evaluating an AC compressor when system is currently discharged - Page 7 - PeachParts Mercedes-Benz Forum

vwnate1 · #91 05-17-2018, 02:03 AM

Yes, please, do tell what these are for ! .

kuene · #92 05-17-2018, 12:33 PM

OK - so I probed a bit more and figured out the the relay i'm pointing to in photo (nearer the firewall) is the aux fan. When I jumped 30 to 87, the fan spun up.

When I jumped 30 to 87 on the other relay, (engine running, but no AC controls on at the time) the compressor clutch did not engage. I was in a hurry so my testing ended there. Do I need to have the AC turned on from the CCU in order for this jump to trigger the clutch? Do the other pressure/temp switches need to be working correctly too? Or should the clutch engage when I jump those terminals no matter what? Perhaps I should test by hooking up the wires to my new compressor (pre-installing it) Would I be able to sense or hear the clutch engage with the compressor unmounted?

kuene · #93 05-18-2018, 09:32 AM

some have said to check compressor by jumping the low pressure switch on dryer - others have said jump the relay. Do I need the low pressure switch working with pressure in system) for me to jump at the relay? In other words, if I have an empty system, what is the proper way to test (as in where do I jump) if the compressor is getting power?

kuene · #94 05-18-2018, 01:25 PM

Well I answered my own question with some more trial. I was able to get the ac clutch to engage when I jumped the switch at the drier. So that’s good news - power is getting down there.

Here is a new question, along with a new drier I bought new temp/pressure switches. The little brass part circled in red (photo link below) is not a part that came with the new drier or new switch/sensor. Is the new drier a different style, or should I transfer this brass piece over from old one?

https://photos.app.goo.gl/kd3Y9GAHYwG0u1Jl2

Also, I started taking apart some lines. The first one I opened near low side valve appears to have no oring at all. Should there be in this and all similar junctions?

https://photos.app.goo.gl/2MKQ08FN28eCBoSY2

ROLLGUY · #95 05-18-2018, 01:38 PM

Quote:

Originally Posted by kuene

Well I answered my own question with some more trial. I was able to get the ac clutch to engage when I jumped the switch at the drier. So that’s good news - power is getting down there.

Here is a new question, along with a new drier I bought new temp/pressure switches. The little brass part circled in red (photo link below) is not a part that came with the new drier or new switch/sensor. Is the new drier a different style, or should I transfer this brass piece over from old one?

https://photos.app.goo.gl/kd3Y9GAHYwG0u1Jl2

Also, I started taking apart some lines. The first one I opened near low side valve appears to have no oring at all. Should there be in this and all similar junctions?

https://photos.app.goo.gl/2MKQ08FN28eCBoSY2

The pressure switch will fit right on the new drier without the brass piece. Not exactly sure what the brass piece is. Look inside the male fitting, there should be an Oring in there. Yes there should be an Oring at every connection.

kuene · #96 05-19-2018, 08:31 AM

This is what’s in that small brass piece that was attached opposite the pressure switch. Some kind of spring in there, seems like the hex end cap can be used to set the compression of spring. What is this thing?

https://photos.app.goo.gl/GmBcfoBoVfsM2Xfx1

ROLLGUY · #97 05-19-2018, 08:51 AM

Quote:

Originally Posted by kuene

This is what’s in that small brass piece that was attached opposite the pressure switch. Some kind of spring in there, seems like the hex end cap can be used to set the compression of spring. What is this thing?

https://photos.app.goo.gl/GmBcfoBoVfsM2Xfx1

The only thing I can think of is that it is some kind of valve that allows the switch to be removed without discharging the system. That would actually be a good thing if it is just that.

kuene · #98 05-19-2018, 09:31 AM

Sorry, I’ve referred to the temp switch several times as pressure switch. This brass piece is mount on top of dryer opposite the temp switch. Which I don’t think is part of the pressurize Freon system. This this brass piece would seem to have nothing to do with the temp switch.

https://photos.app.goo.gl/w8IBFQpseBP7BQWm1

This thread identifies the part as a pressure relief valve. So is this just some optional thing that some brand of driers have and others do not? On the new beher drier (visible on left in above pic) there is a bolt plug where this would go... I just want to be sure I don't need to install one on this drier.

kuene · #99 05-20-2018, 07:49 AM

I don’t wanna sound drammmatic but man, getting that new expansion valve in was like childbirth. Threading those fixed evaporator pipes right next to each other - at least in this car, was a brutal excercise of mind and fingers. It did not help that this new expansion valve has a slightly different design and has less clearance up against the plastic housing next to it. I hope getting the new one in was worth it, as the internet is still undecided/split if the “r134” valves work ok with r12.

Anyhoo - just one last confirmation on the “pressure relief valve” from the old drier. Everyone is I. Agreement that the behr/hella drier sold from pelican does not need one? I should just leave the bolt/plug in place opposite of where the temp switch is and not put the relief valve on?

ROLLGUY · #**100** 05-20-2018, 10:48 AM

It would have been prudent to flush the evaporator before installing the new TXV. Flushing the evaporator with the new TXV in place may cause any debris that may be in there to get lodged in the new TXV, or spread throughout the system. If the evaporator is not flushed, you don't know how much oil is in there, or if it is contaminated. Also, it is best to use Ester oil after a system is clean and new parts are installed, as it is compatible with all refrigerants. PAO 68 is in fact Ester oil. If mineral oil is used, the entire system will need to be flushed if retrofitted with 134a. Best just to start out with Ester.

funola · #**101** 05-20-2018, 10:51 AM

"getting that new expansion valve in was like childbirth"

You flushed he evaporator already? Expansion valve in the circuit is a big restriction in the circuit and prevents flushing. Same for the compressor and dryer. those components should not be flushed.

The expansion valve is in a tight spot on W123's. You have to be careful not to bend or crack the evaporator copper tubings. There are some tricks I used when I did mine which was a sequence of un-threading the fittings as well as tools I used. I believe I described it as well as posted photos IIRC.

kuene · #**102** 05-20-2018, 05:07 PM

Yes, I flushed the evap before I put new valve in. I also flushed every other line and the condenser. Not the compressor, or the expansion valve. Or the drier - but I’m putting a new one in last step any way.

Interesting on the oil recommendation. I have some no wax mineral oil, but perhaps I should use oil that is compatible with r134 and r12 I case I lose the r12 supply down the road....

So no word on the drier needing a pressure relief valve? The new berh just has a bolt plug - no pressure relief thing. That’s ok?

kuene · #**103** 05-21-2018, 03:58 PM

update.

old compressor removed. There was a very small amount of Oil (half ounce maybe) that drained out - it was brown and viscous, but there wer no clear signs of any debris or gray/metallic sludge. It just seemed very old and dirty - still transparent.

I have three current questions, I welcome any advice/tips and I thank you ladies and gents all in advance.

Question 1. Putting in the new r4. Does anyone have any tips/tricks for managing this task with just my own two hands? When I pulled out old one, I used a jack stand, propped up on a few pieces of plywood, to hold the weight of it in place while I worked out the bolts. This seemed to work pretty well coming out. Also is there a single w123 torque value I should use for the three bolts?

Question 2. I'm still unsure of the receiver drier not having a pressure relief valve (or anything) in one of the top ports. this is the one I have: https://www.pelicanparts.com/More_Info/1238300683.htm?pn=123-830-06-83-M326&gclid=EAIaIQobChMIwI3NscqX2wIV0lqGCh1VSggjEAQYAyABEgL92_D_BwE In 3 of the photos, this is what mine looks like. Opposite where the temp switch screws in, there is just a bolt plugging the port. But in the last picture, which is clearly a different drier - there is a hexagonal thing about and inch or so long sticking out of that port. This is what I've seen in photos of other folk's driers. Do I just not need that part with this Behr? I have the old hexagonal one from my old drier (not original to car), and it seems to be in good shape... I just can't figure out if I'm supposed to have one on the new drier... and if I should reuse (with new oring of course).

Question 3. I'm unable to get any tools to the junction between the rubber high-side line that comes from the compressor, and the hard high side line - this is the fitting that is deep in the engine area, above the high side service port if you are lying on the ground looking up. I don't see how, without uninstalling several other things, I can get the rather big wrenches I need in there. I just can't figure out how to get to this to swap out the o-ring.

Bonus Question Oh shiiiiiit. Was I supposed to use nylog on the expansion valve fittings? On all the hose fittings? (other fittings not a problem since I can easily undo). I wonder if I can unthread the expansion valve just enough but NOT all the way off and apply some while the threads are exposed. I can't go through that childbirth again.

kuene · #**104** 05-22-2018, 01:01 PM

Sorry, giving it little bump.

One of the more pressing questions from the above it whether or not I need to use nylog - especially pertinent to the expansion valve. I will cry if I have to do that over but I REALLY don’t want to go through all this and have a leak. I picked up some nylog today. Should I absolutely put in on the 4 expansion valve connections? Do I put it on the threads AND coat the orings with it? Or just the threads? Or just on orings and not threads? I see some different advice on how bet to use it.

Kill me now for having to redo that f’n expansion valve.

Would I also want to put it everywhere else including the orings/washers at the compressor?

Diseasel300 · #**105** 05-22-2018, 04:47 PM

Surprising that nobody's bothered to answer your questions, including one you've repeatedly asked:

RE: the pressure relief valve. If your system is fitted with a high pressure switch on the receiver/dryer, the PRV is redundant. IMHO it's just something else to leak. None of the newer systems have it and I suspect most of the older ones don't either.

RE: Nylog. It's a great thing to add, but not 100% necessary. If you want to add additional benefits to your O-rings, it's a good idea to use it, make sure you're using the correct Nylog for the oil/refrigerant you're using. Red for CFC (R12) and blue for HFC (R134a, HC, or R152a). If you didn't add it to the TXV, don't feel too bad, it wasn't there from the factory either. If you're using Nylog, smear a thin layer on the O-rings anywhere they're used. If you have a threaded connection, add a bead around the threads before you tighten the fitting down. Try not to get it inside the refrigerant lines.