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Conversion of R12 AC system to R134

I am planning on changing out the refrigerant from R12 to R134 on my 1977 Dodge B300 van (360 V8 engine). At the same time I will renew the AC hoses and plan on having a hose company make up new ones while reusing my existing fittings. However, I noticed that the AC hoses have these can shaped “mufflers” installed inline. Are these “mufflers” designed to reduce the pulsations coming from the reciprocating compressor? Since I can’t locate new ones, can I eliminate them without harm to the system? Any help on my questions would be greatly appreciated.

Most of us recommend hiring a certified air conditioning technician for this type of work. Even the best DIYers usually farm out A/C work.

If your AC system is operational then I suggest that you just buy a kit to change from R-12 to R-134. It will be a lot less expensive and will remove a lot of unseen problems in the future. I don’t recommend modifying the system other than changing the refrigerant.

I have done this successfully before on my 1984 S-10 blazer complete with flushing, o-ring renewal and replacement of receiver. However that blazer had a rotary compressor. My 1977 B300 van has a reciprocating compressor. I never saw these can type mufflers (at least that’s what I think they are) on an AC line of a late model car with a rotary compressor. If I can’t find these mufflers I was wondering if I can safely eliminate them.

The system is operational, however the hoses are original and don’t look too good I think failure is evident. That’s why I am planning on replacing the hoses and requesting info on these in line mufflers. Obviously the system was designed with it so I guess the real answer is to find a replacement but not sure where to get them.

Regarding just changing the refrigerant out. The instructions on my last conversion job (on my 1984 S-10 blazer)recommended that I not only flush the whole system but I change out the receiver/drier and O-rings cause the oils used in R-134 are not compatible with R-12.

These are mufflers, and without them a thumping noise in the AC system can develope from the compressor.

Since you’re having new hoses made up, have the mufflers installed to the new hoses. Just flush them clean before they’re installed.


Most of the R-134 cans do not have any oil in them. I think you can buy a compatible oil for 134 conversions.

I did 3 conversions, 2 on Toyotas and 1 on a Ford Crown Vic. Doing my research, the best compressor oil to use in retrofits is the ester POE oil. PAG oil is more sensitive if any of the R-12 oil is still in the compressor or lines, and ester POE oil is more forgiving. Also, ester POE oil only has one weight, PAG has different weights. It is good to do the flushing and replace the receiver/dryer. Also replace the orifice tube. Cheap insurance, since the system is going to be opened up.

Also, I agree with Tester that those are mufflers to quiet the pulses from the compressor. You should be able the keep them when they refit the rubber lines.

Yes they are designed to absorb pulsations from your compressor.

No, if you eliminate them, it will allow your lines to vibrate severely and shorten their life.

If you fix the leaks, your system will run much more reliably with R-12. R-12 is still available. No, you can’t buy it at Wal-Mart, but it is still available and it’s the most reliable refrigerant you can use. I use it in my classic vehicles because it works better and I don’t have to worry about a burnout.

Retrofits are a crap shoot. The question is not if you will run into a burnout, it’s when will you run into a burnout.

609 MVAC tech

I want to thank you all for your comments. You all have given me some good food for thought. I like the fact about keeping my 1977 B300 van’s R-12 AC system as designed and will give it some additonal consideration. I am torn though. I like the fact that I can work the entire R-134 conversion myself including the recharge. Although I can do most of the work on an R-12 repair myself, the price of getting a full R-12 charge is out of sight!

Aside from the bad hoses, the other reason I need to open the AC system is to properly repair the fan/evaporator housing. Apparently, sometime during the van’s 30 year lifetime, the condensate drain got clogged, water pooled in the housing and rusted out a good portion of the bottom and side sending most of the hot/cold air into the engine compartment (not very efficient). Since I am that far in the system, I even considered replacing the evaporator coil while I am at it.

Anyway, based on reading some of the posts below I have two additional questions:

  1. Some of you suggested (when renewing my AC hoses) to flush out and reuse my existing in-line mufflers. If I find that they are full of rust (meaning the baffles inside are gone) would anyone know of a company that sells new ones?

  2. If I went the R-134 conversion route, several of you agreed that a system flush should be performed and the drier/reciever and orifice should be replaced. Would I also need to change out the pressure switch and thermoexpansion valve?

Thanks for your help,

If the system is operational, there should be no rust in the mufflers because there’s no air/moisture in the system., and the refrigerant oil coats the inside of the mufflers.

Anytime a conversion from R12 to R134a is performed, the system must be flushed to remove the minerial oil used in the R12 system.

Replace the reciever/drier because the desiccant material in the R12 component is not compatible with R134a.

The system will have either an orifice tube or an expansion valve. Not both. If it has an orifice tube replace it with a variable orifice tube. If it has an expansion valve it’s a good idea to replace it while the system is apart. Doing either of these will insure you get the best performance from the AC system after the conversion.

No pressure switches need to be replaced.


Aproached another way, have you considered what you would gain buy moving into a vehicle that was R134A equipped when new?

For me a repair/conversion such as this puts the vehicle in the “time to retire” catagory (others may differ, I acknowledge their viewpoint).

My rule with functioning R12 systems is keep it charged until a component failure happens.

What price have you been quoted by a shop to simply bring the charge level up to spec.? Are we really dealing with a system that has a leak greater than allowed when the system was designed?

I do see that you need some evaporator housing repair, another reason to move on to a different vehicle as I believe it would be hard to find a buyer that would part with over $200.00 in cash for your 1977 Dodge van.