300SDL A/C troubleshooting/repair? - PeachParts Mercedes-Benz Forum

83w126 · #1 06-05-2019, 03:06 AM

How feasible is it to repair the air conditioner when it's all there as far as I can see, but does not work and probably hasn't in many years? The heater works and the blower will turn on but that's it.

I don't feel like I have the skill to find what wrong or the ability to learn how to figure it out, but it may be easier than I think it is.

I have fixed quite a bit of other stuff and runs and drives pretty well, but after driving it on a hot day the first few times since I bought I have realized that I am too old to drive a car with no A/c anymore, so unless I can fix it I will have to sell the car.

pimpernell · #2 06-05-2019, 07:54 AM

Quote:

Originally Posted by 83w126

How feasible is it to repair the air conditioner when it's all there as far as I can see, but does not work and probably hasn't in many years? The heater works and the blower will turn on but that's it.

I don't feel like I have the skill to find what wrong or the ability to learn how to figure it out, but it may be easier than I think it is.

I have fixed quite a bit of other stuff and runs and drives pretty well, but after driving it on a hot day the first few times since I bought I have realized that I am too old to drive a car with no A/c anymore, so unless I can fix it I will have to sell the car.

There are members on this forum that have the ability to diagnose and fix the a/c system, but it is a whole different animal to start from scratch for the do-it-yourself mechanic. There are some basic test you can perform, but if they do not fix the problem, you have to have the knowledge, gauges, and tools to really delve into the system to find the issues that need to be fixed.

Father Of Giants · #3 06-05-2019, 09:10 AM

Ask Diseasel, he's gone through hell and back with his.

Diseasel300 · #4 06-05-2019, 09:24 AM

Quote:

Originally Posted by Father Of Giants

Ask Diseasel, he's gone through hell and back with his.

And I overhauled the 350SD in exactly the same way and have just as cold A/C.

The key is NOT to skip steps or take shortcuts. Reseal EVERYTHING while you have it apart, replace the filter/drier, the pressure and aux fan switches, Schraeder cores, and the expansion valve while the system is open. While you have it apart, give it a good flush with A/C solvent and blow dry well with compressed air. Use PAO or POE oil and pull a good vacuum. Charge properly, and you'll be rewarded with a 30+ year old car that cools as good or better than a new one (I run 134a too, much to the disdain of many on this forum).

kuene · #5 06-05-2019, 05:13 PM

Last year I overhauled my AC system on an 1982 300D - with no prior AC experience at all. I did pretty much was Diseasel says above. In fact I'm sure he helped me solve a couple problems along the way. Here is how I approached.

1) I wasn't sure of the condition of my compressor as I had no info from PO - though it wasn't seized. I picked up a new (or rather rebuilt) one for around $150 or so - this was the most expensive single item. Everything else is pretty cheap. Getting the old one out and the new one in was the most difficult part of the whole job - heavy, under the car, getting it in while spilling out carefully measure oil, etc. Many folks here implored that I convert to a Sanden compressor while I was doing this job, but I stuck with the original R4 setup. Of course they were probably right, and I will probably do that should this compressor crap out in the future.

2) I replaced the receiver drier, the low pressure switch, and temp switch (both those things are installed on the new drier). I replaced the expansion valve (this was the second most difficult job to do - access was tight in the glove box area). I also replaced the evaporator temp sensor.

3) before hooking up the new compressor or drier, I flushed all the hoses, the evaporator and the condenser with ac flush. Installed new shrader valve cores. I replaced all the orings I touched - which was nearly all of them - I used a little Nylog on all of the orings and cores. I couldn't get to a few orings deep in the engine bay on some of the big hoses.

4) I bought a simple r12 manifold/gauge set. While I have accumulated a supply of r12, I decided to use r134a for the first charge/trial in case I screwed up and had a leak or something. For this reason I chose to use Ester Oil, which is compatible with both r12 and r134a. The oil had UV dye so I could hunt for leaks with a UV light kit.

5) I bought a cheap but effective vacuum pump. Soon after installing the new receiver drier as the final component in the system, I held vacuum on the system for a good while to remove as much moisture as possible (hopefully all). From the vacuum state I then charged with the appropriate amount of r134a for this car (derived from the indicated r12 amount posted on my radiator support).

6) Started the car/AC up. I followed the recommended procedure for breaking in the new compressor and clutch. AC blows fairly cold with r134a. Does the job in Northern NJ summers. I'd imagine I'll get better cooling when/if I decide to switch to my r12.

Coda: I was a bit of an idiot and decided to buy a "heavy duty" version of the compressor, as other people have done. Well, I bought a version of the 4-Seasons Heavy R4 that was clocked incorrectly for this car, which means it's basically mounted upside-down. It works, but about half the AC internet thinks that matters and it will eventually explode for lack of proper lubrication, and the other half thinks it's fine. I also lost most of the oil I had measured and loaded into the compressor when I was installing it because my front end was up on ramps, and the oil just spilled out when I took off the port cover. I made some guess work and tried to put back in the lost oil in from the removed shrader valve in the lowside line near the top of the radiator, upstream from the compressor. So - I really have no idea if I have the correct amount of oil in the system. The compressor is pretty noisy and warm, so I suspect it will crap out sometime soon. Won't make that mistake the next go-round.

This was a time consuming job but not impossible for a completely green and new mechanic such as I am. Before this the only other major jobs I've performed on my 300D was fixing several parts of my vacuum and lock system, and the full R&R of the brake system (minus the booster and the hard lines).

ROLLGUY · #6 06-06-2019, 11:45 AM

Quote:

Originally Posted by kuene

Last year I overhauled my AC system on an 1982 300D - with no prior AC experience at all. I did pretty much was Diseasel says above. In fact I'm sure he helped me solve a couple problems along the way. Here is how I approached.

1) I wasn't sure of the condition of my compressor as I had no info from PO - though it wasn't seized. I picked up a new (or rather rebuilt) one for around $150 or so - this was the most expensive single item. Everything else is pretty cheap. Getting the old one out and the new one in was the most difficult part of the whole job - heavy, under the car, getting it in while spilling out carefully measure oil, etc. Many folks here implored that I convert to a Sanden compressor while I was doing this job, but I stuck with the original R4 setup. Of course they were probably right, and I will probably do that should this compressor crap out in the future.

2) I replaced the receiver drier, the low pressure switch, and temp switch (both those things are installed on the new drier). I replaced the expansion valve (this was the second most difficult job to do - access was tight in the glove box area). I also replaced the evaporator temp sensor.

3) before hooking up the new compressor or drier, I flushed all the hoses, the evaporator and the condenser with ac flush. Installed new shrader valve cores. I replaced all the orings I touched - which was nearly all of them - I used a little Nylog on all of the orings and cores. I couldn't get to a few orings deep in the engine bay on some of the big hoses.

4) I bought a simple r12 manifold/gauge set. While I have accumulated a supply of r12, I decided to use r134a for the first charge/trial in case I screwed up and had a leak or something. For this reason I chose to use Ester Oil, which is compatible with both r12 and r134a. The oil had UV dye so I could hunt for leaks with a UV light kit.

5) I bought a cheap but effective vacuum pump. Soon after installing the new receiver drier as the final component in the system, I held vacuum on the system for a good while to remove as much moisture as possible (hopefully all). From the vacuum state I then charged with the appropriate amount of r134a for this car (derived from the indicated r12 amount posted on my radiator support).

6) Started the car/AC up. I followed the recommended procedure for breaking in the new compressor and clutch. AC blows fairly cold with r134a. Does the job in Northern NJ summers. I'd imagine I'll get better cooling when/if I decide to switch to my r12.

Coda: I was a bit of an idiot and decided to buy a "heavy duty" version of the compressor, as other people have done. Well, I bought a version of the 4-Seasons Heavy R4 that was clocked incorrectly for this car, which means it's basically mounted upside-down. It works, but about half the AC internet thinks that matters and it will eventually explode for lack of proper lubrication, and the other half thinks it's fine. I also lost most of the oil I had measured and loaded into the compressor when I was installing it because my front end was up on ramps, and the oil just spilled out when I took off the port cover. I made some guess work and tried to put back in the lost oil in from the removed shrader valve in the lowside line near the top of the radiator, upstream from the compressor. So - I really have no idea if I have the correct amount of oil in the system. The compressor is pretty noisy and warm, so I suspect it will crap out sometime soon. Won't make that mistake the next go-round.

This was a time consuming job but not impossible for a completely green and new mechanic such as I am. Before this the only other major jobs I've performed on my 300D was fixing several parts of my vacuum and lock system, and the full R&R of the brake system (minus the booster and the hard lines).

For being a first-timer on A/C, I'd say you did a pretty good job. Without an A/C machine, it is hard to get the proper amount of oil in an R4 because of where the ports are on our cars. On a GM application, most are on top. When an R4 goes bad, it usually distributes it's innards throughout the system. One thing to be aware of whenever a compressor goes bad, is that one should completely flush the condenser and evaporator both ways (in my opinion). The only exception is if a parallel flow condenser is used. It is nearly impossible to flush a PF, so they must be replaced with a new one. For flushing the evaporator, an old TXV (with a hole drilled through the valve) and hoses can be used to flush outside the cabin. Or one can install the modified TXV and flush the evaporator and hoses at the same time, and do so in the engine bay where the interior of the car is safe from the oil/solvent mist.

ah-kay · #7 06-06-2019, 11:15 PM

A/C is not as difficult as one thought. You won't get much change for $1500 if you take it to the shop. So it may be wise to invest on some tools if you might do another A/C job again. You need a gauge set and a vacuum pump as a minimum.

This is what I would do.

1) measure the low pressure switch to check for freon. If it is open circuit then may be you just need a recharge.
2) jump the switch and see whether the compressor runs. If it doesn't then you have more issues with the CCU.
3) if compressor runs then check for leak and recharge.
4) converting to r134 is up to you.
5) I would not flush or open up the system unless you know what you are doing.

Good luck.