W126 R12 pressure advice - PeachParts Mercedes-Benz Forum

James L · #1 05-10-2007, 06:12 PM

1984 300SD; 83 degrees ambient

idle; low side 50, high side 210
2000RPM; low side 30, high side 225

vent temp will not get below 60 degrees

sight glass bubbles, then cloudy, then clear, aux fan works.

Flushed lines & evaporator
new rec/dryer, new expansion valve, new a/c hoses, new condenser
new evap temp sensor, rebuilt Behr R4
4-12oz cans R12 (48oz-3lbs)
6.7 ounces mineral oil
uv dye

vacuumed 2 hours, held vacuum, no visible dye leaks, no beeps on the leak sniffer.

possibles causes?
bad expansion valve
weak compressor
air, moisture non-condensables in system
blend door issues
monovalve

Is it undercharged-should I add another half can of R12? overcharged? should I reclaim, recycle, re-vacuum and recharge?

I am truly frustarted this is the third year of spring a/c work on this old money pit. I spent alot of money and time on this again. I am getting too old and too poor for this. Thanks for any advice.

rbardolv · #2 05-10-2007, 06:35 PM

It sure sounds like you know whats up, but take a look at this... http://dieselgiant.com/repairyourac.htm

He says exactly what he put in , and has done and test results...

FWIW, Its my point of reference..

Cheers!

rbardolv · #3 05-10-2007, 06:37 PM

PS.. ALso take a look here: http://www.es-refrigerants.com/

..especially the "refrigerant support" products.. It sounds like it could help ya.

dannym · #4 05-11-2007, 08:01 AM

The high side is right but he low side is way too high. It sounds like you did everything right except I would have kept it in a vacuum overnight and hit it again for another hour the next day before charging.

What did you flush with?

Also you mentioned Mineral oil. Is that the proper mineral based R-12 refrigerant oil? Where did you come up with 6.7 ounces? that seems like a lot.

Danny

James L · #5 05-11-2007, 09:55 AM

dannym, The oil info I averaged from the info that is all over the map; (as in correct R12 weight 2.1-3.5 lbs) data from the service cd, enclosed R4 instructions, alldata, this site and others; info ranges from 8oz, 6.7 oz (max in service cd), 6 oz, 5.6 oz.

Flush solvent; first used the $15 aerosol a/c flush with hose from advance auto, followed by mineral spirits and lastly brake cleaner, this was followed by alot of shop air to insure all was out. (this was done numerous hours back and forth with drilled out expansion valve and without).

Mineral Oil; BVA 4 is a wax free napthetic mineral oil only for CHCF refrigerants like R12 and R22, it has better flow at 300 visc, used Castrol 500 visc mineral oil (5.6oz) last year and had compressor failure, wanted the best mineral oil I could find.

More background; a/c project was finished about 3 weeks ago. went on interstate 2 hour drive, vent temps were about 58 at 85 ambient. Noticed the expansion valve and low side return hose had ice (looked like dry ice) ETR probe was not pushed in enough (although I do not think this was the cause of the ice). went on driving 3 more hours to the mountains (Asheville) and was getting 38 degree vent temps. I was worried about evaporator freezing so I had to monitor vent temp with probe and switch to high fan, economy or off to get vent temps up.

The expansion valve I used was the $19 APA from ********az. I am starting to think I got a bad one and it may be too open (reason for the high low side), also expansion valve o-rings may not have seated right, who knows. (W126 expansion valve work is such fun back bending work). I may order the $35 German one.

Other thoughts;
1.add a half a can of R12
2.clean evaporator through blower hole for blockage
3.reclaim, recycle, re-vacuum (30 minutes, then hold overnight as dannym said, then a full 4 hour vacuum with heat)
4.reclaim again, new expansion valve, re-vac again.

advise, thoughts please
thanks

dannym · #6 05-11-2007, 10:11 AM

Over oiling will definitely reduce capacity a lot. I thought the oil charge was 6 oz but I could very well be wrong.

I wouldn't add more refrigerant the correct charge is 2.9 pounds and you used 3.

It sounds like you really did a good job. My only question is how hard was it to flush the condenser? Were you able to flush it out good and fast?
Was there ever any stop-leak added to the system?

Danny

James L · #7 05-11-2007, 10:31 AM

dannym, condenser was new, did not get flushed. No stop leak or the like in the system, this is the third year of flushing.

would half an ounce too much oil really matter?

SD Blue · #8 05-11-2007, 10:59 AM

Double check system capacity reference.........for some reason the Haynes manual lists 56oz. as refrigerant capacity for years '84-'86.

Carrameow · #9 05-11-2007, 11:32 AM

Where are you getting R12? Secret stash, huh...

vstech · #10 05-11-2007, 11:39 AM

Quote:

Originally Posted by James L

dannym, The oil info I averaged from the info that is all over the map; (as in correct R12 weight 2.1-3.5 lbs) data from the service cd, enclosed R4 instructions, alldata, this site and others; info ranges from 8oz, 6.7 oz (max in service cd), 6 oz, 5.6 oz.

Flush solvent; first used the $15 aerosol a/c flush with hose from advance auto, followed by mineral spirits and lastly brake cleaner, this was followed by alot of shop air to insure all was out. (this was done numerous hours back and forth with drilled out expansion valve and without).

Mineral Oil; BVA 4 is a wax free napthetic mineral oil only for CHCF refrigerants like R12 and R22, it has better flow at 300 visc, used Castrol 500 visc mineral oil (5.6oz) last year and had compressor failure, wanted the best mineral oil I could find.

More background; a/c project was finished about 3 weeks ago. went on interstate 2 hour drive, vent temps were about 58 at 85 ambient. Noticed the expansion valve and low side return hose had ice (looked like dry ice) ETR probe was not pushed in enough (although I do not think this was the cause of the ice). went on driving 3 more hours to the mountains (Asheville) and was getting 38 degree vent temps. I was worried about evaporator freezing so I had to monitor vent temp with probe and switch to high fan, economy or off to get vent temps up.

The expansion valve I used was the $19 APA from ********az. I am starting to think I got a bad one and it may be too open (reason for the high low side), also expansion valve o-rings may not have seated right, who knows. (W126 expansion valve work is such fun back bending work). I may order the $35 German one.

Other thoughts;
1.add a half a can of R12
2.clean evaporator through blower hole for blockage
3.reclaim, recycle, re-vacuum (30 minutes, then hold overnight as dannym said, then a full 4 hour vacuum with heat)
4.reclaim again, new expansion valve, re-vac again.

advise, thoughts please
thanks

OK, first, if you have ice two things could be wrong. low charge or obstruction, either with airflow, or expansion device.
if you put in correct charge, and there is no leaks, that leaves flow of air of freon.
suspect dirty evap, or slow blower.
also, you did a great job of cleaning out the pipes, flushed great, chemically removed all oil and such, then ruined it by pressurizing and clearing out the system with shop air.
there is oil and water in shop air. both of those are bad for the a/c system.
vacuum pump can remove water, if pumped long enough, but not oil. I would dump the charge, flush again, and then blow out with dry nitrogen, or pure 134a NOT THE "KIT" 134 stuff from store.
then recharge with oil and refrigerant. too bad the compressor oil could also be compromised. I do not know if compressor oil can be removed. compressor replacement may be needed.
sorry.
John

Carrameow · #11 05-11-2007, 11:53 AM

Please forgive my ignorance and disrespect and my 2cents, but my take is maybe all this mapping, and thermodynamic analysis and Thermodynamic cycle efficency analysis might be overkill for 300D Automotive Air conditioning.
basically the best you can do is just pour the Freon in ( simplistically speaking)

At most, I dont think anyone overcharges or undercharges by 3 to 4 ounces which doesnt reduce efficency that much, the thing i have found is a good flush lengthy and maybe replacing the drier and expansion valve and pulling ag ood vacuum are about the best you can do.

The 300D ac system is not really that powerful compared to the other ones and when I had it once running great, it simply wasnt a bone chilling set up.

James L · #12 05-11-2007, 12:14 PM

please, people use shop air to push the flush out all the time, no shops I know use nitrogen. compressor is fine.

These cars can get 38-41 degree vent temps.

Thanks for the flippant answers carrameow and vstech!

Where did I get my R12? Plenty of R12 on ebay.

Talking with the hvac techs down at cc dickson, they think I have bad flow accross the evaporator (recommended a foam aerosol cleaner) or a bad expansion valve.

vstech · #13 05-11-2007, 12:46 PM

sorry if you think my answer was flippant. not trying to be. just warning you and others about the damage shop air can do to the internals of a system.
I would use 134a if no dry nitrogen was available. CO2 would also work.
if you have a large tank, and some good filters on your air line, the oil may not be a problem, but the moisture would be. be sure you evacuate well.
I did give some good info on the frozen lines.
sorry again if you thought my response was flippant.
John

James L · #14 05-11-2007, 04:42 PM

Sorry about the flippancy comment, being funny, as mechanics we sometimes can get opinionated. (I know I have). valid points made, however;

If you use dry nitrogen what pushes it through? shop air? The mastercool guns say use shop air, the auotzone DVD guy Bruce Bonebrake uses shop air. Anyway I had once called about nitrogen at the local welding supply and the cost for the set up/ ect. plus tank was not cost effective for my occasional use. Agree nitrogen would be choice but in the real world who uses it, knows or bothers.

At lunch around town vent temps all of a sudden changed from being stuck on 60, to 50 > with low blower setting. I took the car out on the freeway for 2 hours, 86-91 ambient outside temp and got 40-60 vent temps depending on acc/blower settings. I think I have an evaporator fin air flow/blockage issue. The back seat vent blows a little stronger. (replaced blower motor last year). I will try and use the foam cleaner in the blower case holes and see if that helps. Otherwise I may leave it alone and just monitor during the comming heat months. (My W126 may be relegated to feeway cruiser this summer and my W124 around town since it has a more up to date/stronger a/c system, especially around town). Will keep you posted and thanks.

jbaj007 · #15 05-11-2007, 10:53 PM

The dry shop air vs. nitrogen argument has always fascinated me. vstech knows more about A/C than anyone on the board so best to listen to him. He actually KNOWS A/C. But, my thoughts (such as they are).......

The molecular sieve desiccant in the new receiver/dryer will pick up about 22% of it's weight in H2O. Let's say ~ one mole or ~18 grams or cc. of liquid H2O for a R/D with ~90 grams of XH-7 or XH-9 desiccant. May not be exact numbers, but not unreasonable. Game of "Hand Grenades" close.

I think that the volume of pure H2O VAPOR for that same amount of liquid is about 22 liters. I don't think even mediocre compressed shop air could get that much water vapor in an A/C system even in Kuala Lumpur in monsoon season. That said, I've used shop air (with a filter/dryer, NO oiler... "tool air quality") for years and I vacuum down to appropriate micron levels. I have two different micron gauges. Never see a big bleed back on my gauge from H2O vaporization into the vacuum...just normal, by-the-book slight rise.. and fall on quick re-vacuum.

The BVA M.O. you used has NO, ZIP, NADA affinity for water. I've not used it personally, but it is the one the big boys on the pro MVAC and HVAC boards like. I use a little higher viscosity M.O., but I've already got it, so that's what I use with R12.

Your system doesn't know 6.7 from 6.0 oz. oil.
Your system doesn't know 2.9 lbs (46.4 oz) from 3lbs. of R12.
Your system doesn't know dry shop air from nitrogen.

New systems with R134a know small differences, but ours don't. For Heaven's sake; we measure our charge in POUNDS.

Our old A/C systems are huge by today's standards and that big R/D has a lot of volume that acts as a nice buffer for our imperfections.

Enough gab; sounds like you did everything right.

Get some dry ice at the liquor store and your big watt soldering gun. Try to "cycle" the TXV by alternating the two items above on the "hat" end of the TXV. DON'T overdo it....it's a finesse thing multiple times. Your trying to get a thin rod to free up inside the valve. If you could see inside, it looks just like a needle slide valve in a Honda motorcycle carb. (visual aide

)

Make sure the ETR bulb is in the right spot. The clear, then bubbly, then clear sight glass makes me think to check the compressor cycling. The only real cycling control we have is the ETR.

If you want to clean your evaporator; see key words by me, in the archives. Best wishes.

P.S. I can easily freeze my evaporator in 105 F ambient, so our systems can really cool with R12 (and I use a trick adjustable ETR

)