201 A/C doesn't work unless at highway speed - PeachParts Mercedes-Benz Forum

brookspw · #1 05-14-2004, 11:52 AM

Not exactly breaking new ground here with the knowledge that the 201 has an undersized AC. Mine is a 1991 190E 2.6.

Bought the car 3 years ago. Never had any AC work or problems from the original owner.

AC was adequate the first year, last summer was a little weaker, and this year it is much less effective. On hot days, I only get sufficient cooling when at consistent highway speeds, or at least going 40-50 mph with no stop and go.

I don't have bubbles/clouding in the freon bubble window. I have all records and do not see where in its 13 years of operation that any freon has ever been added/topped off.

To complicate matters, I do know that my auxiliary water pump (the one near the firewall at the back of the engine that circulates what into the heater core) is weak and needs eventual replacing. That does reduce my heater operation while at an extended stop. I don't suppose that should have any effect on my AC, though, should it.

Questions:

What do you expect the problem is?
What should it cost to get it fixed?
I don't want to convert to 134.

Thanks to all in advance.

Eric Eliel · #2 05-14-2004, 12:33 PM

Start from scratch. 13 year old car losing 1/8 pound per year and you are already at 1/2 capacity. PLUS you have lost the same amount of system oil (less lubriacation for the pump).

1) Buy a digital pencil thermometer from Harbor Freight for $6. You should get 40 to 44 degrees at highway speed at the center vent after the system has been running.

2) Get the car in to your mechanic, put a set of gauges on it and start there. Its probably low because of a leak.

3) Find the leak and repair.

4) Refill with more oil AND more refridgerant.

Doesn't sound like you have mcuh experience with a/c, perhaps this is something you ought to have done. Home DIY can do more damage to a/c systems than repairs if they haven't done lots of extensive research. PLEASE find a good a/c person. If the system needs a charge AND the tech doesn't add any oil to the system, I'd be careful.

brookspw · #3 05-14-2004, 01:22 PM

You are right in your assessment that I am not an A/C expert. I am quite handy mechanically and do most of my own work. This, however, is out of not only my ability level but my understanding level as well.

Please clarify: It appears that you are saying that through normal usage you lose 1/8 pound per year. Then you say that mine is due to a leak. When you say "leak", do you mean that which normally exists and seeps out or a "leak" that must be repaired? Or, do you mean both?

In such a repair, do I just lose the R12 that is in there now?

Thanks

md21722 · #4 05-14-2004, 01:32 PM

To repair a leak you'll lose all your R-12 beacuse the system will open up. You'll also need to pull vacuum on the system for a while using a vac pump designed for A/C systems. You should also consider replacing the drier at this time since its old and they don't last forever.

First step is to find out where its leaking from...

Regards,

brookspw · #5 05-14-2004, 01:39 PM

Quote:

Originally posted by md21722
To repair a leak you'll lose all your R-12 beacuse the system will open up. You'll also need to pull vacuum on the system for a while using a vac pump designed for A/C systems. You should also consider replacing the drier at this time since its old and they don't last forever.

First step is to find out where its leaking from...

Regards,

When they pull/capture the r12 I have now, it can't be reused?

Tobias MB · #6 05-14-2004, 01:58 PM

The reason, IF, you say there are no bubbles showing in the sight glass, is because the auxiliary fan in front of the radiator is not functioning and is needed at slower operating speeds. Check to see if it operates, if not, then:

This can happen due to a blown fuse, a defective AC relay, engine temperature sensor or a bad pressure switch on top of your AC drier. To check the drier switch pull the two wires from the pigtails on the sensor on the top/side of the drier and short them out, hence bypassing the switch. If the fan works with the engine running, the switch is bad and needs replacing. Use a lower temp switch which is RED and not the higher temp switch which is Green. This allows the fan to come on sooner. The switch
removal will allow all the freon to escape (unlike newer cars) and will have to be recharged.

If the fan doesn't run look for a bad fuse and check your AC relay
to repair the fan operation.

Good luck with your AC fix.

TobiasMB
3 MBs

PS. The AC freon leakage happens through the porosity of the hose, due ti its construction.

md21722 · #7 05-14-2004, 02:09 PM

Yes, it can be recycled and re-used.

You'll need to find a shop that works with R-12.

The dealer would insist on converting it to R-134a.

Regards,

#8 05-14-2004, 02:22 PM

The system certainly has a low charge. The fans will not come on with a low charge because they are turned on by excessively high, high side pressure. Since you have a low charge, the high side pressure will never reach the limit to turn on the fans.

Don't worry about the fan until you've charged the system.

Good luck,

Jim Anderson · #9 05-14-2004, 02:31 PM

If they empty the system, make sure you get it back. The last time I went to an AC shop I busted them and they put it back, but I noticed they filled my half full system and didn't charge me

My question: is there an acceptable loss rate? Or periodic re-filling? Or maybe a leak that is too small to find and fix?

brookspw · #10 05-14-2004, 03:23 PM

Quote:

Originally posted by LarryBible
The system certainly has a low charge. The fans will not come on with a low charge because they are turned on by excessively high, high side pressure. Since you have a low charge, the high side pressure will never reach the limit to turn on the fans.

Don't worry about the fan until you've charged the system.

Good luck,

The fans DO work.

Larry, assuming the vacuum test proves no leaks, about what would I be paying for the test and refill of r12 and oil?

Thanks

brookspw · #11 05-15-2004, 08:48 AM

bump

#12 05-15-2004, 10:43 AM

Without totally rereading the entire thread, I'm not sure why you are wanting to do a vacuum test. You would have to recover existing charge and then evacuate to do a vacuum test. A vacuum test, as you call it, will only find a large leak. We used to call that a gross leak test.

Since it has a partial charge, why not add UV dye and maybe an ounce of oil and charge the system. Then observe with a black light while it is cooling properly. That way you can get condensation water and shine the black light in that water. If there is dye in it then you know the evap is leaking. If it's leaking elsewhere you can then find that leak.

Once you spot the leak, THEN you can recover the R12, repair the leak, evacuate and charge.

Don't add anything but a small amount of oil to the system unless you flush everything. Otherwise you can easily get it over filled because you don't know how much oil is in the system to start with.

As far as rates for this work in your area, I'm not much help. To fill with UV dye, an ounce of oil and some R12, I would think you would be looking at somewhere between $100 and $200.

Good luck,

Tobias MB · #13 05-15-2004, 11:03 AM

Then, I would still change the high pressure switch to a RED one just for the reason to have the auxiliary fans to come on at a lower pressure which helps with the cooling issue.
You never stated at the beginning of the thread that the aux. fan worked OK but it helps for it come on sooner than originally designed and not an expensive upgrade while 'in' the system.

TobiasMB
3 MBs

brookspw · #14 05-15-2004, 11:18 AM

Quote:

Originally posted by Tobias MB
Then, I would still change the high pressure switch to a RED one just for the reason to have the auxiliary fans to come on at a lower pressure which helps with the cooling issue.
You never stated at the beginning of the thread that the aux. fan worked OK but it helps for it come on sooner than originally designed and not an expensive upgrade while 'in' the system.

TobiasMB
3 MBs

So, when I am getting this A/C fixed, I just ask them to switch this out, too? Sounds like a good idea.

brookspw · #15 05-15-2004, 11:22 AM

Quote:

Originally posted by LarryBible
Without totally rereading the entire thread, I'm not sure why you are wanting to do a vacuum test. You would have to recover existing charge and then evacuate to do a vacuum test. A vacuum test, as you call it, will only find a large leak. We used to call that a gross leak test.

Since it has a partial charge, why not add UV dye and maybe an ounce of oil and charge the system. Then observe with a black light while it is cooling properly. That way you can get condensation water and shine the black light in that water. If there is dye in it then you know the evap is leaking. If it's leaking elsewhere you can then find that leak.

Once you spot the leak, THEN you can recover the R12, repair the leak, evacuate and charge.

Don't add anything but a small amount of oil to the system unless you flush everything. Otherwise you can easily get it over filled because you don't know how much oil is in the system to start with.

As far as rates for this work in your area, I'm not much help. To fill with UV dye, an ounce of oil and some R12, I would think you would be looking at somewhere between $100 and $200.

Good luck,

Thanks, Larry. As I am not an A/C expert, I was thinking that a vacuum test was the preferred/mandated way to testing when in my low freon situation. Thanks for explaining to me.

Just to summarize: 13 year old 190. Never recharged with Freon. Slowly cooling less and less the last 3 years. Does work fine at speed. Just asking for diagnosis/suggestions/cost. Any thoughts are appreciated.