Vent Temps Unsatisfactory
 

I recently changed the expansion valve in the ol 420 sel and recharged with R-12 with three cans and the vent temps stay around 60 degrees when it's 76 outside with high humidity. I filled it up until full but still no change. This thing used to blow out 40 degrees at the vents no problem. What's the dealio?

Why was this done? leak?
Did you replace the R/D?
Did you pull a vacuum?
3 X 12 oz. cans = 36oz.. My 126 calls for 46.4 oz. Undercharged? 16 oz. cans?

The expansion valve was leaking and the first attempt to fix it failed because I got lazy and only changed the o-rings on the lower lines and the drier. i finally bit the big one and changed the expansion valve and added a little oil and had the system vacuumed and I charged it with three 12oz cans and it resulted in terrible cooling. Then I bought another can of r-12 and filled it until no more bubbles in the sight glass and it resulted in no changes.

Is the car moving when you are taking these temp readings? Or is it sitting in the driveway?

Thats the problem. It cools ok at highway speeds but it is terrible at idle. It is still r-12 and always cooled down to 38-40 degrees no problemo. It struggles to get below 60.

Aux fan running ???

Jumper this sw and see if fan comes ON

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23I0RAMEE24118NOLA&year=1986&make=MB&model=420-SEL-001&category=R&part=A%2FC+Temp.+Switch

:D Arthur, you're getting quite a work-out on the aux fans this year!

i know i have done an aux fan on the 260e

city driving an 90 degree temps are still a bit problamatic...but it will freeze you out on the highway

It's that time of year again...pretty hot everywhere , too...

It is amazing how far along this Forum has come as far as DIYer a/c knowledge...I haven been here since day one, and I can remember when no one would even dare touch their a/c system [ or know anything about it]..so, the Forum has done well on a/c edumacating it's members in this highly specialized field......
There are reg guys here who now know more about their a/c systems than the guy they used to take it to.
Gotta love it ...........

I don't know about my knowing more than the guy I used to take it to, but it sure has helped me. Thanks again!

I can remember when a/c was a new car thing.... our running joke when a guy would ask " "..uuum , What kinda' Gas do you put in there?? "
.....of course our answer was .."High-Test !! "

Aux fan works because when i replaced the drier I bought the little red leads that everyone says go bad and it started working again. Should the expansion valve be hot on one side? I know the front of it gets hot and the back is cold.

<<I bought the little red leads that everyone says go bad and it started working again. >


The red leads ?

Are you talking about the sw with the pigtail leads ?
Do you have gauge readings ?

Yes those leads that go on the drier. I do not have any gauge readings.

if you can get me gauge readings while at idle and at 1500 rpm i can tell you what is wrong with it.

OK... That is the aux fan sw , but very seldom does that sw go bad..people often incorrectly change it b/c they think it goes bad, but the real reason the fan does not come on is b/c they are short of refrigerant [ not allowing high side to get to trigger point of the sw]
..anyway, gauges would be needed for pressure readings.
Did you use an original R12 EV?
..also, You may have overcharged...

I got my 609 cert and bought the R-12 at O'reilleys for 35.99 a can. It took three full cans and som of the fourth. How does this time differ from last time I charged it. A few weeks ago I charged it with only three cans and it blew just as cold or colder than when I put three cans in this time. The only thing thats changed is the expansion valve. could it be bad?

That is why I asked about it being an OEM R12 valve..they make a 134 valve for conversions..

The expansion valve did not say r134a on it like the one I pulled out did. i had a post a little earlier on that and somebody here on the forum told me that the expansion valve didn't matter, but I didn't really worry anyway because the new one didnt say R-134a on like the old one.

Well aother possible is you stated you had someone pull a vac and then you added the R12..but..did you check that it held the vac before adding the R12..in that time frame , it may have not held and in that case , you could have air in the system/// but . not enough info to make a diagnosis..

Gauge readings would help.
Do you see comp cut-out??
Is sight glass clear??
Does fan run right off ?
Is suction line sweating??
Have yo check condenser for debries/air flow??
The EV you took out was 134a valve?? Has this car been converted and you just decided to put R12 back in there??

Lots of questions

I will try to get gauge readings. ( I need to get gauges)
the compressor does not cutoff.
the aux fan comes on after a few minutes. how many minutes I'm not sure.
There are a few small bubbles in the sight glass, but I,ve had more bubbles and it performed better than this. All lowside lines sweat as well as the expansion valve. even though one side of the ev is warm. Im starting to think i need to have the ac revaccumed. Its just hard to find a good shop that still does r-12 on my schedule. The po is a manager at carlysle auto air and told me when i bought the car that it was still r-12 and it still has the r-12 service fittings, and the new compressor has a factory label stating retrofit to r-134a, but was reconverted to r-12. why it had a r134a expansion valve, I don't know. who knows maybe the a/c is working fine and I'm just bummed because this is the first time ive had the car with a full charge of ref. that didn't leak and it performs worse than it ever has before while I was expecting even better performance.

the reason that it said r134 on the valve is that there is no diff between valve for r12 and 134.i went through this back in 1993 and even contacted the manufacturer of the valves.then still being hard headed i ran some tests on same car with two diff valves--no difference at all.

The valves made today are all compatible with both freeze 12 and 134 as well as r12 they will interchange,most companies are reducing the amount of tooling, by making things more interchangeable.