1966 R-12 suction throttling valve leak

[Harry L.]

I found a freon leak on the top of my STValve where pipe goes in. I tried tightening the nut, but that made it worse. Is there a gasket that goes between that top nut and the valve? If that is not the problem, what could make that leak? thanks for any air conditionng expertise, Dutch

[Larry M.]

Re: 1966 R-12 suction throttling valve leak

I found a freon leak on the top of my STValve where pipe goes in. I tried tightening the nut, but that made it worse. Is there a gasket that goes between that top nut and the valve? If that is not the problem, what could make that leak? thanks for any air conditionng expertise, Dutch

Dutch:

I believe this connection uses an o-ring. The backup nut has only a light torque to hold things together, the o-ring makes the seal. These o-rings eventually deteriorate and leak. Complete o-ring kits are available from many souces, but I buy mine from DR REBUILD. NAPA, O'Reilley's, etc should also be able to supply. The biggest issue is knowing what standard size to get. If you tell me the nut size (what size wrench you use), I can probably estimate the o-ring size for you. They only used about four different o-rings on these cars.

Also, try to buy the green (HNBR) o-rings.......especially if you are/plan using 134a refrigerant.

Larry

[Mike G.]

Re: 1966 R-12 suction throttling valve leak

I your STV hasn't been rebuilt, suggest you change out the diaphragm/piston assy. while you have the system empty. Just a matter of separating the housing per the detailed instruction in the '65 shop manual supplement.

[Larry M.]

Re: 1966 R-12 suction throttling valve leak

Dutch:

Based on a 1-1/16 inch wrench size, the correct o-ring should be an AC DELCO/GM #12. The 12 means that the actual o-ring/fitting size is 12/16 inch (3/4 inch). The corresponding AC DELCO part number is #15-3615 and the GM number is #3094216.

I am assuming that the STV inlet takes the standard o-ring. It is possible that there is a special/unique ID/OD just for the STV connection. That is the reason I like to buy everything in a complete o-ring kit.....so you get at least one of all the sizes. However, if you find that it is a special size, I am certain that the supply house you use will have it as well (just bring in the old o-ring for matching). There are not that many different o-rings for these old cars.

Lube the o-ring, fitting, and the threads with a bit of refrigerant oil and install. The listed torque for this threaded nut is only 30 ft/lb.

Mike Geary also has some excellent advice.

Larry

[Harry L.]

Re: 1966 R-12 suction throttling valve leak

Thanks for the information. I did have my STV valve rebuilt 4 years ago. I hope this could be so easy a fix. My receiver-drier is also 4 years old, should that be changed? Dutch

[Larry M.]

Re: 1966 R-12 suction throttling valve leak

Thanks for the information. I did have my STV valve rebuilt 4 years ago. I hope this could be so easy a fix. My receiver-drier is also 4 years old, should that be changed? Dutch

I personally would not change it out at this time, assuming that you seal up the STV opening when the system is depressured......or do the o-ring replacement quickly.

If for some reason you will have the system open for a few hours, then yes, I would also replace the drier. Regardless, make sure to pull a deep vacuum (30 minutes or more) on the system before checking for leaks and recharging with refrigerant.

If I remember correctly, a drier can remove about a 1/2 tablespoon of water before becoming saturated. In general, driers should last for 5-10 years (or more) in service in a sealed system.

Larry