My turn for the Evaporator Party - Page 3 - PeachParts Mercedes-Benz Forum

david s poole · #31 02-28-2007, 06:15 PM

if you convert to 134a you will have about 70% of the efficiency that you had with r12.the cooling should be fine until the ambient temp goes above 94f then the condensing requirement of 134a goes off the scale.to convert properly you need to oversize all components by at least 50% and fit the barrier hose so that you wont need to fill the system every year.good luck finding a condensor with the required capacity.stick with r12,it's a much better refrigerant.

davidmash · #32 02-28-2007, 07:38 PM

Thanks for the info. I guess the man thing I am concerned about is long term. I am planning on driving the car till the wheels fall off or I go broke. Which come first at this point is still somewhat of a debate. The car may cause me to go broke but I guess that belongs in another thread.

Anyway, I am concerned about R12 either going away entirely or being so bloody expensive that it is not worth. The argument being used for the conversion is that since I have to have it all replaced anyway (coil, dryer…. Etc) why not do the conversion now rather than maybe having to do it somewhere down line. If another component fails and I loose the R12 I have to get more.

Last summer, the car kept me comfortable in the TX heat. If I switch to R134 and I am not cool, I will be pissed and there will be a good chance that some crazy SOB on the freeway will piss me off and get shot in the process (I do not tolerate pin heads on the freeway very well…. Anger issues I guess) and then I go to jail, become someone's b!tch, loose the car, the wife, house, 5 cats and 1 dog, you see where this is going right? Ah, decisions? I guess I will make an appointment at the indi and pick their brain while they are giving me an est.

One more question. I thought I read here (forgot what thread) that the coil on a 190 can be accessed through the firewall, the indi said he did not think it could be. I have the shop manual at home (have not looked at it yet), does anyone know the answer? Will it say in the shop manual?

Thanks for all the input.

#33 03-01-2007, 07:59 AM

As others here, I am NOT a fan of converting to 134. I live in Texas, so all the capacity I can get is needed.

R12 is getting LESS expensive, not MORE! The vehicles that require it are at an age that they are hitting the wrecking yards in record numbers, thus the demand is decreasing. You know, supply and demand determining the prices?

I bought a 30 pound bottle of R12 from Refrigerant Supply in Colorado two years ago for, I think, about $400. At that same time 134 was going up in price. I expect that you could buy a 30 pound bottle now for less than $400. Check it out.

You will need a 609 license, but you can take an online, open book test for $15 in less than a couple of hours.

Good luck,

E150GT · #34 03-01-2007, 08:37 AM

A mechanic said to me that when r134a first came out it was less efficient in original r12 cars. He had wanted to convert my 420sel but I respectfully refused. I told him that I wanted a/c that was cold not cool. He told me that the r134a that is made now is more efficient in cooling and that he could make a conversion now that would be just or almost as cold as r12. He said that maybe two years ago the coversion would leave customers unhappy.

#35 03-01-2007, 08:58 AM

E150GT,

I respectfully suggest that your mechanic is FULL OF IT! Saying that 134 has changed is like saying that the law of gravity has changed such that water will now pour up hill.

I expect that if you took him up on it, he would put one of the junk coolants in the system behind your back and tell you that it is 134. Find a new mechanic.

david s poole · #36 03-01-2007, 09:55 AM

agreed,the formula for 134a has not changed.refrigerants work because of the heat required to change state from liquid to gas.no magic just pure physics.heat is measured in btu's and 1lb of 134a will require 30% less heat to change from liquid to gas than will 1lb of r12.the only way to make 134a do as much work as r12 is to make the components about 50% larger and or more efficient.

jcyuhn · #37 03-01-2007, 10:23 AM

Hi All -

I've been there, done that. During the winter of 2003 I replaced the entire a/c system of my 1987 300TD wagon. Evap, condenser, compressor, manifold hoses, etc. Just got tired of chasing leaks every year and decided to fix it right.

I used a synthetic refrigerant oil compatible with both R-134a and R-12. I initially charged the car with R-134a. Given the price of R-12 I wanted to be certain there were no slow leaks.

I drove it that way until about the end of July. And I live in Dallas. Surprisingly, the R-134a did an acceptable job of cooling. I recovered the R-134a and changed to R-12 more out of curiosity than any lack of comfort. At the time I posted a writeup with a comparison of vent temps and such, it can likely be found via a search. As I recall there was little or no difference in the final vent temp produced by each refrigerant. But the R-12 seemed to cool down faster - the air was noticably cold by the end of the driveway, as opposed to half-way down the block.

My theory is the lack of cooling has as much to do with the dirty/bent/broken fins on the evaporater and condenser reducing the heat transfer ability of each as to any inherent differences between R-12 and R-134a. With fresh parts the R-134a worked OK.

- JimY

brewtoo · #38 03-01-2007, 12:05 PM

Quote:

Originally Posted by david s poole

heat is measured in btu's and 1lb of 134a will require 30% less heat to change from liquid to gas than will 1lb of r12.the only way to make 134a do as much work as r12 is to make the components about 50% larger and or more efficient.

Good and interesting point which makes me wonder...when you do a conversion, why do you put in LESS 134a than you would if you were still using r12?

david s poole · #39 03-01-2007, 12:11 PM

you put in less because it requires less heat to go from liquid to gas and therefore find an equilibrium.

#40 03-01-2007, 12:52 PM

Yes if you are charging with 134 by weight in a converted system, you put in .85 times the specified R12 amount. If you are topping off a system, however, it gets more touchy than that. Even when charging an empty, converted system by weight there can be a little black magic involved in getting the charge right.

What I call "black magic" is probably the "equilibrium" as David more correctly puts it.

davidmash · #41 03-01-2007, 05:40 PM

Man, this keeps getting more and more difficult.

Given the current discussion I am leaning toward staying with R12. I do not want to risk loosing efficiency on my system. The temps in Dallas are too extreme for me to risk it.

Given that most of the system will be replaced, are their any incidentals that should be replaced as well. I would like to just have this done one time.

Some mentioned the O-rings, and someone else mentioned the low pressure hose. What else? Can/should a compressor be overhauled or maintained? The condenser (in front of the radiator) is only about 4 years old.

thanks

jcyuhn · #42 03-01-2007, 06:17 PM

Ah, don't interpret my post as encouraging you to use R-134a, that's not the intent. I wanted to point out that performance perhaps does not suffer as much as one would be led to believe based on postings here. The cost difference between the two refrigerants is insignificant in the context of all the other work, so use the good stuff!

As for what to replace. The basics are evaporater, expansion valve, and dryer. If the car has the original manifold hoses (to/from the compressor) it's probably time for those as well. (Some shops can rebuild these, saving you a ton 'o dough.) O-rings are good, they are a prime source of leaks when they get old and brittle, say after 20 years of service. There are also two electrical switches which thread into the dryer, they have been known to leak on an occasion or two.

Compressors are expensive; I'd only replace if it's original or if there are obvious problems - funny noises or leaks.

If the condenser is 4 years old, it can stay. That's practically brand new as far as this car is concerned.

- JimY

#43 03-02-2007, 07:24 AM

Quote:

Originally Posted by jcyuhn

Ah, don't interpret my post as encouraging you to use R-134a, that's not the intent. I wanted to point out that performance perhaps does not suffer as much as one would be led to believe based on postings here. The cost difference between the two refrigerants is insignificant in the context of all the other work, so use the good stuff!

As for what to replace. The basics are evaporater, expansion valve, and dryer. If the car has the original manifold hoses (to/from the compressor) it's probably time for those as well. (Some shops can rebuild these, saving you a ton 'o dough.) O-rings are good, they are a prime source of leaks when they get old and brittle, say after 20 years of service. There are also two electrical switches which thread into the dryer, they have been known to leak on an occasion or two.

Compressors are expensive; I'd only replace if it's original or if there are obvious problems - funny noises or leaks.

If the condenser is 4 years old, it can stay. That's practically brand new as far as this car is concerned.

- JimY

See the text in bold above. THAT is a statement of wisdom.

Since you are in Dallas, the best automotive a/c place I've ever dealt with is McCains in Richardson near the Floyd Rd. TI Plant. Their address is on Floyd Circle. Mark McCain will give you advice. Sell you what you need and not try to sell you something that you don't. They also do a/c work and are good and honest.

Good luck,

david s poole · #44 03-02-2007, 10:08 AM

if you are going to use 134a,take out the condensor,block the pipes from moisture,get some of the strong acid used to clean mag wheels and spray it on the condensor and remove the black paint until the pipes shine.this will aid your condensing by approx 40%[the big prob with 134 is condensing]

#45 03-02-2007, 10:36 AM

Yes, condensor capacity is key. I did not know though that removing the black paint would help so much. That sounds like a GREAT alternative to fitting parallel flow condensor.