It's getting pretty hot here in Sydney so I've started to use the AC. I've been using it regularly now for a week and its been great - it pumps out very cold air.

After last weekend's trip out of Sydney I've noticed some noise when I which the AC on as well a more load on the motor at idle and low speeds compared to when I started to use it a week ago.

The noise stops at higher rpms and I don't notice the load (of course due to the all ready higher rpm).

It is still pumping out very cold air but I'm a bit concerned if the AC compressor needs maintenance/lubrication top up???

The MB Star Classic CD is a bit ambigious - describes how to drain but very sketchy on how to refill but clear on determining the volume of oil replacement.

If I do decide to attemp to refill the oil, do I need to get the Liquid Air refrigerant(freon replacement) professionally drained first? Is the oil resevoir a seperate system from the refrigerant resevoir(I've got my fingers crossed...)?

Thanking you in advance, looking forward to your advice.

Ysmael

What engine do you have?

It may not be compressor noise that you are experiencing. It may be a worn drive belt, belt tensioner of belt tensioner shock which will all make noise when the a/c is on at idle.

To drain the oil out of the compressor would require the removal of the compressor or a comprehensive flush of the system with nitrogen. As long as you don't have a leak, I wouldn't worry about it.

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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32

Hi Alex,

You might have a point, I've just raised Tobias up on the stand and poked my head underneath and the noise (squeaking) isn't coming from the compressor but I still can't isolate it (...ran out of time for today). It seems to be coming from the AC clutch pulley.

Thanks for the advice, will continue looking tomorrow.

Cheers,

Ysmael


- the engine is the 3.5L V8

Hello,
Spray some water onto the v-belt that drives the a/c compressor and check if the noise goes away. If you have not replaced ALL the v-belts and there is no evidence(receipts)of it having been done in the last two-three years, just junk all and fit new v-belts.
Hope that helps.

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Nachi11744

Or if you go the oil change route, might not be a bad idea on the '72, freon garage can drain the system and store the gas and then put it back in.

Okay, here's what I tried - I sprayed the v belt with some water while the clutch was engaged and it actually made the belt slip with a loud piercing squeal and the compressor pulley coming to a halt. Thanks nachi11744 for that simple tip.

So it's obvious that the belt needs to be tensioned a bit but if this fails I will replace the v belt (I can't find any record of when the v belts were last replaced...) - looking at the set up it looks straight forward but I'll just have to read up on how to do this first...

Cheers,

Ysmael

Kind of hard to tell without knowing what compressor is being used, BUT the slipping belt and increased load indicate to me that something is going on with the compressor. You should definitely get the oil level checked as well as the high and low side pressure. Maybe too much freon and with ambient temperature increasing the pressure? Or a bad expansion valve?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I've just removed and inspected the v belt that drives the AC and it looks in great shape and fairly new but before removing I checked the tension on the v belt and there wasn't much tension at all.

I've replaced the original belt and re-tensioned using the tensioner pulley and all of the noises are gone and no more slipping. Is there a simple way to determine the correct tension required? Are there ramifications on an over tensioned v belt? I've only done it on feel ......

I've taken Tobias for a test drive and all seems to be fine in the noise and slippage department and really cold air but I do feel a more than usual load on the motor at low revs plus a sound and feel thats similar to the clutch fan engaging, then all okay when the revs come up. Then again it might be the clutch fan working...

I don't mean to sound so incompetent but this the first real high temps in Sydney in the last three days (35- 42 degrees celcius) since I've had Tobias it's just now I've noticed the changes. I just don't want to destroy anything that can be easily avoided.

Having said that - thank you Chuck Taylor and 240DieselDog for your advice, I will get all the sugested points checked. I'll just have to find someone that's knowledgable with this type of AC over here.

Is topping up the AC compressor oil a non-DIY exercise even if I get the refridgerant professionally removed and restored?

Cheers,

Ysmael

Hi

Just my compressor oil topped up and there is a big difference in the power of the engine after that. I can't believe that the compressor was causing that much drag too. I didn't do it myself but I saw the a/c guy remove one of the hose connectors and pour in a few ccs. About half a cupful maybe. I think it has to be special oil and measured. Usually there is a hole somewhere on the compressor where you can insert a dipstick to check. Most shops just put in a measure of it.

Oreo

Hello,
You posted that the drag increased after a few days of use, did you turn *up* the thermostatic setting to increase cooling?
It may be that you need to check and top up the compressor oil, but anything that you open on an a/c system, eg. the compressor oil fill plug, will leak the a/c gas.
Have to get an a/c tech to look at it, that would be the best course of action.
Have a good week.

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Nachi11744