Does 60# pressure mean anything on a R12 system - PeachParts Mercedes-Benz Forum

Junkman · #1 07-26-2015, 05:44 PM

I hooked up a gauge the low side of the 85SD's AC. The system has not been converted and is not cooling. With the engine running and the compressor not engaged, there was 60# of pressure.

Wife wants AC. I want a down & dirty way to accommodate her without taking time now to learn how and implement refurbishing the entire system. Does 60# of pressure mean anything or does the system need parts replaced, then flushed, vacuumed & filled?

Only a couple of months to heater questions on the forum.

engatwork · #2 07-26-2015, 05:58 PM

First thought is that it is low on freon.

BillGrissom · #3 07-26-2015, 07:44 PM

I usually see 70 psig with engine off and pressures equalized, but could be 90 psig on a hot day (we get much hotter than TN). You should still get cooling if 60 psig, and that is certainly enough to actuate the pressure switch and engage the clutch. Does your clutch engage? If not, I think all 1985 had the infamous KLIMA relay box, so search that. You could bypass that with a manual switch or a simple relay, but leave the pressure switch in the circuit (I think Rollguy sells a conversion now). When not moving, you need the electric radiator fan to come on or you won't get much cooling. The temp sensor on the filter/drier does that and often fails or gets erratic.

If you do start fooling with refrigerant, consider HC's like Duracool or Envirosafe. They work great and are common in Europe and Canada where R-134A is outlawed (coming to the U.S.).

97 SL320 · #4 07-26-2015, 08:43 PM

Static pressure does not mean much in terms of sufficient charging. You need to engage the compressor and see what the pressures do in relationship to temperatures at the evaporator and condenser.

Also, once you get any liquid in the system , the static pressure will remain the same all the way up to the point you have the entire system filled with liquid.

There is a chart that tracks temperature Vs pressure for R12 and other refrigerants. AC pressure gauges will have this built into the scale.

cfh · #5 07-26-2015, 08:52 PM

That sounds a little low - my static pressure ('80 model W123 running R 12) is usually in the 70's in cool weather and up into the 90's in hot weather. Sounds like your system is still basically holding pressure though - some small leakage through the front seal of the R4 compressor is normal. I'd get a can of R12 plus a 2 oz can of frigi-cool oil meant for R12 (check ebay or craigslist). Also you need a good set of manifold gauges - about $30 on ebay used. Also you'll need a can tap if you're getting coolant in the small cans (instead of a 30lb jug).

Since you still have fairly good presssure there should be no need to evacuate the system or replace the drier. If you get into doing that you'll need a lot more equipment and you're probably better off taking it to an ac shop rather than buying and maintaining your own recovery machine although an R12 recovery machincan be had for surprisingly little these days).

The main thing is to make sure your cluthch is engaging and your front auxilary fan is coming on. An easy way to jump these is to pull the connections off the drier and use 20amp blade style fuses as jumpers.

Junkman · #6 07-26-2015, 09:34 PM

I'll check out the Klima and try jumping the switch on the drier. I don't remember seeing the high side port. Where is it on a 126? I may have a spare in the parts car if the part goes bad. There's also an 89 gasser in the yard not far from me.

Wars have been fought over Envirosafe (t least the verbal kind). I was hoping not to be tempted into that route. I suppose war concern is irrelevant. More have been fought over Dino.

jay_bob · #7 07-27-2015, 10:52 AM

Best thing you can do for the 80s models with the 616/617 engine is the Sanden upgrade and continue to run R12 as long as you can find it.

Don't make the mistake I did and wheeze along with a replacement R4. It is a crappy design and no amount of modern technology can cure that case of ugly.

The later 80s 126s and 124s have Denso compressors which are good.

BillGrissom · #8 07-27-2015, 03:33 PM

I wouldn't focus on the Sanden too much. I put that in my 1985 and can't say it cools any better than my 1984 w/ original R4. Both use Duracool. They are both fine at what is considered "very hot" in the east (93 F), but barely acceptable on our >100 F days. The air coming out the vents is still cool, but can't keep up with the heat load, especially if driving into the sun. Of course, worst is when sitting in traffic and the electric fan doesn't quite keep the condenser cool enough. On the highway it seems OK. I even tinted side and back windows in the 1985. I did use a Sanden "shorty" (H13), so an H15 or 508 might do better, I don't think they would fit the way I re-used the factory hoses. I suspect a parallel-flow condenser would give more bang, but is a custom design.

BillGrissom · #9 07-27-2015, 03:42 PM

Quote:

Originally Posted by Junkman

Wars have been fought over Envirosafe (t least the verbal kind)...

True, much ranting mostly from people who never tried it, and from AC shops. They even got some states to outlaw HC's. The EPA hasn't helped at all, even though HC seems the best future option. Read up on the new HO1234yc and the HF gas it produces in a fire. M-B refused to use it in cars shipped to France, lawsuits, ... Some claim HC can "explode", but impossible unless pre-mixed with air. All refrigerants (and their oils) can burn if a hose is punctured and blows on a hot turbo or exhaust, and some produce poisonous gases. 12 oz of HC is minimal mass to burn. I lit some I collected and it burned very slowly, similar to a wax candle. It can only burn as fast as the cold liquid gets vaporized. Fear carrying a newspaper in the car more.

engatwork · #10 07-27-2015, 05:41 PM

Quote:

but impossible unless pre-mixed with air.

Like in a leak?

Not to get off on a tangent but here is some good reading:

MB new freon

Phil · #11 07-27-2015, 08:00 PM

I think I would start by figuring out if the compressor is getting power to the clutch and if not why not. 60 psi is probably enough to keep from tripping any low pressure safety switch so what is keeping it from pulling in the clutch? Is it the CCU or a relay or what?

dieselgirl85300D · #12 07-27-2015, 09:06 PM

I have that chart but the forum wont let me load it
I think its in vstech long a/c thread

rrgrassi · #13 07-28-2015, 11:20 AM

what is the pressure on the high side? 60 psi seems low, but at least there is some pressure. Check the #8 fuse. It kept blowing on my car, so I separated the fan system and used a relay. That stopped that problem, but the #8 area in the panel was already melted away. Other fuse kept blowing, when driving, turned out to be a bad connection at the compressor for me.

compress ignite · #14 08-05-2015, 04:32 PM

GPS

leathermang · #15 08-05-2015, 06:40 PM

Quote:

Originally Posted by BillGrissom

If you do start fooling with refrigerant, consider HC's like Duracool or Envirosafe. They work great and are common in Europe and Canada where R-134A is outlawed (coming to the U.S.).

Bill is excellent at misdirection and slight of concepts.
Describing something true...like that most refrigerants mixed with oil and sprayed on hot exhaust will ignite......
If you mix something like Propane with oil mixed it WILL catch on fire.. and the idea that the amount would be a ' little fire' ... amazing....
IF you are in an accident ... perhaps with family in the car... I say any UNNECESSARY extra risk of fire is poor planning.
Below is some of the EPA , including the 19 states which ban HC's in mobile ...notice MOBILE.... AC systems.... because stationary ones... at buildings... do not go down the road subject to random collisions...

from the EPA site...
""""May hydrocarbon refrigerants be vented?
No. Since November 15, 1995, the Clean Air Act has prohibited the venting of any refrigerant during the service, maintenance, repair, or disposal of air conditioning and refrigeration systems. When working on a system containing a hydrocarbon refrigerant such as HC-12a® or DURACOOL 12a®, the technician must recover the refrigerant into a suitable container and safely dispose of it.
What other regulations restrict the use and handling of hydrocarbon refrigerants?
In addition to the prohibition on use described above, and the federal law banning the venting of all refrigerants, there are also state and local statutes and regulations that relate to certain uses of hydrocarbons. As of the printing date of this fact sheet, EPA is aware that the following states prohibit the use of flammable refrigerants in automobile air conditioners: Arkansas, Arizona, Connecticut, Florida, Idaho, Iowa, Indiana, Kansas, Louisiana, Maryland, Nebraska, North Dakota, Oklahoma, Texas, Utah, Virginia, Washington, Wisconsin, and the District of Columbia.

Local fire codes also often restrict the storage of flammable materials. In addition, other federal, state, and local regulatory agencies may have regulations related to flammable refrigerants. Check with these authorities for more information.""""

Somehow some way Bill has some financial interest in selling Duracool... holds stocks, a relative works for the company.... there has to be some reason he would go to the trouble to try to mislead people year after year.