aljolyn

Tried charging the A/C system, '88 N/A, using low pressure port under car by the compressor. It's been converted to 134. Got a zero reading on the guage with the compressor running. Off it read about 45. Also got a milky foam from the fitting when hooking up the hose. Any ideas as to why it wouldn't take the coolant?

Ben951S

Are you sure you're 'feeding it'?

I was having a hell of a time with a can of 'fake' R12, with the pin fully pulled, it wasn't releasing any gas! I actually had to 'pull up' on the pin after unthreading it for it to release gas in the hose.

Not sure what #s you want, but 0 while running is good, meaning any gas/pressure from your 134a can will go in. You do charge while the compressor is on/running! Just go slow as you are basically feeding the compressor directly. Read stories about dumping in liquid coolant can freeze/damage the compressor.

aljolyn

never did it before so I didn't know what to expect. How long does it take to empty the can?

griffiths

Before you charge the system its preferred that the system is empty and in a vacuum 'state'. This means the previous refrigerant that was in it was 'recovered' and then vacuum was pulled on the system to insure there is no air or moisture.

If you are trying to 'top off' a system, meaning there is refrigerant remaining it you want to consider what is in there: meaning type of refrigerant, how much, and whether is there any air or moisture in there as well.


When you do charge the system, there are 2 methods, however to keep things safe for you I'll only address the gas method procedure:

Gas
Charging with refrigerant in a 'gas' state requires the refrigerant can's outlet to be in an upright position. If the compressor is 'off' (clutch not turning and your engine is off to be safe) you could charge through either low side or high side service ports.
If the compressor is 'on' (clutch engaged) you can only charge through the low side service port. Here is where you can get in trouble! If you attempt to charge the system with the engine running through the high side port the pressure created by the compressor running could back flow into your can of refrigerant and cause it to explode: for example the pressure at the high side is 300 psi and the pressure in your can of refrigerant is only 60 psi.
So, when charging by the 'gas' method its always recommended to charge the system through the low side port.

When a system is completely empty and under a 'proper' vacuum you know there is no air or moisture in the system. If there is air in the system you will never get the proper amount of refrigerant into the system and your system pressures will be higher than normal. If there is moisture in the system the moisture can freeze at the outlet of the expansion valve and cause a blockage; poor performance and improper high and low side pressures.

Typically when charging a system that is under a 'proper' vacuum, if you are using small cans of refrigerant.. the first can tends to go in easily, the second or third can is difficult to get in. This is because the cars refrigerant system's pressure is getting higher than the pressure in the can. To overcome this pressure difference you run the engine and have the compressor clutch engage and increase the rpms of the engine; when this happens the compressor's low side pressure drops below the pressure of your can and sucks the refrigerant gas into the system.

Another method you can use is to increase the pressure of your can by warming it with something "safe", something safe is placing the can in a bucket of warm water. The heat of the water is absorbed into the can and increases the pressure in the can, the can's pressure is higher than the vehicles low side pressure and the refrigerant gas from the can moves into the system..... and you only do this with the can in an upright position. If you turn the can upside down the refrigerant coming out will be a liquid. If this liquid gets into the compressor it will damage the compressor reed valves and other components in the compressor; because the compressor is designed to compress 'gas' and not 'liquid'.

When a system is partially charged, you need to have a can that has a higher pressure than the system (hence the heated can by warm water method).

NEVER try to heat the can with anything other than warm water; do not use other heat sources such a flame or heat gun; that is not smart and could have uncomfortable consequences. If you visit an auto repair shop they typically have a large refrigerant can and use an electric heater blanket to warm the can.

The issue the DIY runs into when charging with small cans of refrigerant is the final quantity. Assuming the vehicle needs for example 30 ounces of refrigerant and you have 2 x 16 oz cans or 3 x 12 oz cans, at some point you cannot properly determine how much refrigerant remains to go in. This is where the P&T relationship comes in. At a given ambient outside air temperature the high side pressure in the vehicle's system should be in a given psi range target. Observing this relationship can tell you if you achieved the goal and or whether the system has air in it.

The vehicle's refrigerant system needs refrigerant oil to keep the compressor lubricated. The refrigerant gas running through the system carries or moves the refrigerant oil. No oil or not enough oil will cause the compressor to lock up, seize, grenade, etc. and create quite a mess in the system which will require many hours to repair. Some small cans of refrigerant come with oil inside. Be aware of the type of oil; if you are using R134a refrigerant this oil can be either "Ester" or "PAG". Its preferred that you remain with the same type of oil that was in a R134a converted system before and ditto for systems that were originally R134a (this came about around 1993).

You NEVER want to put in any 'additives' such as sealants, enhancers or snake-oil. Sealants will, sooner or later, block off pressure switches and in excess can block up expansion valves, driers and even compressors.
Last year we have a client bring in a car with an entirely "new" system installed by a shop. The shop injected a sealant in the system, no one knows why, and it caused the low-high pressure switch to fail 3 times! In other words the vehicle owner had to make 3 appointments to visit his repair shop and they replaced the pressure switch 3 times. The 4th time he visited us to have the system completely removed, liquid flushed with an ac flush agent, replaced the previously new compressor with another and finally the issue was resolved. That required a full 8 hours of labor plus materials. A very expensive mistake by the previous repair shop.

If you are 'topping' off a system then chances are the system has a leak.
So, find the leak(s) and fix it.

aljolyn

found out why it was 0 pressure. Screwed the valve on the can to puncture it but didn't unscrew it to let gas thru.

griffiths

Who reads the instructions anyway

phlfly

I'm looking a low pressure port for 1989 944. I read and it looks like located right near compressor or thick pipe, that started as rubber hose than becoming aluminum pipe.
I had tried connected adapter and oil started leaking out?(gravity?) So it either adapter is crap or I do something wrong. I did before on other car with R12 and all fitted right.

Thanks for help

snb13

A year later I find this thread because I did the same thing. DOH!

griffiths

The ac oil is spread out through out the system (compressor, drier, evaporator, condenser and hoses; each holding a given amount based upon its surface area and whether gravity will allow it to drain).

If you are attaching an R134a service adapter that has its own schrader valve inside, you would remove the existing schrader valve from the R12 service port before you screw on the R134a adapter.

Its common for refrigerant oil to drip out, all based upon gravity as mentioned.