Air conditioning refill


I have a 1996 pontiac grand prix. The air condiotining isn’t working. When it’s truned on I can see that the compressor isn’t engaged. I’ve tried to add freon with a can of r134 but it’s not taking any of the freon into the system. I’m using one of those snap on hoses you get at an auto parts store. The gage on the hose shows that there is no pressure in the system. Can someone tell me why it won’t take any of the freon into the system?



I may be in the minority, but I do not include automotive AC systems in the do-it-yourself category. Even if you get some refrigerant into the system you have not repaired the leak from which the original escaped, and you will soon have non-functional AC again.

I take all AC problems to an AC specialist. They have the PROPER equipment to diagnose and repair automotive AC systems. You and I do not.


Agreed that you should not mess with A/C as it can be hazardous to your health.

However, if the system is empty the compressor will not engage because the pressure switch is not able to close the circuit. The switch is usually located near the accumulator and should be jumped with a paper clip or something until the first can is in.

Now. This is an exercise in futility. If the system is empty then you have a serious leak; probably the compressor shaft seal. Attempt to charge it if you must, but don’t expect it to last more than a day.


I totally agree. A/C repair is not for the inexperienced.


I suggest you leave that work to the pro. The fact is, A/C does not consume refrigerant. If you run out it means there is a leak. If you don’t fix the leak it will just leak out again. If you do it wrong, you can damage the system and injure yourself.


The other posters are correct, you are wasting your time…The reason the freon stays in the can is that you don’t know what you are doing. That’s to keep you from hurting yourself.

The REASON has nothing to do with the compressor. It’s because your fill adapter does not open the schrader valve on the fill port or you are not opening the can of freon, it’s still sealed…


Before doing anything else, start with both gauge valves closed. Check to make sure the core depressor is adjusted correctly. If it’s not adjusted correctly, the valve core will not open and the gauge will stay at 0.

If the pressure really is 0, there’s a big leak somewhere, probably a burst pipe or very loose flare connection. Add a tiny amount of refrigerant and try to find where it’s leaking out. You’ll need special tools to repair a burst pipe, but try tightening a loose flare connection. Note that if the pressure dropped to 0, there might be air in the system so you’ll have to change the oil (polyol esters used with R134a absorb moisture very well), replace the filter drier, and pull a deep vacuum. Best to have a good HVAC company do the work if you don’t know how.


I agree with the others – sort of:

  1. The reason that the pressure gauge is showing 0 is because the gases the hose it is hooked to are at atmospheric pressure. That could be because you have valves shut that should be open or because you haven’t punctured the can. It may say that your A/C system has leaks and has dumped its load of R134a. If you don’t hear a hiss at least intially as the can vents into the A/C system, I’d bet on a valve being closed or the can not being punctured.

  2. You surely have at least a small leak. The best case scenario is that the leak is small enough that a can or two of R134a will get you through the Summer. The leak will surely get worse next year, and even worse the year after. i.e. you won’t be fixing the problem – just deferring it.

  3. You can buy a can of stuff at that parts store that advertises itself as leak detector, lubricant, and sealer. So far as I know there is no recorded case of the sealer actually sealing up a system that is leaking, but you could be the first.

  4. R134a is not toxic and it will not eat the Ozone layer. But it is a fairly potent greenhouse gas. About 1600 times as greenhousish as CO2. So try not to vent too many cans of the stuff into the atmosphere while dinking around with your A/C.

  5. What should, I believe, happen, when you do things right is that you should hear a loud hiss and the can should cool down as gas vents from the R134a can into to A/C system. The can should get colder as the pressure in the can drops and R134a expands into the tubes (Boyles Law, Charles Law, something like that). If the engine is running and the A/C is on, the compressor should kick in when the pressure of R134a in the system reaches a level where there is some point in trying to compress it.

  6. If you really need air conditioning, you might as well schedule a session with the local A/C system repair guys now. You can always cancel it if you somehow get the system working. They are usually really busy this time of the year.


After reading the various answers, it is amusing to see that the people who don’t know how to service an air conditioner recommend taking it to a shop. I have added freon 12 to older systems with no problem; have not yet done a 134A system but you can bet that I’ll try before spending hundreds of dollars at a shop as a last resort if I don’t choose to leave the system inoperative.


Adding coolant is easy. Adding coolant to a leaky system is a waste of time and money. There’s a little more to “servicing an air conditioner” than adding coolant, most DIY’s do not have the equipment or expertise to do it correctly.


They recommend taking it to a shop because the simple fact of the matter is that A/C servicing can be dangerous, even for an experienced tech. In the hands of a novice anything can happen.

You’ve probably never had the opportunity to see a can of refrigerant explode. I have; and it happened to a very experienced A/C tech (30 years) in our shop. His mind wandered for a few seconds and he inadvertently opened the high side valve on the manifold gauges while the can was tapped.
A loud shotgun BOOM and both tech and car front end disappeared in a cloud of steam. Lucky for him he was wearing glasses and he was also lucky enough the frostbitten fingers managed to thaw out.

There’s always the chance that even if a can does not pop that a hose (either car or gauge set) may burst, and one tiny drop of refrigerant hitting an eyeball means that future A/C service will be done with one eye only.


It’s the OP who has demonstrated his ignorance and lack of proper tools to service automotive A/C systems, not the people who were offering advise…


If you examine a new can of refrigerant, you’ll notice that next to the valve is a pressure relief device. It is designed to split before the can itself splits. There also is a shield right above the relief device to direct refrigerant away from the valve handle. There should also be a check valve to prevent backflow.

And you’ll have to really mess up to burst a hose. The main problem is using hoses that have worn out or damaged from frequent use. And always watch the high side gauge when charging.


You know; I have been installing and repairing A/Cs for about 30 years and I have absolutely no idea what in the hell you’re talking about - again.

You’re very sadly mistaken if you think a hose or a can of refrigerant cannot burst at any time.

You need to provide a link to that Brothers Grimm A/C repair manual that you use.


I wear a motorcycle helmet with a face shield when adding freon. It may look silly but that’s OK.


I fix my a/c system in my car. It is pretty tough but it is doable. If you have a leak just find it by preshurizing the system with air. DO NOT TURN YOUR A/C ON. If you do you will end up with an overheated compresser which will cost you at least $200 for a new one.

After you have air in the system listen to it and find out where it is. Use water with some sop to find out where the air is escaping from. After you find the leak just replace the part if it is aluminum. Or go to some pros that can weld aluminum and have them weld the hole. If it is copper then it can be soldered like copper pipes. Let me tell you this is not easy. You got to be pretty crafty

But then again you could have a pro look at it and charge you couple hundred dollars to fix it. If you where asked where the compressor is and you do not know then leave it to the pros.


Star is at it again. I managed to get some of his posts removed from the old board and if he insists on giving advice that is nonsense I will atempt to get his posts removed again.


I’m just pointing out that A/C service is safer than it was in the past. Of course, it’s still very far from foolproof and safety precautions are still essential. If you actually go to a HVAC supply store, you’ll find that the old gauges and hoses are rated to 500PSI maximum working pressure, but the new ones are rated to 800PSI. That’s mainly done as R410a systems operate at higher pressures. However, using 800PSI hoses with older refrigerants cannot hurt. About the only ways to burst a hose are to accidentally power up the compressor with the discharge line service valve completely front seated (which is more or less only on refrigeration systems) or using a hose that has worn out or has been damaged. Extremely high pressure can also occur as the result of air in the system or serious overcharge, but the high side gauge should warn of that danger.

That said, screw up badly enough and you’ll have a bomb.
Note that he did not have a way to check the high side pressure and there was no vacuum pump used.

And refrigerant cans can explode, but due to the use of pressure relief devices, it’s much less likely. Of course, refrigerant cans should still be handled carefully as the pressure relief device will not protect against physical damage.


STAR… the systems we are talking about are automotive A/C systems and they don’t use 410. What you have to offer doesn’t apply.


A/C service is not safer. The same procedures are in place now; the only difference is the refrigerant.

You just flat do not comprehend, or flat don’t care, that your recommendations may lead to someone being seriousy injured at the worst or major embarassment at the least when a consumer approaches an A/C shop and asks them to perform a non-existent service or replace a non-existent part.

Your last post is a perfect example. R410a is an alleged “substitute” for home central and heat pump units. You’re telling someone to use R410a in an automobile system? Are you aware that 410 causes dramatically higher high side pressure; as in 50-60% higher? What do you think is going to happen in a car if this is used and a normal 250 PSI reading now decides to hit 375-400 PSI? Bang is what will happen.

Also, where did I say that the gauge set hoses would be the only thing that could burst? Not only is that possible, but the OP has a 12 year old vehicle with equally aged hoses and seals. Any of them could burst at any time during the recharging process.

The OP also states they’re going to use one of those cheap charging hose setups. That may work and not be dangerous, or it may not. A relative had purchased one of those and wanted to add some refrigerant to their system. I volunteered and immediately after tapping the can and opening it, refrigerant started blowing out the PLASTIC can fitting, all due to a crack in the plastic. This led to closing the can (still leaking), wrapping duct tape all around it, and managing to keep everything in one piece until at least half the can was in. Safe? I don’t think so.

As to this alleged pressure relief valve, maybe you can point it out on these cans of 134.