who's the a/c guru here?

[poppa]

94 gmc Yukon .350ci .no cool air. Static press 5 (both sides) .truck running .jumping switch at firewall .clutch engaged .30 psi low side .35 psi high side. I was going to try to add some r134 unless someone has a better way for me to start?

[Pete in NH]

Hi,

I would say with a static pressure of 5 pounds, the system is virtually empty. Be careful about running the compressor with so little refrigerant in it. The compressor depends on the refrigerant carrying oil around the system to lubricate it. The compressor is not running unless you jump the switch because the system is empty.

You will need to find the leak, repair it, and vacuum down the system, then recharge it into the vacuum.

[John_Kunkel]

It's perfectly normal for a system to leak off refrigerant over the years, some residual pressure in the system precludes any air/moisture entry so just jumper the switch and add refrigerant through the low side fitting.

https://www.youtube.com/watch?v=w8Mw_dGFLjo

[Nwcharger]

I would say charge it up and watch your pressures. Depending on outside temp the high side should be around 150-200 psi and low side should be around 30-40psi. If your charged up and your high side pressure is still low I'd say the compressor is no good. if you have a blockage the low side will pull to 0 and your high side will spike.

[69wannabe]

Just got my jeep going last november that I bought with a bad engine earlier in the year. I knew when I got it going that the air didn't work but it was winter time so I didn't mind running without it through the winter. Put my gauges on it and it pretty much had none in it. Pulled a vacuum on it for about an hour and then let it sit for another hour and it held a good vacuum so I put 2 cans in it and it worked great for about a month. Noticed yesterday that itg was not blowing as cool as it was so I put the gauges back on it and it was low so I put another can in and it is back to good now. If it last's a month at a time then I will just add a can til summer is gone since it such a slow leak there is no telling where it is leaking at. I do have a blacklight so if it get's really bad I will try to see where it's going...
it's always good to pull a vacuum on it tho just to get a good reading on the system!!

[Pete in NH]

It is normal for a system to loose its charge over a period of many years. If your system is all original and has not had refrigerant added in many years you certainly can try adding more R-134A. A 1994 should be in the early years of R-134A. Although, you may find your new refrigerant doesn't say in the system.

Rather than jumping the pressure switch when adding R-134A, I would hook up  can of R-134A, purge the hoses and connect to the low side service port. With the ignition switch on, but the engine not running, turn on the A/C system. When the new R-134A pressurizes the system to a safe point the A/C compressor clutch will click in. Now start the engine and pull in the rest of the refrigerant. This way you don't risk the compressor not getting lubrication.

I would add R-134A with a bit of U/V dye. That way if you have a leak the U/V dye and a black light will help find the leak. Don't add any type of sealer with the R-134A. Some sealers are relatively harmless seal and O ring swelling compounds others are silicate types that can really mess up your A/C system if things go wrong.

[poppa]

Thanks for all the replies and advice/suggestions. After work tonight I hooked up the cheapie vacuum 'pump' I have had for years (it seems to work !) , got it to vacuum (30) . It does not seem to want to take the Freon. My guess is blockage. If correct what's the easiest way to find out what's blocked?? I already have a new orifice tube and accumulator that will automatically go in but want to make sure the block is gone too.

[Pete in NH]

The most common cause of not being able to get the refrigerant in he system is the coupler on the gauge set not depressing the valve on the inlet service fitting and it happens more often than you would think.

Are  you using a real R-134A gauge set or one of those Walmart single hose with a gauge things?

You want to charge the R-134A into the low side service fitting as a gas. This is fairly easy to do but, some people get confused if using a real gauge set as to which hoses go where and what side valves to open and close. Let me know if you need help with that.

[poppa]

I have a manifold set I bought along time ago from Harbor Freight. The coupling seemed to work with the vacuum part , I think I have just a hose set up. I will try it next chance I get. Should I redo the vacuum part since I tried to fill it?

[Pete in NH]

I would use the full gauge set, those single hose things usually have really poor couplers on them. One the full gauge set, blue hose to the low pressure service port and left side gauge. Yellow hose to gauge set center port. Red hose to high pressure  service port and right side gauge on the gauge set.

I would re-vacuum the system as you don't know what might have allowed air in. The Yellow hose goes to the vacuum pump. With both side wheel valves on the gauge set closed start the pump. Them slowly open both side wheel valves. If you are really connected to the A/C system, the left gauge will slowly start to show vacuum. If the left gauge quickly goes to -30 vacuum it is likely the coupler are not opening the service port valves.

I let the pump run at least an hour, you want to pull out are much moisture as possible. Then close both side wheel valves on the gauge set. Disconnect the vacuum pump and let the system sit for a few hours. You should not see any change in vacuum reading on the left gauge. If you do you have a leak somewhere.

If all is well, tap the new can of R-134A and connect it to the yellow hose. Open the can tap valve the then purge the hose by loosening the yellow hose coupler at the gauge set and allowing some R-134A through. Retighten the hose coupling  and open the left side wheel valve on the gauge set. leave the right side wheel valve closed from now on. The vacuum should now draw the R-134A into the system and both gauges should go from showing vacuum to pressure.

[poppa]

If the left gauge quickly goes to -30 vacuum it is likely the coupler are not opening the service port valves.

What's quickly??

[Pete in NH]

If the left gauge quickly goes to -30 vacuum it is likely the coupler are not opening the service port valves.

What's quickly??

2or 3 seconds.

[poppa]

Thanks Pete. If I'm lucky ,and the planets align properly ,I'll get to try on Sunday. Thank you

[poppa]

The most common cause of not being able to get the refrigerant in he system is the coupler on the gauge set not depressing the valve on the inlet service fitting and it happens more often than you would think.

Pete , I think I have a problem with this. I bought a can with a hose attached ,thing leaked like a sieve ,but .... I could tell it was going in ,the tube actually got cold , too. Probably half the can leaked out (hose and coupler were plastic. How do I know how far the 'injector' in the coupler should be from being flush with the end??? Also , problem #2 , when I disconnected the plastic coupler , the low side valve/coupler on the car ,leaked. Can that work again (close) with just a shot of wd40 or something??? Thanks

[Pete in NH]

Those cans with a hose and plastic coupler attached are nothing but trouble as you have seen. Good A/C service work isn't hard to do but you really need the right tools. Those "magic Wal-Mart cans" can often get people in trouble thinking they can short cut good service procedures. Those cans often contain sealers promising to fix leaks and save you big money over taking the car to an A/C shop. Some of the sealers used can totally screw up a system if things go wrong. Many A/C shops will not touch a system with a sealer in it for fear of ruining their recovery equipment. The best advice I can give you is stay away from those types of cans and use only regular R-134A cans, a can tap and your regular gauge set as the charging hose. The R-134A cans should be plain R-134A, maybe some U/V dye but NO sealers.

As to the leaking low side service port, it depends on the leak rate. If it is leaking really badly you will have to likely replace it. I don't know about your 20+ year-old GM system but the valve cores can often be replaced or tightened with a valve core tool. All my experience is on Chrysler systems. I do know that GM often has the low side service port on the accumulator ( silver can) which can be replaced as an assembly.

If the leak is very slight, the plastic cap that covers the service port should have an O ring in it. That cap and O ring are meant to be a secondary seal on the valve. If the O ring in the cap is in good shape, a drop of refrigerant oil on it and you should be all set. If the o ring is all hard and dried out , replace it. Those plastic caps and O rings should always be in place on service ports to keep dirt out and the R-134A in.

[poppa]

Well....I have air. For now. Got the valve to stop leaking before adding Freon. When I got done and removed the gauges it started leaking again. I'll see how it goes for a couple days. I mostly wanted to know if it was going to work or not and still have a new orifice and accumulator. The Freon I bought was pretty cheap (on sale) and I still have some of the "better" stuff. It's pretty cool here today but Friday it's suppose to hit 90. Thanks to everyone for your input and time. If anything worth posting comes later , I will.

Pete , that coupler was not depressing the valve. Got another one and presto. Thanks

[b5blue]

You can "rent" tools from Advance Auto. You buy/use/return for a full refund. I called and talked to them about it. To charge my new A/C in my 70 with R134 I bought a 14.00 digital scale off Amazon to gauge amount of Freon added. I'll rent the vac. pump and gauge set, I bought 3 cans of R134 for about 18.00 off eBay saving just about what the scale cost. Next I'll tackle my 89 XJ's A/c.