89 190 belt tension ???

[mtavy]

I just replaced the belt tensioner on my 89 190E with 2.6 engine w/AC because I was told by an air conditioning repair shop that was the reason my air is not working. I understand there is a sensor that kicks off the compressor if there is a 15% difference in rpm's between the motor and compressor. I put on a new belt tensioner and adjusting rod but do not know how far to tighten the tensioner. I put on a new pointer and set it to the low end of the wedge shaped scale and tightened it to half way. I read where the tension should be set to the seventh mark on the belt tensioner for cars with AC but mine is a wedge. My question is how far up the wedge shaped scale should I tighten the pointer to?? My air is still not working with the pointer set at half the wedge scale. Thanks in advance. I hope I listed enough information for some advice.

[babybenz]

Hey,
Those tensioners are a total pain to replace. Your indicator should be all the way to the left (passenger) side mark with no tension. As you tighten it will slowly move to the right and should stop at the right most mark.
I bet your AC problem will not be solved with this new tensioner. Does your system have enough freon? Is the compressor turning at all? If yes, Do you see any bubbles in the sight glass? If the compressor is not turning, it could be the clutch is bad (this was my case), no freon, or AC Relay out. With the car running, jump the wires on the receiver/dryer --the cylinder with the sight glass. There are 2 sets of wires-one for fans, other set for the low pressure switch, touch them together for a second to see if the clutch engages. If it engages then the clutch is elimated. Has it been converted to 134A?

[mtavy]

My pointer is almost 3/4 up the wedge scale. What you are saying is it should be adjusted all the way to the end of the scale, correct? I don't know if there is enough freon. I have no way to check. The front plate on the compressor engages when the AC is turned on inside the car. With the AC off the front plate is not turning but when the AC is turned the plate is engaged and turns. There are bubbles in the sight glass. Is this good or bad? Is the low pressure switch the red plastic cylinder that is attached to the dryer near the sight glass? The wires for the aux fans are from a connection that is mounted in a line just next to the drier? With the car running and the AC off, I want to touch the two wires from the red low pressure switch together and see if the compressor engages, correct? No, it has not been converted. The AC was working well until I changed the water pump. Since then, it had worked on and off until now when it is not working at all as far as blowing cold. The fan works just no cold air. I was told there was not enough tension on the belt that is why the AC is not working. Where is the AC relay located and how can it be checked? Thanks in advance.

[babybenz]

My pointer is almost 3/4 up the wedge scale. What you are saying is it should be adjusted all the way to the end of the scale, correct?

correct. Make it 100% up to the scale

The front plate on the compressor engages when the AC is turned on inside the car.

You've confirmed the plate (clutch) is operating and the compressor is turning. No need to jump the wires now--red pigtail connection is the fan operation, the other one is for the clutch. No need to replace the relay which is located behind the battery. Clutch engaging so these parts are working properly.

There are bubbles in the sight glass. Is this good or bad?

Lots of bubbles indicated a low freon charge. This sounds like your problem. Get a shop to charge it with r-12. One can may be all it needs. You ought to see considerable cooling improvement with one can (12 ounces) added.

Your AC guy was right about there being a speed sensor that cuts out the compressor, but if he'd looked in the sight glass and seen the bubbles he would have known the compressor was operational and pushing freon. Better yet he should have attached a pressure gauge to determine how many pounds it was pushing. I'd find an independent import car repair shop--call first to see if they service Mercedes AC.

Good luck.

[mtavy]

Babybenz,
I guess his thought was if the tensioner was bad he wanted to eliminate a possible problem area. That and make an extra $500.00. I spoke with the shop today and told them I had replaced the tensioner but still no AC. He went on about how since the tensioner is ruled out it could be other parts of the system or just a low charge. As far as experience with 190's, I asked the first time I took the car in if they worked on Mercedes and they told me yes. He seemed to confirm alot of the information I had read here on this site. I guess I have no other choice but to go back and have them check for leaks in the AC system and add a charge if necessary. Maybe I"ll mention about testing the system with a pressure gage as you stated so he'll know I some idea of how the system works. Thanks for you input.

[mtavy]

OK. Just got the 190 back from the AC shop. The word is the R-12 was contaiminated by someone who tried recharging the system with a refridgerant with a sealer which ruined the existing R-12 . The system was flushed and converted to the new 134a. The AC is blowing cold now. Now the bad news. I'm told they found a small leak near the expansion valve, I think that was the part mentioned, and the system has higher than normal operating pressure. I think he told me it was near 300 PSI. I was told that the high pressure could be caused by problems with either the expansion valve or the drier. I have to go back in four weeks for them check with a black light for leaks. I was told they would be able to determine which part was the cause of the high pressure at that time. Can any AC experts tell me if this is making sense or are they giving me the runaround? Thanks in advance.