evaluating an AC compressor when system is currently discharged - Page 6 - PeachParts Mercedes-Benz Forum

vstech · #1 05-16-2018, 10:01 AM

I have never removed anything else when changing compressors... should drop straight out.

kuene · #2 05-16-2018, 03:37 PM

Awesome. Thanks vetch. I found the belt page of the manual too.

kuene · #3 05-16-2018, 10:25 PM

Is one of these relays for the compressor and one for the aux fan? Or am I lookin at the wrong relays.

https://photos.app.goo.gl/CsZo2IyjVtiQy8322

vwnate1 · #4 05-17-2018, 02:03 AM

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

kuene · #5 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 · #6 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 · #7 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 · #8 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 · #9 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 · #10 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 · #11 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 · #12 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 · #13 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 · #14 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 · #15 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?