AC System O-ring sizes

[Keyav8r]

Does anyone have a list of the AC system o-ring sizes specific to our MJs? I've bought 2 sets of the generic o-rings for R134a (one from Advance and one from Rock Auto) but some of the sizes don't look right. I've assembled the system with all new o-rings (including compressor isolation valves) and can't get a good vacuum to hold. Vacuum pump will pull it down to 1250 microns (27-28 Vacuum on gauges) but leaks back down within 2-3 minutes. I pressure tested the evaporator and condenser with 120 PSI air, submerged them and saw no bubbles. Hoses checked out good also.

When I took some of the connections apart I found some o-rings were cut around the outside, indicating they may have been too large for the joint.

How about some feedback, AC gurus?

[HOrnbrod]

I just repaired a couple of slow leaks on mine. One was at the stem of the high side service valve so I replaced the valve, and the other was the o-ring (5/8") on the low side hose at the back of the compressor. I also replaced the low side service valve and the compressor high side hose o-ring (1/2") while I was at it. But I'm still R12, so this probably doesn't help you at all.  :yes:

[Marine1Texas]

Get a O-ring gasket kit, from big box retail auto store they have all the sizes needed MT2601 kit has the 3 sizes need for the MJ and XJ 87 thru end of mj line. the new orings are good on 134a, r12, 1234yf, and r22 systems

[HOrnbrod]

Good info on the MT2601 Santech A/C System O-Ring kit Nori. :cheers:   What lubricant if any should be used on these A/C o-rings when installing?

[Marine1Texas]

Aladdin Magic Lube OR Super Lube is the best thing to use. It fights off the humidity that can eat away at the o'ring. You can use multi purpose clear grease , but I like Super Lube. I get it by a 3 oz bottle

 

Your biggest enemy in any a/c system is humidity, once it comes in contact with any Freon it will eat holes in gaskets and metal. 98% of all leaks I run into at work is do to humidity. So dry those connections off before you put on your o'rings. If I am working in a wet area, I use rubbing alcohol and then a terry cloth to wipe it down. Then I use the grease on Oring the get it on there quickly.

 

Note do not fill a a/c system with pressure air, you will inject lots of humidity in to the system, making it very hard to clean out, also this will cause early death of your drier receiver. If you must check for leak in a a/c system use Carbon dioxide  Co2.

[Keyav8r]

Don - How did you locate your leaks? Before pulling the whole system out I tried a sniffer and dye. The only obvious dye spot was on one tube of the evaporator. Saw a little dye in the bottom of the evaporator housing. The sniffer was inconclusive.

 

Nori - I'll look for that specific o-ring set. My problem is determining which one goes where. Some of them are close in size (o-ring diameter and ring material thickness) and a couple I put in for my bench test came out "shaved". What is the fit criteria? How snug it is on the end of the tube? Should it be equal or smaller than the shoulder on the end of the tube? Also, the directions with the o-rings said to lubricate them and the threads with compressor oil. Some of my hose ends seemed to need thread lube to pull,up tight.

 

I air tested the evaporator, condenser and hoses with air because I don't have a convenient source of CO2. I pulled all of the AC system from the truck and assembled it on a bench for the vacuum test. I have a new dryer receiver that Indidn't use for the bench test. I may have to put in all new or rebuilt components that are available. The problem is that I haven't been able to find an evaporator with provision for the temperature probe. I did find a used evaporator from a '91 XJ at a JY which didn't leak under pressure.

 

I may just put in a pulley to eliminate the compressor and accumulate new components over the winter for a system rebuild next spring/summer.

[HOrnbrod]

Don - How did you locate your leaks? Before pulling the whole system out I tried a sniffer and dye. The only obvious dye spot was on one tube of the evaporator. Saw a little dye in the bottom of the evaporator housing. The sniffer was inconclusive.

 

Quite easily actually. When recharging with RedTek R12a, I accidentally cracked the high side service valve by mistake. I could hear a small leak around the valve stem so I immediately shut the valve. Then ordered two new R12 service valves, high and low, and while replacing I noticed the low side compressor tube o-ring was nicked. So I replaced both the high/low tube o-rings on the compressor. I didn't replace anything else. Charged it up and check it occasionally pressure gauge at the low side and it's still fully charged and working fine.

[Marine1Texas]

The oring should go on the end with a little push or a stretch nothing big at all. if it is too small it will not be easy to get on, if it is to big you can sure tell because it will not hug the end. 

[Keyav8r]

Thanks, Nori. Thought it should fit snug and be the smaller diameter material.