AC system diagnostics

[mikeym]

Both the w124 and f-150 have weak or non -functional AC systems and finally it’s time to fix them properly.

Luckily I got enough r134a cans to refill and don’t have to travel out of state to get them.

Besides the manifold gauge set, connectors, uv dye/flashlight etc, do I need any special equipment?

Any links or recommendations for brands/products?
Everything on Amazon seems to be Chinesium and I don’t trust the reviews.

Thx

 

[gsxr]

You'll also need a vacuum pump, to remove all moisture prior to refilling. Cans aren't the best to fill with, but cost a lot less than a tank and scale.

For occasional use even a Chinesium vac pump should be cromulent. Good ones are a few hundred bucks. With a coupon you can probably get the HF unit under $100 out the door. There are some off brands as low as $70 on Amazon.

https://www.harborfreight.com/25-cfm-vacuum-pump-61245.html

 

[mikeym]

You'll also need a vacuum pump, to remove all moisture prior to refilling. Cans aren't the best to fill with, but cost a lot less than a tank and scale.

For occasional use even a Chinesium vac pump should be cromulent. Good ones are a few hundred bucks. With a coupon you can probably get the HF unit under $100 out the door. There are some off brands as low as $70 on Amazon.

https://www.harborfreight.com/25-cfm-vacuum-pump-61245.html

Thx! I forgot about the vacuum pump.

 

[alabbasi]

Harbor freight will have everything you need including the O-rings. The gauge set adapters tend to leak slightly so I use o rings and teflon tape to keep them tight. If you're not familiar with a/c systems, I recommend getting the Haynes automotive air conditioning manual which I found quite useful when I started trouble shooting a/c systems.

 

[195910]

For optimal performance its best to use an AC service machine. You need exact measurements for r134a, compressor oil as well as a clean leak-free system, filled under vacuum.

The W124 V8 has one of the best A/C out there *if functioning properly*.

 

[gsxr]

For optimal performance its best to use an AC service machine. You need exact measurements for r134a, compressor oil as well as a clean leak-free system, filled under vacuum.

Yes - it's the "exact measurement" part that is difficult with cans. Filling under vacuum is critical to ensure there is no air in the system, which can adversely affect performance. Measuring the oil charge is basically impossible without fully solvent-flushing the system, which is a nightmare. If adding oil, the double-end-capped Denso ND-OIL 8 is highly recommended, details in post #'s 17-21 here.

The W124 V8 has one of the best A/C out there *if functioning properly*.

Agree 100%! I don't know why exactly the late 6-cyl 124's (with factory R-134a) don't seem to cool quite as well, they have the same sized condenser, evaporator, and compressor. The early 124 with R-12 has excellent air conditioning, but it's difficult/expensive to locate R-12 these days, and sadly many of those systems have been downgraded to 134 by now. Converting from R-134a to R-12 is possible but very difficult/expensive to do properly.


:

 

[emerydc8]

The early 124 with R-12 has excellent air conditioning, but it's difficult/expensive to locate R-12 these days

In a few years we’ll be saying that about R134a too. These loons will convince everyone that it is burning a hole in the ozone and the sky will fall.

 

[TerryA]

Since I’ve used the 134a cans in my system I have found that AC Techs don’t want to evacuate the system anymore due to contamination of their equipment.

Has anyone else had this issue or is there a work around?

 

[gsxr]

Shops may worry about contamination when sealants have been used, but a system converted properly from R-12 to R-134a shouldn't be an issue.

Should be zero concerns with factory R-134a systems.

I'd ask for specifics if anyone tells you "contamination of their equipment" in the future.

 

[alabbasi]

If you wish to charge by weight , a postage scale or bathroom scale will do the job. We're car guys so we're going to own a lot of cars. Forget the cans and get a 30lbs jug. You can usually get them for $250-$300 on marketplace

 

[gsxr]

+1 on the 30-lb cylinder! Even better if it's USA-made like Chemours/DuPont but that will cost a little more.

Most bathroom scales won't be accurate enough, they tend to only have 0.5-lb increments. Even a 0.2-lb increment is kinda rough. Really need something with a range up to at least 40 lbs, and 0.1-lb resolution or better. I have this one (but paid ~$175). There are a bunch of budget scales on Amazon around $70-$90:

https://www.amazon.com/s?k=refrigerant+scale

 

[mikeym]

Thx to the king of our state and his loons, can’t get refrigerant shipped here. So, for now, cans is the only option but will keep an eye open if I drive to one of the neighborly states.

Back to the problem the hand, picking up stuff this weekend and will start diagnosing.

 

[gsxr]

Can you purchase a 30-lb tank at the local McParts / FLAPS? You may need an EPA 609 certification, but last I checked you can get this online in less than an hour.

 

[alabbasi]

Most bathroom scales won't be accurate enough, ]

My bathroom scale reads to the the 10th of a lbs, but always 20lbs over what it should :-D

 

[Alphasud40]

Just replaced the compressor on my E420. Did a long evac. and recharged with the 12oz. cans. System capacity is 2.2 pounds which works out to 35.2 OZ or 3 cans. It can be done without a scale. The W124 is a TXV system meaning it has an expansion valve and a sight glass on the dryer behind the drivers headlight. On a hot day with a full charge you will have a clear sight glass. You can also partial charge by using the sight glass and stopping as soon as the sight glass stops flashing and goes solid. Cars with an orifice tube have to be evacuated and recharged unless you are well versed in refrigeration and use the superheat method.

 

[mikeym]

Just replaced the compressor on my E420. Did a long evac. and recharged with the 12oz. cans. System capacity is 2.2 pounds which works out to 35.2 OZ or 3 cans. It can be done without a scale. The W124 is a TXV system meaning it has an expansion valve and a sight glass on the dryer behind the drivers headlight. On a hot day with a full charge you will have a clear sight glass. You can also partial charge by using the sight glass and stopping as soon as the sight glass stops flashing and goes solid. Cars with an orifice tube have to be evacuated and recharged unless you are well versed in refrigeration and use the superheat method.

Thx for sharing.

What did you use to evac?

 

[Alphasud40]

I have a Robinaire 5 cfm vacuum pump. Common leak areas I have seen have been the compressor manifold connection, the condenser, and along the low side where moisture condenses and causes corrosion at the fitting where the o-ring seals. You can purchase an application specific o-ring kit for $20. Replace as many as you can get to and replace the dryer if the system doesn’t have any charge. I was told when R134a became a thing that the desiccant cannot be dried out like the old R12 systems.

 

[gsxr]

Alphasud, what is your preferred method for identifying leaks? Dye, soap/bubble solution, or a sniffer tool?

OEM driers are NLA and there are few if any aftermarket driers that fit the V8 models (without modification anyway). There's a thread from a few years ago with more details. I'd probably use the existing drier (with an extended vacuum period) if there's no concern about debris in the system, excess moisture, other contamination, or other reason to believe the desiccant is non-functional or compromised.

 

[Alphasud40]

I use all 3 methods for leak detection. A dye only works if the leak is low enough in the system for the oil to escape. Sometimes the leaks are obvious. Soap and bubbles work well for condensers when the leek can’t be seen with dye. Also the dye is helpful for evaporators and a good tip is to catch the condensate from the A/C and shine the UV light on it.

A good leak detector can hone in on a leak but it’s more difficult to sometimes find using that method. Again with evaporators leaving the car off and placing the blower fan on low. Sticking the sniffer wand in the vent as you turn the key to the run position can sometimes find refrigerant flooded in the evaporator case or sniffing the evaporator drain if you can get to it also helps.

Yes I have reused dryers in the past especially if the replacement ones are crap. As for contamination if you had a compressor fail the car always gets a new condenser, dryer, and expansion valve. You can’t successfully flush a condenser. Especially newer one that have internal fins inside and the tubes and are parallel flow. With the W124 they still use series flow so they can be cleaned since new ones are NLA.

 

[gsxr]

Great info - thanks for sharing! Just curious, where do you usually see leaks at condensers?

I wonder if a custom parallel-flow condenser would improve performance on 124 systems at idle / low speed. They're not a very common failure, but are NLA.

 

[Alphasud40]

The condensers usually leak from stone impacts but the one on my V126 cracked on the passenger side. That got replaced with a aftermarket parallel flow unit that fit like garbage but I saved that car from the wrecking yard so I was okay with inexpensive. That car worked really well after the replacement since it was originally a R12 system. So the answer is yes finding a parallel flow condenser improves A/C performance and lowers head pressures taking some strain off the compressor.

 

[gerryvz]

The condensers usually leak from stone impacts but the one on my V126 cracked on the passenger side. That got replaced with a aftermarket parallel flow unit that fit like garbage but I saved that car from the wrecking yard so I was okay with inexpensive. That car worked really well after the replacement since it was originally a R12 system. So the answer is yes finding a parallel flow condenser improves A/C performance and lowers head pressures taking some strain off the compressor.

Klima Design Works is producing proper 126 condensers of good quality, FYI. I'd consider speaking with Matthew there if a condenser is needed.