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Converting a/c - replace seals or not?

I have heard the new refrigerant eats up old seals and you have to switch them when you switch over.

I have also heard that the old seals can work just fine, so just get fittings and go for it?


As far as I’m concerned the story about eating seals is an old wives tale right along with the one about using barrier hose to prevent refrigerant molecules from leeching through the rubber.

Done a number of conversions without changing a thing and suffering one problem.
Maybe any leak complaints are actually due to aged seals and the refrigerant conversion is getting the blame instead.

Sounds like I want to go for the conversion then (sounds like football). I will look for just fittings somewhere. The old refrigerant has been pulled out and did find a leaking schrader valve that I replaced, but would you recommend leaving it on an a/c machine for a long period of time to vacuum any more out? And then “stress-test” it somehow to see if all leaks cleared? Does it basically apply a pressure and see if the system holds it? Thanks a lot!

Before recharging the system really needs to be put on a vacuum pump for a while.(referred to as an “evacuation”)
The purpose of this is to not only remove the air but more importantly, the removal of moisture.

An electric vacuum pump is expensive. An air operated one is inexpensive but it requires a compressor to operate. Some rental stores have electric vac. pumps for rent but they’re a bit pricy. (About 40+ bucks a day around here I think)

The best way of checking for leaks after recharging is with an electronic sniffer. (also a bit pricy if you buy one)
Another method of determining if you have a leak worth worrying about is by using the vacuum pump to suck the system down. (a 5 minute evacuation will do)
Shut the refrigerant gauge valves off and allow the system to sit for a few hours.
The vacuum reading on the gauges should remain the same after a few hours as it was when this test was started.
If the gauge reading is falling then there’s a leak somewhere.
This is the method I always use on the preliminaries.

At least this method saves the time and refrigerant involved in recharging, discovering a leak, and then going back to square one. Hope that helps.

I ahould have added that you should make sure that you add a few ounces of the correct refrigerant oil applicable to the type of refrig. and make of car.
(PAG, etc. although I generally use Ester oil)

I can use the school equipment - I will see exactly what they have. My seals may be in the aged category - can visually inspect them? Have not used the system much in the whole time I have had the car, but the seals are old. Maybe I should go for the NAPA kit with all the O-rings too. Hmmm. If It eventually does get recharged and the old seals leak - am I in danger of breathing the stuff?


Leaking refrigerant from seals will not harm you at all. Refrigerant can be dangerous if exposed to flames (creates Phosgene gas, like was used in the trenches in WWI) or if a sudden refrigerant release occurs directly in front of you.

A can explosion, hose explosion, etc. will release a cloud of sub-zero gas in steam cloud and this could do some lung/tissue damage if inhaled along with possibly causing frostbitten fingertips in seconds and blindness instantly if the refrig. gets on or in those areas.

Two tips if you do this yourself.
Wear goggles.
NEVER, EVER, open both the low and high side valves on a gauge set while the valve is open on a can of refrigerant. This can cause can explosion. I’ve actually seen this happen a few times and thankfully the guys doing this were uninjured although it certainly created a large steam cloud of excitement.

We put a vacuum on it and it took less than 15 minutes to see both gauges move. I don’t know if the high side gauge losing vacuum means there is a leak in a certain part of the system or if it simply could be anywhere - o-rings or seals. I only replaced an obviously leaking schrader valve. Maybe I should also do the other one in case they have silent leaks and it is easy to change out. Is the next step to get just fittings to recheck it on the new refrigerant machine, or start replacing o-rings and pull out the compressor to clean all the gunk off and look at its seal?

The warning you give above - how do you charge correctly then - an open can to either the high or low side but not both? (Sorry I have not had A/C class.)

Is there an easier/cheap way to find a leak? Must you fill the whole system with new refrigerant to check with UV? You can’t do it with just air and UV dye? The school apparently does not have a sniffer.

Can you put pressure on the system and go around to the joints and put soapy water and see if it bubbles? Or the leaks could be too slow to catch that way?

Is there an “order” of things to suspect like always go for the compressor seal first, etc.?

Thanks a lot.

NEVER EVER EVER Charge on the high side. ALWAYS charge on the low side.

Load up the system with a can of refrigerant with leak detecting dye, and look for the leak. It will cost you a can of refrigerant, but cheaper than a sniffer. Fix the leak once discovered, and retest with vacuum.

BTW, compressor seal leaking means replacing the compressor. Pray for an o-ring leak at a joint.

OK They are 20 year old o-rings so maybe this is their replacement interval anyway. I hope they are fun to change out. So one can with dye is good enough - don’t need to top it off with 3 to fill it up? Thanks.