Another A/C Question - PeachParts Mercedes-Benz Forum

mike240dds · #1 06-01-2011, 11:45 AM

Ok first let me start off by calling myself a moron. I am trying to get my a/c up and running since it is almost 100 degrees here in middle Georgia already. Over the weekend I took my car over to a friend to check/charge my system. The car was already converted to 134A by a previous owner. Well I left the car in his capable hands while I went and did some family stuff. I come back in two hours to help and there is refrigerant spraying out of the low pressure switch on the receiver dryer. I asked him what the hell?? Long and short of it he does not know what the hell he is doing. So we agreed he will never touch my car again.

I got the car home and checked for any leaks or blown out hoses I did not see any dye coming from any of the fittings. Jumped the a/c compressor it kicked on jumped the aux fan it kicked on. I did notice a drip of oil on the passenger side floor mat. I took down the plastic cover and the insulation was covered in oil. I am assuming I need to replace the expansion valve at the very least. Now my plan is to replace the expansion valve and vacuum the system to check for any additional leaks.

What else should I be looking to check or replace? Also is there supposed to be some sort of pressure relief built into the low pressure switch? At first I thought it was toast but inspecting it closer there is a small plastic valve in between the prongs which is where the refrigerant was spraying out of.

Car is an 83 300d

Thanks in advance

1980sd · #2 06-01-2011, 02:37 PM

You have AC compressor oil in the passenger footwell?

mike240dds · #3 06-01-2011, 02:59 PM

Quote:

Originally Posted by 1980sd

You have AC compressor oil in the passenger footwell?

Yes the expansion valve is located under the dash on the passenger side of the car.

thayer · #4 06-01-2011, 03:30 PM

Sounds like the least that needs to happen is order a new TX Valve and Receiver Dryer. Install with Fresh O-Rings then fill it with nitrogen (I'd have to get a friend to do this) to test for leaks. Then if there are no leaks, draw a vacuum on it and then filler back up with 134 with maybe a few drips of ester oil in the R/D and motor right along. Not too much oil. Its better to be a shade low on Comp oil than too much. Just ask my last two Compressors.

280EZRider · #5 06-01-2011, 06:49 PM

I have never heard of a "pressure release" in the low pressure switch. There are, however, switches available that will cut out the compressor in the event of either a low or high pressure situation. I would replace this switch as well since it was spraying. The single low-pressure switch is half the cost of the hi/low pressure switch.

Since you have the system open, you might as well replace all the seals. They´re cheap and since the system has been converted, you never know what might have been missed.

Don´t forget that after a vacuum has been drawn, you wll need to jump the low-pressure switch to supply power to the compressor for charging.

engatwork · #6 06-01-2011, 07:50 PM

Give me a call and bring it over and we'll make it right with the real stuff if you want.

rscurtis · #7 06-01-2011, 08:24 PM

It could be just the "O" rings on the TX valve. That cured an annoying slow leak I had on my '83, espescially when I let the car sit. If you're going this far into the system, purge it and convert it back to R12. I haven't had to touch mine in four years and it still works fine.

leathermang · #8 06-01-2011, 11:54 PM

Ok, Since you have a documented oil leak they safest thing to do is to do a complete evacuation/flush and measure the proper amount of oil back into the system.... there is no way to check to see how much oil you have in the system... The only way is to clean all the old oil out and put in the proper amount. If you have an R4 Delco you have no oil sump..so all the lubrication provided to your compressor is in the form of oil dissolved in the refrigerant...
I would not assume you needed to replace the Txvalve given the info you have provided. But you might want to just due to its low cost and the fact you will have the system opened up to flush it.
Some cars have a blow off valve... my 95 Lincoln does...and it can not be bought anymore.. my mechanic had to find one in a salvage yard to replace mine..... my blow up was due to excess pressure caused by the electric fans quitting.
So, normal procedure would include all orings of the proper color, a bottle of Nylog of the proper color, Txvalve if you want to or think it is needed , flush solvent, new cold flow 500 Castrol refrigerant oil unopened until you are about to install, reciever/dryer unopened until actual installation , cleaner for fins of condensor and radiator, fin card for same, new pressure switch and temp sensor on receiver/dryer assuming they do not come with the new one...
That may not be all... just all I can think of off hand...
You need to do a lot of reading in the archives.... and start with the sticky at the top of the page on AC...

mike240dds · #9 06-02-2011, 08:27 AM

I went ahead and ordered a new receiver/dryer, pressure switch, and expansion valve. I have a package of A/C O rings. I figure I may as well replace them since the system is going to be opened up. I plan to blow out all the lines as well. Hopefully my parts will be in tomorrow so I can get started this weekend. Hopefully everything will go without a hitch, then I need to figure out whether to keep the 134a setup or go with r12.

engatwork · #10 06-02-2011, 08:57 AM

You will want to add the proper oil during reassembly for whichever refrigerant you chose. You can purchase blow out material from the local auto parts place. Disconnect everything and blow out the hoses too.

engatwork · #11 06-02-2011, 11:38 AM

Here is the p/n for the AC Delco o-ring kit for the car.

tangofox007 · #12 06-02-2011, 11:42 AM

Quote:

Originally Posted by mike240dds

... then I need to figure out whether to keep the 134a setup or go with r12.

In Georgia, R-134a will serve you well in April and October. Don't waste your time with it.

leathermang · #13 06-02-2011, 02:46 PM

Quote:

Originally Posted by mike240dds

I went ahead and ordered a new receiver/dryer, pressure switch, and expansion valve. I have a package of A/C O rings. I figure I may as well replace them since the system is going to be opened up. I plan to blow out all the lines as well. Hopefully my parts will be in tomorrow so I can get started this weekend. Hopefully everything will go without a hitch, then I need to figure out whether to keep the 134a setup or go with r12.

The pros suggest using Nylog on those o-rings of the proper color for the refrigerant you are using. It is cheap and you do not want to take any unnecessary chances on having to redo this tedious operation.
You need to flush the lines.. not just blow them out... particles get embedded in the oil on the inside of the lines...
Given where you live....and how much trouble this operation is... and the relatively low cost of the BEST refrigerant ... I suggest you go to R12...