R12 to R134A conversion problems

[Mattheww044]

Hey guys, I tried doing the conversion from R12 to R134A today. This is the first time I have ever tried doing this but it seems pretty straight forward so I go for it. Once all of the R12 was released, we hooked up the new can with the gauge on the adapters. I started the car and put the max A/C on 4. We hooked it to the lower stem and the gauge immediately went into the red "range", which says something is mechanically wrong with the car. Does anyone know what this could be? I have never worked on the A/C system of a car. but its time to start! haha thanks ahead of time.
Matt

[93forestpearl]

While you are adding refrigerant, you'll be reading the pressure that is in the can, not in the low-side of the AC system. Turn the needle back into the can to seal it off and you should get system pressure.

[Mattheww044]

hmmmmm..... well my buddy Jordan was doing it, and he just did it to his car (an ss as well) yesterday. On the gauge it went into the red zone, and on the back it says if it goes into the red zone do not add refridgerant, there may be a mechanical issue with your A/C system

[93forestpearl]

Check the system with the gauge without a can attached to it to make sure you get the proper low-side reading.

When I was filling, the gauge was up in the 90 psi region until I closed the valve so only the system pressure was working on the gauge.

[Mattheww044]

O I see what your saying. How long did u have to sit there and shake the cam forit to start working?

[SubyFusion]

It takes about 7-10 min per a can, my hand hurt after a while lol but ya what he said is correct it is reading the pressure from the can. Just fill it with 28-32ounces and you should be more then good. Also did you vacuum the system or change the oil? these need to be done before adding r-134a.

[Legacy777]

Are you guys changing oil or putting a vacuum on the system? If not, don't expect things to work well if at all.

The mineral oil in R12 systems is not compatible with R134a refrigerant. Additionally, the receiver drier needs to be replaced and a vacuum needs to be pulled on the system before you charge it with R134a.

[Mattheww044]

ahhhh found the problem, the compressor will turn on, but not stay on. SO something was mechanically wrong. I will replace that and start from there.

[subytech]

Are you guys changing oil or putting a vacuum on the system? If not, don't expect things to work well if at all.

The mineral oil in R12 systems is not compatible with R134a refrigerant. Additionally, the receiver drier needs to be replaced and a vacuum needs to be pulled on the system before you charge it with R134a.

Bump

Also R-134a is made up of much smaller particals (sp?) and will leak out over time if you dont replace all the o-rings and soft lines in the system with r-134a compatable parts. Napa sells conversion kits with the most of the required parts. And you cant use the same amount of 134a as r12 because of their different expansion rates, cant remember what the conversion rate is off the top of my head, but to do it right you should keep these things in mind.

[subytech]

ahhhh found the problem, the compressor will turn on, but not stay on. SO something was mechanically wrong. I will replace that and start from there.

I bet your compressior is fine and your pressure switch is preventing it from coming on because of the lack of pressure in the system. You need to get at least 1/3ish amount of refridgerant in the system before the compressor will stay on. Also they do cycle, its normal for the compressor to turn off every 15 sec or so.