A cheaper more primitive a/c system - PeachParts Mercedes-Benz Forum

netboy · #1 08-04-2010, 08:15 AM

I have an '83 300sd that i bought for $300. It runs great, 80 mph, 30 mpg, on WVO. I use it to commute about 4hrs each week. The a/c compressor is shot and I don't want to spend more money than I paid for the car to fix it.
This is the plan:

Remove compressor for weight and remove condenser to alow better engine cooling.
Fill a cooler full of ice water in the front floor board, submerge a 12vdc marine bilge pump($16) into the water and pump water thru my evaporator and back into the cooler. The fan blowing across the evap should cool the car down. Does anyone see a problem with my plan?

I figure I can buy alot of ice for what a complete a/c sys. fix would cost.

I need to know where the best place to tap into the system for the in and out ports of the evaporator. Would it be at the exp. valve? If so which ports?

compu_85 · #2 08-04-2010, 08:27 AM

I'd at least try to find out what's wrong with the system first. It could be a simple fix!

-Jason

Junkman · #3 08-04-2010, 08:50 AM

You're going around the world for nothing. Cheap $16 bildge pumps aren't meant to run continuously so that is $16 thrown in the trash.

A really cheap air conditioning system is the 460 which came standard on all Mercedes diesels - ie 4 windows down, 60 mph.

Take the money you saved on the car & fix your AC. Or...take your time researching and you won't need AC because it will be winter. Perhaps begin with the heater threads to move ahead of the curve.

JEBalles · #4 08-04-2010, 09:10 AM

Yeah, A/C work really isn't that hard or expensive (if you do it yourself) and you should be able to find a compressor in the junkyard for pretty cheap. I actually have a spare compressor, I just don't know if it works.

thayer · #5 08-04-2010, 09:17 AM

If the A/C system holds 150 psi, and you are getting 12 volts to the compressor and your blower is blowing, then you can fix it awesome for about what you paid for it.

get a NEW compressor (150$ at Mcparts online after 50$ off) if fastlane is moving compressors now, feel free to delete. I couldn't find any when I searched.

Get a reciever dryer (20$)

Have your indy ac guy install compressor purge with nitrogen, install dryer with oil, pull vacuum. 3.3lbs of r12 (or 2.8ish lbs of 134) and fire it up.

AC guys (vstech specifically as everything I know about ac I'm pretty sure he taught me) feel free to complete what I am missing.

netboy · #6 08-04-2010, 10:00 AM

I should have stated previously that the compressor is shot. Jumpered the pressure switch and the clutch does not engage.
(so that is whats wrong with the system, its not a simple fix)

Junkman, actually bilge pumps are made to run continous, ask anybody who knows anything about boats. The are made to pump rain water out of a boat all night long. Or until the batt runs down! So 4hrs of running should be a breeze for a pump.

Thayer, I have just rebuilt the a/c system on my son's '81 300sd for $350 for compressor, rec/dry,exp valve, and 609 cert. Its r12 and its cold.

I also restored my daughter's '85 300d, which is 134 and not near as cold.

I spent a day of my life and $60 on refridge restoring a sys with a used compressor that ran for about 10 minutes, so the one thing I know about a/c systems is ....NEVER INSTALL A USED COMPRESSOR!!!!!!!

I am going to try it, my main concern is the evap was made for gas and I'm pumping water thru it.....may be a problem.

Is the exp valve the best place to tap into the lines for IN and OUT of evap? Anyone

TX76513 · #7 08-04-2010, 10:18 AM

Your project is interesting and it would work but I believe there is one problem you are overlooking. The simple law of energy A consequence of this law is that energy can neither be created nor destroyed, it can only be transformed from one state to another and you can't get more energy out of something that wasn't there to begin with.

You are probably looking at 20 pounds of ice per hour to make this work effectively.

mach0415 · #8 08-04-2010, 10:42 AM

Don't take this personally, but I hear the theme to Sanford and Son playing...

rrgrassi · #9 08-04-2010, 10:51 AM

What would be neat is if we could drop in a totally electric system, like a household set up. I know we would need to have a beefier alternator, etc.

I wonder if they even make a 12 volt compressors that would work?

DocSarvis · #10 08-04-2010, 11:02 AM

You seem to be an expert with all the systems you have "restored" but. A clutch not engaging does not mean the compressor is shot but thats ok. Energy transfer/time/ and available energy in ice is the problem with your proposed system. Hint, AC systems are rated in tons. Tons of ice and the energy required to melt a ton of ice. Next hint heat transfer takes time. Your proposal to blow warm air over a "luke cool" say 40 degrees evaparator will net you maybe a degree in cooling. so you take 90 degree air and cool it to 89 degrees. But that is an improvement. With that said.....go for it. If I'm wrong and the laws of thermodynamics have changed you may hit it big. Start working on the heater. Thanks

rrgrassi · #11 08-04-2010, 11:07 AM

I was looking at a 1930's era Dodge that had "A/C" It had the air scoop in front, by the windshield, and in the cabin, was a dry ice compartment, that the air flow was directed over. Neat innovation, but I do not see how that would last very long, and the car had to be moving to get air flow, since there was no fan.

TX76513 · #12 08-04-2010, 11:25 AM

Quote:

Originally Posted by rrgrassi

What would be neat is if we could drop in a totally electric system, like a household set up. I know we would need to have a beefier alternator, etc.

I wonder if they even make a 12 volt compressors that would work?

Yes, we use them on our electric buses.

thayer · #13 08-04-2010, 11:37 AM

Hey, if you are that into it....TAKE PICTURES. The Expansion valve is the "in" to the evap. Not sure where the return is. If this works, I will be impressed.

They may be other methods besides ice to fuel coldness into the evap. Dry ice like the above mentioned. there is also a chance you could dissassemble a dorm size refridgerator with a beefy alternator to supply coldness, maybe even power it by the use of a constantly charging battery and an amp style capacitor for initial fire up.

http://www.certifiedmastertech.com/wordpress/wp-content/uploads/2009/03/automobile-air-conditioning-diagram-233x300.jpg

according to that pic, follow the low side back into the dash and you will find your "out"

netboy · #14 08-04-2010, 11:47 AM

"Great spirits have always encounter violent opposition from mediocre minds"

This is not the first time Ive been called Fred Sanford. I think about it when I'm cruising down 75 South @ 85mph in a $300 Benz burning straight gease that I collect and filter in my garage....

I'm not creating or destroying energy....I'm changing a solid to a liquid in a 4 hr time span. I took Physics also.

An EXPERT.... Thanks for the complement...

Tons of Ice? Really, Ever took a cooler camping? 2 bags of ice stay cold for 2 days. Now I know blowing air over the cold water will speed up the process and so I may need 4 bags.

Whether you think it will work doesn't matter, I'm doing it. Just need to know if anyone knows the shortest route in and out of the evaporator....ANYONE? any free thinkers?

rrgrassi · #15 08-04-2010, 12:09 PM

You will have to do some line cutting to get the the evaporator, or use the fittings where the exp valve is.