2003 Merc C240 - Can't get any 134a in the system

[rgnprof]

My first post here - I replaced the compressor on my son's C240 years ago - maybe 6-7?? Never charged it up - did put the right oil in it. Not a car that he drove that much, so wasn't a priority. Just completed a bunch of work and went to recharge the AC. Drew a good vacuum and it held overnight. But I have tried to get r134a in 2-3 times now and I just can't get anything in to the system other than air! I know I'm getting that, because when I pull the gauges off and depress the schraeder valves, that's all I'm getting out - AIR!

I believe this is the clutchless compressor, so I'm having some trouble telling if the compressor is ever cycling on. I know it should kick on maybe at 60 psi (??)...

I'm not a pro, but I'm not an AC novice either. Just recharged my Subaru after tracking down some leaking o-rings, rebuilt my Ford E350 AC, but I'm not sure what's going on here? What am I overlooking?

Any help?

Thanks,
ryan

[tbirdtbird]

How can you be getting air OUT if you are putting in 134?
134 has no color , I believe you are not getting AIR, but 134 back out.

This happened on this forum about 1 year ago from another poster

[atikovi]

How are you charging it? With cans? A drum? A set of gauges? From the low or high side? Need more details.

[rgnprof]

Sure feels like air - not very cold. I've seen 134a come out and this is not like that!

I am using gauges, charging from 12oz cans and only through the low side. - car running, revving to 2000+ rpms. System takes 28oz.

[JohnHere]

Make sure that the adapters are securely attached to the test ports on the car, that the thumb-wheels are open (turned fully clockwise), and that the HP hand-wheel is closed on your Manifold Gauge Set while charging.

Check to ensure that your small cans don't contain any sealer. Sealer is bad news for an A/C system and will cause serious problems that you didn't have previously.

Unless someone purposely pumped air into the system (looking for leaks, maybe), chances are it's refrigerant coming out.

[rgnprof]

Thanks John - I have done all of the above. I just got done using the same set of gauges to successfully recharge my Subaru Forester. I guess it's possible that the low pressure connector is not fully depressing the schrader valve, but it is drawing a vacuum and if I open the blue adapter valve I can hear "air" escaping...BY HP, I'm assuming you mean High Pressure - and it is definitely closed.

I never use sealer - maybe a bit of UV dye but I haven't even done that here. There is no way I pumped it full of air - on purpose. I an drawing an almost 30in Hg vacuum and then directly TRYING to add refrigerant from there.

When I first open the low pressure valve I can feel gas going in - the can gets cold - and then it stops - pretty quickly. I am shaking the can, rotating it from 12 - 3, putting it in a pan of warm water...I just can't get the system filled. The air escaping - when I depress the schraeder valve is not 134a COLD - it's ambient temperature, maybe a bit cooler.

[JohnHere]

The compressor should be running with the engine at about 1,800 RPM to draw the refrigerant gas (can right side up) into the low side. If it's not running, the refrigerant will stop flowing from the can into the system because the pressure inside the system and can will be the same.

If you're charging into a well-held vacuum and then depressing a Shrader valve, it has to be refrigerant that's coming out. There's nothing else but oil in there. Don't open the system to the atmosphere while it's under a vacuum, though. Doing so will only draw-in air and moisture, which you definitely don't want.

[rgnprof]

Yes - I'm careful about not letting air IN to the system. I'm guessing then - from your last post - that my compressor is not running. On a regular, clutched compressor, I can easily see the clutch engaging, but on this clutchless compressor (Denso 471-1474), I'm not sure what's going on.

It sounds like I am getting some in, but then - as you stated - the pressures are equalizing because the compressor is not cycling on.

Is there a way to test this?

I know jumping the compressor to ON is generally not a good idea - any suggestions?

[JohnHere]

Looking up the Denso 471-1474 compressor for a 2003 M-B C240, which ostensibly is the correct OEM compressor for your car, the description and specifications from Denso say that it has a clutch. Going by its outward appearance, it also looks to be a variable-displacement compressor having an electronic control valve.

Are you sure that the compressor you have is clutch-less?

Presuming the above compressor actually is the one you have, and the clutch isn't engaging, the problem could be as simple as the clutch air gap being too wide. From the new compressor photos, it appears that you won't be able to slip a feeler gauge between the clutch "drive" and "driven" plates to measure the gap. Alternatively, try (very carefully) nudging the center of the clutch with a piece of wood, like a two-foot-long two-by-two. You'll need to have the engine running and the A/C system turned on for this test. Again, use extreme care when doing this, avoiding any other rotating parts. If the clutch suddenly engages by nudging it, you'll know that the gap is too wide. The fix is either disassemble the clutch and remove a shim, or replace the clutch assembly with a new one.

If the clutch doesn't engage after nudging the center plate, then you might have deeper problems with a bad relay, open wiring, or faulty clutch windings.

You might also have a clutch that's actually engaged, but the compressor is running at virtually zero displacement and pressure due to a faulty control valve.

Lastly, connect a scan tool to the car (or have it done) to determine whether any stored trouble codes appear, specifically for the A/C system.

[Tim]

No Clutch Coil.

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