job I'll invest in a new radiator.

Now for that rascally oil temp guage. It worked fine prior to the trip (245K miles). It initially froze at 3 after the hard hill climb then the motor cooled off on the downhill side - going at 80 mph. I speculate that the climb may have allowed the pressure sender to move farther than usual whle going uphill then was caught as the engine cooled on the downhill side. The guage stayed at 3 even with the key off (the other guages work correctly). Then another warm hill climb on the way home, 1000 miles later. The engine gets up to 95* for an extended climb. It now stays at 3 when the engine is on, but goes back to 0 at shut-off. Faulty sender unit?

I found a sender type connection - drivers side way down low on the oil pan. I expect this is an oil level sensor. Removed the electrical connection, cleaned and replaced. Did the same for a connector at the base of the oil filter housing, more likely the oil pressure sensor? No change in actions, engine off = 0, on = 3 even at hot idle (was 1.8-2.0 before trip). Suggestions?

Thanks again for the support and assistance here. The 2000 + miles in the car over the last few weeks has been great. I averaged around 26 mpg at good speeds, in some hilly country, with the a/c on in a wonderful car. It provided me a well needed mental "tune-up".

Chuck

psfred · #2 07-21-2003, 07:49 PM

Chuck:

What an adventure! You did the right thing with the speed sensor, by the way -- won't run if it isn't working.

My mechanic friend always installs a filter in the suction line when replacing a compressor, he's had too many rebuilds rejected under warrenty replacement because of "contamination" -- even if he has replaced all the rest of the system!

I think you have a bad visco clutch, and as a result are running too hot from poor fan performance. Check it next time it gets that hot and you can pull of -- it must stop within one revolution when you shut the engine off. If it spins more that that, the clutch is bad. Do a search for a way to replace the silicone fluid rather than the clutch!

I also wouldn't worry too much about 100C, the cooling system is pressurized to 20 lbs, it won't boil until 120 C or greater.

I would suspect the oil pressure sensor, I'd bet the spring failed. The one on the pan is the low oil level sensor.

Peter