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Wow talk about bringing posts up from the dead!! 😋
I've always worked on my own AC systems the only thing I have to pay to get done is to remove the refrigerant from a charged system. Other than that I have the vacuum pump, system flush tool, gauge set and the other little items that are used. There's a lot of information that is right but some is wrong.
If the compressor is cycling usually that means you are low on refrigerant.
Air in the gauge lines and filler lines can and will cause you problems. Purge the lines before connecting to your system. If you can't legally purge the lines then use your vacuum pump to remove the air.
If your system has been opened for any reason and air has been introduced into the system or the system is completely empty with no pressure you really should replace the dryer. It's the silver tank looking thing connected to the low pressure side of the system. The desiccant inside can only absorb so much moisture before it gets saturated. And moisture is an AC systems worst enemy. Some say the vacuum will remove the moisture from the desiccant but if I had just spent my hard earned cash getting the AC repaired and just vacuumed the system it would be like throwing the money in the garbage cause soon you will be doing even more costly repairs. So just put in a new dryer anytime the system has been exposed to air or has been completely emptied.
Replace the orifice tube. It has a filter on it that gets plugged and then the air won't feel like it's as cold as it should be.
You need to completely flush the old oil from a R12 system before you can retrofit it. The oil from an R12 system isn't compatible with R134a and if it isn't flushed out completely your money spent on the retrofit won't be all your going to spend on the system. No TrailVoy will have R12 though so don't worry about oil.
Having an AC that doesn't work in the middle of summer sucks!! Not being able to afford to fix it really sucks but most AC issues can be fixed with just intermediate mechanical knowledge.
No matter what you do if the system is empty don't just charge it and go. Always vacuum the system at minimum before recharging it. Gauges and vacuum pumps are able to be rented nowadays at the auto parts store and usually it doesn't cost anything just a deposit that you get back after you return the tools. Another reason to vacuum the system is to leak check it. Once you have ran the vacuum on the system for about 20 minutes shut down the pump and mark the gauge where the needle settles. Wait 10 minutes and check it if there is no change wait 10 more minutes and if it is still holding there are no leaks. If the vacuum doesn't hold you have a leak and it needs to be found before you can recharge the system.
Don't use a compressor to pressurize the system. You will need to pressurize the system with nitrogen and dye. The dye coats the area where the leak is and with UV protective glasses and a UV light you scan all the connections, compressor, condenser and any other areas you can access. If the leak is in the evaporator the dye probably can't be seen unless you access the evaporator through the inside. Sometimes the dye will be coming out of the evaporator drain then you know that your going to need an evaporator. There are also refrigerant sniffers that you can use to check the evaporator without having to disassemble the dash.
Just make sure NOT to vent any refrigerant into the atmosphere. Its unlawful and it destroys the environment have a shop evacuate the system before you begin any repairs.
You can fix the AC in your vehicle yourself and save lots of $$$ just educate yourself beforehand and soon you will be cruising in a nice cool air conditioned vehicle!!
R12 in air conditioning systems was phased out before the vehicles in this post were built. GM used R134a ever since 1996, the vehicles this forum post about were made 2002-2009
 
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