How common is drier/accumulator failure. - PeachParts Mercedes-Benz Forum

1980sd · #1 05-19-2011, 01:55 PM

I have a 134a conversion label on my car dated 10/11. The AC is cooling but the low pressure switch is cycling. I put 2 small cans (1 lb I think) using a cheap consumer grade gauge and only got to about 12 psi. The 2 cans did raise it from about 8 psi.

For some reason I'm EXTREMELY PARANOID about my drier going out and flooding my system with junk! I plan on having an AC shop replace the drier and pressure switch in the near future.

So, do I have reason to worry? Should I put another can of 134a in it or just wait until I have pros do it?

Thanks.

leathermang · #2 05-19-2011, 02:25 PM

They do not fail very often because most people know to replace them when the system is opened or compromised... so they are typically the newest hard part of the system at any time...
If left long enough OR subject to too much vibration I think the sacks holding the desiccant are subject to rupture ( some units have wire mesh instead )......
If you are worried either that it will break and mess up things downstream..
OR that it is not functioning as a dryer ( having been ' soaked' ) .. then by all means have it replaced... the cost of the unit is very little compared to the consequences of either of the types of failure I just described... The labor is the higher cost of the procedure....

1980sd · #3 05-19-2011, 03:32 PM

Thanks. I'm currently getting the car up to speed (Not sure if it'll ever be 100%) and figured that I'd have the system evacuated, new oil put in, a new drier, new low pressure switch and recharged.

Yea, the drier is about $20 and the switch costs about the same.

leathermang · #4 05-19-2011, 05:14 PM

Remember that you need to take out the old oil by flushing to make sure you have ' just the right amount'.... too much or too little can crash the system...
Typically about 6-8 oz spread around the system as it is put back together...

Yak · #5 05-19-2011, 05:59 PM

If the low pressure switch is coming on, maybe the pressure is low. Time for a leak check. Look around your system fittings for green oil. Drop the passenger side footwell panel and look at the TX valve in there, too.

Harbor Freight sells a cheap 134a manifold gauge set. Maybe useful if you're going to troubleshoot yourself. Maybe not if you're already converted and going to a shop.

I endorse the leak check with positive pressure and not just the "it held vacuum for 30 minutes" method. Mine held vacuum, then leaked at the compressor manifold under pressure. That cost an extra evacuation and charge since the first one leaked.

1980sd · #6 05-19-2011, 06:10 PM

Quote:

Originally Posted by leathermang

Remember that you need to take out the old oil by flushing to make sure you have ' just the right amount'.... too much or too little can crash the system...
Typically about 6-8 oz spread around the system as it is put back together...

The shop said they pump it down to remove the refrigerant and then change the part, add 2 ounces per component plus dye, then re-charge and test.

Does vacuuming the system remove the oil? I'd imagine it is throughout the system hung up everywhere...

I was fooling with it today and had some kind of AC explosion or something... WHY did they make the friggin' dye look like coolant

Gonna let it rest for a day or so...

Yak · #7 05-19-2011, 06:37 PM

Quote:

Originally Posted by 1980sd

The shop said they pump it down to remove the refrigerant and then change the part, add 2 ounces per component plus dye, then re-charge and test.

Does vacuuming the system remove the oil? I'd imagine it is throughout the system hung up everywhere...

I was fooling with it today and had some kind of AC explosion or something... WHY did they make the friggin' dye look like coolant

Gonna let it rest for a day or so...

Does "fooling with it" mean you started to open up a pressurized system and an "explosion" of flourescent green-oil laden gasses escaped? That'll happen if you don't evacuate the system prior to maintenance...

leathermang · #8 05-19-2011, 07:06 PM

Vacuuming does not remove the oil.
" AC explosion "... I think you are beyond my ability to help.

1980sd · #9 05-19-2011, 07:28 PM

Well, I've been sorting the vacuum part of the system and it's pretty much a done deal

While working on it the low pressure switch started turning off the compressor. (I checked the switch with a meter just to make sure it wasn't something else.)

It was cooling pretty well but I figured it needed some 134a since the pressure switch was cycling.

I got one of those cheapo DIY kits and followed the instructions. At first the gauge was about 10psi. I put 2 small cans in and it came up to about 20. I got another can (The target according to the gauge was 40-50 psi) and was shooting for about 35 psi. About 25 psi there was something like a fire extinguisher under the car for about 3 seconds

WTF!!

I checked out the compressor and found dye around one of the O rings at the back of the compressor (It's a round Delphi GM type) and a big puddle under the car.

There was some "Growling" coming from the compressor but it was subtle and seemed to be subsiding as I added 134

I started the engine and hooked the gauge back up and it seems to be holding at 20 at that time. The engine has been off for a few hours and now the gauge is well into the red

Not sure if that's an accurate measurement of anything.

So, where did I screw up or did I just have a failure? It was cooling (Pretty well actually) before I started working on it.

I just fired it up to pull all the way into the garage. (It's longer than it looks

)

Anyway, I let the engine warm up and started the AC and the gauge held at 25. I figured with a blowout like that it'd be empty. Seemed to be cooling OK...

vstech · #10 05-19-2011, 08:57 PM

some systems have a HIGH pressure dump... sounds like either it's bad, or you put in too much freon.
likely the aux fan isn't coming on, and the system is building too much head pressure while you are charging.
ya need a full charging manifold to know what is going on.

1980sd · #11 05-19-2011, 09:16 PM

No the aux. fan was running and seems to cycle OK. It looked like some freon just escaped through the O ring and then stopped leaking

I was thinking that some kind of blow-off valve released because it stopped venting s rapidly as it started

Maybe the High dump you are referring to? I couldn't find a valve or anything.

Are you saying the high pressure dump could be bad?

I need some gauges and a vacuum pump if I'm gonna keep fooling with this stuff...

I'm sure that with the right tools I could figure it out.

vstech · #12 05-19-2011, 09:23 PM

Quote:

Originally Posted by 1980sd

I'm sure that with the right tools I could figure it out.

yup.
and without them, it's very difficult to find this kind of problem.

vstech · #13 05-19-2011, 09:24 PM

if your aux fan is working, it's likely you have blockage in the coil. your condenser could be jammed with bugs/dirt

Yak · #14 05-19-2011, 09:53 PM

Identifying the seals on the back of the compressor will also be important.

If they're actual O-rings, look for funola's compressor rebuild thread to get the proper oblong cross section part.

If they're rubber+metal sealing washers, you'll need to check if they're the black ones (2 same size) or the yellow and green ones (I think, maybe yellow and red). Regardless, if they're leaking they should probably be replaced.

You should also check to see if you have the high pressure cutoff in the receiver dryer switch. They should be installed in any 134a conversion. They're called something like bi-switch or dual-switch. They're still plug and play with the receiver dryer, but they're a safety valve on the 134a conversions. Not pricey, just add one to the R/D order.

Zacharias · #15 05-19-2011, 10:05 PM

How common, you asked?

On my '79 SD, three things went on the cc in eight years: the pushbutton panel, the receiver/drier and finally the condenser (which was where I gave up fixing).