Automotive AC question

Got a mercedes 240d 81 year with r12 ac system. Anyways, from as long as my dad owned it in 90 something it blows hot air at idle and takes a few minutes at half throttle to make cool air. It never really has gotten cold and that was blamed on Germans not making good ac systems. THe best time it works is at night at about 70 degrees outside

Its been serviced, switched from r12 to 134a and back to r12.

Anyway, it still does not make cold air and always smell a sweet smell in the car. It was checked a few weeks ago by a place that does not do ac service and they said it was ok.

I have ordered some freeze 12 and sealer off the internet to put in the system to give it a try, assuming the system is low.

I believe from my reading the system works like this. Compressor makes the gas hot and high pressure, condinser makes it cooler and a liquid, this liquid goes into the accumulator/receiver dryer and pools as it goes into the oricice or expansive valve into teh evaporator in the car making cold air. If the freon pools in the accumulator/dryer it triggers a sensor to turn off the compressor to keep it from sending liquid to the compressor causing damage, right?

Then the gas goes from the passenger compartment back to the compressor to be recompressed.

I am only to assume that it only cycles the compressor at night in 70 degree weather that its "low" on freon.

I got a kit and going to hook up the basic meter to it and check the site glass this weekend. I was wondering if anyone had any opinions or experience with this? I would love to get the ac to work at idle and can either assume its either low on freon, compressor doesnt spin fast enough to make enough pressure or its just a poorly designed ac system from the start.

Check if when you turn the ac on, the condenser fan running. If the fan run the same when the ac on and off, then the fan clutch is bad.

I've owned 3 of the 123 body MBZs. My guess is that your auxiliary (electric) cooling fan is not operating. Its probably the sensor which tells the fan when to operate. It's located next to the dryer, which is behind the radiator on the passenger side (near the sight glass).

They are actually quite good a/c systems.

Go here www.performanceproducts4benz.com ...the last one to the gas pump is the winner!!!

Hey... switching from R12 to R134a is problematic, and you mentioned that it's been switched again to R12... well this leads me to believe the whole system should be flushed and the compressor and receiver be replaced.

This is why: The lubricants in R12 and R134a are not compatible. If either refrigerant mixes with the other's lubricant, the lubricant turns to slurry that clogs up the system. It's a total nightmare. The lines, condenser and heat exchanger can be flushed, but the receiver and compressor are considered unflushable.

Alternatively, you can rebuild the compressor yourself, it's not that difficult if you have the manual. You'll need a pulley remover to do it and a clean workbench so you don't accidentally contaminate the seals with dust. Nothing worse that rebuilding a compressor and having it leak refrigerant as soon as you start filling it!

The upside of this is that you can choose a refrigerant and stick with it. You'll know the history of the system, for all intents and purposes.

Before you get that far, go ahead with the other suggestions... they're basically free. You can get an a/c manifold pressure gauge too, to make sure you don't have low system pressure on the low side, which would indicate low refrigerant/leaky seals. If you "gas it up" and the pressure goes low again, it's a leaky seal or hose. If you have low pressure on the high side, probably a bad compressor. If you have very high pressure on the high side, probably clogged system.

Good Luck!!

cobb said:

Got a mercedes 240d 81 year with r12 ac system. Anyways, from as long as my dad owned it in 90 something it blows hot air at idle and takes a few minutes at half throttle to make cool air. It never really has gotten cold and that was blamed on Germans not making good ac systems. THe best time it works is at night at about 70 degrees outside

Its been serviced, switched from r12 to 134a and back to r12.

Click to expand...

That scares me. This requires the dryer be replaced, compressor oil flushed out and etc. If the dryer is not compatible, it can clog up the system.

Dad told me it over heated and blew a compressor cause the aux electric fan didnt turn on. It has a direct drive fan too. I used a paper clip to over ride the sensor to make the fan stay on. It still seems to run warm and the ac only improved slightly. Changing thermostat and antifreeze this weekend and oil and filter.

I am guessing since it seldoms cycles its low on freon?

No rust, could use a paint job. I was told that a car wrap is cheaper than paint, may try it. Takes 94 seconds to go from 0-60, max speed 70.

A guy at my other job who was a mercedes fan said he use to put a gallon of gas in with a tank of diesel and how it made more power. THe mechanics at the truck place I work said I need a back pressure test and too much back pressure is likely causing the lack of power.

EDITED, when the compressor was replaced, it was retrofitted for 134a. New dryer and other stuff. He took it to a back yard mercedes expert who recharged it with r12 when he did some work on the rear end and axle shafts. He didnt want it done to the ac and the guy just dropped off the face of the earth.

I asked the guys at work, they say r12 oil and 134 a dont mix, compressor starves from lack of oil. However the reverse is ok.

I have a 134a kit, but need to get someone qualified to suck out the rest of the r12 in the system. I hoped maybe just using the freeze r12 aftermarket freon with the existing r12 would do it. I hate to spend too much money on this asits been like this for some time and the damage already done.

Of course, I wont know til I hook up the guage. I am assuming the guage will work on either system. Its one of those screw ons that reads the psi on the low side and has a section for low, ok and high.

The AC has been poor ever since my dad owned it in the mid 90s, so it maybe a leak somewhere causing it to loose the optimun amount of freon or it is just poorly made.

I am rather disappointed in the low speed of the fan and if I had my way, I would install the largest diameter electric fan on the thing and hook it to a relay with the ac one. At idle the ac blows hot and the car will over heat if unchecked.

One strange thing is that it runs almost in the red zone on the innerstate, however when taking an off ramp down to 35 mph the temp rapidly cools a mark on the guage. I can either assume its running harder and hotter than the capacity of the radiator, turburlance under the car blocks the air flow or something with the thermostat not opening all the way.

Based on that history, the compressor and dryer are probably FUBARed. I'd plan on replacement. If you do, don't even consider R12.

Secondly, the 240 is slow, but it shouldn't be that slow and it shouldn't heat like that at highway speeds. Just too many possibilities to try to deal with here. Anywhere from head gasket to injector pump timeing/advance to cam chain and so on. The mpg you report is about right, so that makes it even more puzzling.

Any city will have a several independent garages that specialize in MBZ's or European cars. I'd probably bite the bullet and talk to one of them. I imagine most would be able to advise you at little or no charge. I would not go to a dealer.

As much as I like these older MBZ's, unless you're a capable doityourself wrench, their market value makes major repairs not too practical.

sounds like a bunch of idiots with deathkits have been working on your ac.
a proper retrofit does NOT come in a kit at the local big box store .
and if there is a mix of 12/134 in it nobody will want it in their recovery system.the other way of getting rid of the charge is illegal...dont get caught venting it.
you will need a reciever/dryer,and at least a drain of all old oil along with a flush to get it right.
i bet the poor performance is due to the orifice tube filter being plugged up with snot from incompatible oils.
better get a book about basic ac service and a manifold before you go any further.

And since the fittings for R12/R134 are incompatible, I'm wondering if the guy really added R12 to the R134. He would have to have made several changes to his equipment to do that.

If the R134 fittings are still in place, you can have it vacuumd at a garage and replace with new R134. Should take about 2 1/2 cans at $10-12 per can. You can get a simple refill hose for $10 at parts store and fill it yourself. At least that'll give you a starting place - you'll know if there actually was a mix of gases.

But, I think the engine heating/performance problem far overshadows your a/c problem. I'd drive with the windows down til I solved that.

And you've got a lot of folks blowing smoke, such as adding gasoline to the diesel -- just ain't a good thing to do. Find someone who really knows what to do with these cars -- they're tough and will run forever with reasonable care but they will break and wear just like anything else.

Snakebite makes a good point. If you take it to be vacuumed, tell the garage that you suspect a mix of gases. It would be uncool to let them unknowingly add the mix to one of their regular tanks. Most will have a "junk" tank that they vacuum questionable gases into.

Do you guys know how to tell r134 a from r12 in a system, other than looking at the sticker or fittings? I am going to assume it still has the r134a fittings as they look right to attach to a r134a kit I have to top off 134a systems. I believe 99% that the mercedes dealer converter it to 134a with a it they offered when the compresor and receiver dryer was replaced. It does have a faded mercedes sticker under the hood about the ac system.

Is there much more harm in adding r134 a to the system since its been converted and may have some r12 in it?

I may have a buyer for the car and just need it to work for another month or so while i drive it. Today it was non existant and I ended up using the 4 55 method to stay cool. Of course the temp meter still happlied climed up to the danger zone as I was running around to get oil, anti freeze and thermostat for it.

I saw a r134a kit for 40 bucks at an auto store and it was tempting to buy it and filler up. I think my folks have a few cans at there house from the tools left by a family member who died a few years ago. I will make sure to use a can of the stop leak stuff too.

Beats me how my dad drove the car. It really lacks throttle response and torque. It doesnt smoke and does not seem to leak. I have the tires fully inflated trying to give it less rolling resistance.

Oh, well, used vehicle #2. Next car, maybe very soon will be new, with warranty, possibility an automatic tranny, cold, cold ac and upwards to 40mpg.

Your 134 hose won't fit r12 fittings. Didn't you write that you have a simple gauge? What does it indicate? If it's showing at or near the top of the green, it would do no good to add and would/could cause damage.

I thought of one thing re: performance. change the fuel filters. It has a small secondary near the injector pump and a large canister type at the front drivers side of the engine. A fouled filter will really cause decreased performance. One 300D I had (an 81 also) went overnight from an easy 75-80 cruise to barely 65. Nothing but the filter.

Filter will probably do nothing for the heating problem. You'll just have to work thru that starting simple. The thermostat is a good start but first check or replace THE RAIDATOR CAP!!!! (obviously, i have this thing about radiator caps) I once totally rebuilt a 7.3 Ford cooling system, many $$$ and hours, to finally figure out it was merely a bad cap.

The car has r134a fittings as it was converted, spoke to Dad earlier the former owner of the car. It was converter at the benz dealer when the compressor was replaced and the other crap associated with a conversion. Still it blew hot air at idle.

Anyway, the ac tools are at my folks house, 57 miles from here and lots is speculation. The r134a kit I briefly saw had what looked like a tire pressure meter that screwed onto the low side to give you a psi and a color coded range. I am going to assume by using the hand test on the receiver that its low on freon. Maybe the psi on the low side is in the same range for either r12 or 134 a for their condition, assuming it was replaced with r12 from 134a.

I also believe I have some cans of r134a with several kits that I inherited and the necessary can taps and plumbing for freon for 134a systems. I have two cans of freeze 12 on order and had planned to use the hardware from the r134a kits to charge it up. If its extreamily low, I may just use the r134a instead.

Spoke to dad tonight regarding fuel filters. Said it uses a spin on and a plastic one with a total cost of 15 bucks. Going to buy both tomorrow and 170 degree thermostat. Believe it has an 80 c one or 176 degree F in it. Going to mix 50-50 antifreeze and flush it. I believe the radiator cap is ok.

I did manage to chirp the tires in 2nd gear once today in stop and go traffic. I wasnt able to launch it in first gear like I could a few weeks ago. Just amazing how you can push the petal to the floor and slowly it revs up. I would say ten seconds from flooring it before it revs in the upper band and starts to make a good noise that makes you back off the petal. Seems to rev at the same speed in first gear.

Good plan.

Edit -- Don't forget to bleed air from the top of the primary filter and prime the system by using the priming pump located at the secondary filter.

Haynes manual is very good. May be in your public library.

And living in a van by the river sounds pretty good to me some times.

While at the auto store getting the filters and what not, came across the freon isle. Man, so much to choose from. I was very tempted by a sealant kit for metal and seals in r134a only systems and a can of freon for 134a systems that was formulated by nasa and used by the military to make cold air quicker in stop and go traffic by 50% more.

Of course, I hate to use the sealer stuff if it will clog up anything, sure looks like the stock receiver dryer with sight guage on it. It was rather small and I couldnt tell if it was a dot or a real glass window.

The nasa freon was very tempting since it stated to be 50% better. The parts guy spoke highly of it and said a can is what they use in an suv, so I could use half a can at the most.

No word from the website about the freeze12 I bought, may of been a poorly managed site or they jsut took my money.

Going to the folks house to get dads help with the filters and what not. He seems to know a lot about the car, but nothing about the adjuster on the dashboard for the idle. I am thinking about cranking it up so my lights do not dim at idle with the ac on. I think the book said something about it used for cold starting.

Your right about the idle adjustment -- it's a simple hand throttle for cold starts. No reason not to adjust your idle faster.

However the slow idle makes me wonder if you have injector pump timing issues. That could be the root of your performance problems.

I know nothing about the "freeze 12", but it sounds as if it might be an r12 product. I would not use it with r134 or you'll be mixing the gases.

I suggest you use the regular 134, at least until you figure out the cause of your a'c problems.

One other thing I thought of -- you verified that the aux fan functions by jumping the sensor connector. Have you checked it, while hot idleing with the a/c on to see if the sensor is activating it. I had to replace a sensor in my 81.

If you want to, pm me your email and we'll take this off the forum and save space.

edit - whether it's an suv or mbz makes little difference in the capacity of the a/c system. they're all about the same

I bit the bullet after hearing the news of hot weather lately and the lack of repsonse from the company I ordered the replacement r12 from online, so I bought a bottle of 134a from the local parts store. It came with a trigger button and meter to read the system psi/condition. I believe it was made by ida and this tall can advertises to be 50% cooler than regular 134a and used by the military.

My system read 0-5 psi when I hooked it up with the car running and ac running. I charged it til it was in the blue area or 35-45psi. I also use a sealer kit that has 2 cans, part 1 and part 2. Part 2 was never installed as it blew all over the place when I went to install it. Since the can of 134a comes with sealer, leak detector, I let it go.

Immediately it was colder blowing and got sweat on the low side hose. An indication from some online reading it was charged. I let it running 30 minutes from refill and left it idling at the side of a gas station. Imaging how cold the insde of the car was.

Everything was cold, door, interior, keys, seat, steering wheel, etc. Unbelievable. Started to develop frost on the outside of the lower part of the windshield and some on the side windows.

Either the system is loosing 10psi a day used or there is some adjustment in the 134 a in the system after charged and used.

Blew cold today at almost 100 degrees after startup. No revving needed this afternoon.

ALso bought some filters for fuel, oil and oil change, antifreeze, thermostat, etc. One of the fuel filters was clear and you can see it was clogged. Throttle response is better, but still underpowered. I think maybe got a 5% increase in power. Sounds quieter after oil and filter change. Still ran on the warm side this afternoon. Maybe having a fully function ac system dumps more heat into the radaitor than ever?

After reading online about freon, charging, etc, I decided a lot of it was theory more so than fact. Seems it illegal for a licensed person to mix freon, but it will still work.

Seems the biggest truthful claim is that change of freon may not circulate the oil in the system and cause it to die. Not sure the auto service shop installs oil and a sealer like the premixed cans do. I think they do include a leak detector dye. I know before hand what little poofed out was dry before hand, now its greasy when it poofs when you connect or disconnect it.

Sure you should draw a vacuum to remove moisture, assuming there is any in there and the received dryer decides to quit. If moisture is in the system, it will blow cold then stop after a few minutes. Also according to online info moisture can cause the inside of the system to corrode. How with oil too in the system beats me.

Cobb,

Can you list the specific items that you purchased? Last time I was in auto-parts store, there were just too many A/C related gizmos. If you can list the brand name, that would help.

Thanks,
- Vikas

Cobb
Glad to know that you fix it.

It still works and is holding at 45psi on the low side when I went to check it yesterday afternoon, late evening.

Strange to hear the compressor cycle off and on, something that never happened before.

When a system is convered from r12 to 134 a the sight glass if on the new receiver/dryer is useless, or so I read. One way to tell the system capacity is to feel the temp of both hoses to and from the receiver/dryer.

If both are the same warm/hot temp, its full. If the one from the condensor, the radiator part is colder than the one going into the fire wall its under charged and needs more. If the one from the radiator is colder than the one to the fire wall than its over charged.

Sorry for not listing it, I see it can be confusing with all they sell. I bought another can to have on hand and a can of matching sealer. They no longer sell the two part sealer kit I bought that was in a blister pack.

http://www.autobarn.net/intaf1.html artic freeze with trigger button and meter.

I think anyone with an r134a system that is not performing too well should buy a can. It will tell you with the engine running and ac on full blast rather its filled, low or high and if low, you can pull the trigger and fill it up. It inclused oil, sealer and leak detector dye. Just make sure to hook it to the low side to beek from anything blowing up in your hand.