Getting that factory AC going again. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ah_5500 · 09-01-2014, 09:03 PM

I decided it was time to get the original ac on my truck going. Everything is there and there are no leaks. So we pulled a vacuum and charged a couple cans of 134. I thought and partially assumed it had been converted from r12.
How do I know if it's been converted? How do I convert it if it hasn't?
The air got cold but pump started sounding and acting like it was about to lock up like it needed oil. School me on oiling please.
Lastly, the pump didn't cycle. It ran without shutting off.
Thanks in advance!

**VetteVet** · 09-02-2014, 01:06 AM

Here's some information to help you out.

http://www.google.com/custom?domains...D%3A1%3B&hl=en

joey8383 · 09-02-2014, 04:03 PM

Most people put the 134a quick connects on the lines when converted, although they are not 100% necessary. On the oil, when converting you should unbolt the compressor, dump all the old oil in to a measuring cup, then refill with PAG oil which is 134a compatible. If you were low on oil then just look up the oil capacity for the compressor. Dump the oil straight in the compressor through the suction line hole.
The compressor usually cycles on the low pressure switch when running. If you had the fan on high and the cab was hot, you were introducing a lot of heat in to the refrigerant in the evaporator and that causes the suction pressure to run higher. Most low pressure switches open around 15-20psig. You may have to drop the fan speed to see the suction pressure drop enough to open the low pressure switch.
The only method for charging a vehicle correctly is to weigh it in. if it holds 2 lbs, put in a couple 16 oz cans or similar after you pull a good deep vacuum.
In a pinch, I have topped off many cars by rules of thumb. Charge it up to about 35-45psig on the suction side (assuming a 75-80 degree cab and fan on high speed) and it will be close. That is the equivalent of about a 40 degree evaporator saturation temp and will get you close.
In my opinion, a lot of R12 condensers are too small for 134a. Look at a newer truck's condenser than compare it to our old R12 condensers. This will cause the refrigerant to not 100% condense and also cause high head pressure. If it doesn't condense completely you won't get 100% liquid to the metering device and you end up with a starved evaporator. Do you have a set of gauges to hook up to the truck where you can see suction and head pressure?

WhiteWhale · 09-02-2014, 04:19 PM

subscribed

ah_5500 · 09-04-2014, 10:41 PM

Thanks. Yes I have gauges. Just to be clear, which is high side and which is low side. I believe I had it correct but it doesn't hurt to be sure! I have found some r12 so I plan to pull vacuum and recharge with that.
I want to change the oil before recharging. What is your suggestion on oil to put back in? Amount? Thanks again

09-01-2014, 09:03 PM	#1
ah_5500 Registered User Join Date: Nov 2008 Location: knoxville, tn Posts: 155	Getting that factory AC going again. I decided it was time to get the original ac on my truck going. Everything is there and there are no leaks. So we pulled a vacuum and charged a couple cans of 134. I thought and partially assumed it had been converted from r12. How do I know if it's been converted? How do I convert it if it hasn't? The air got cold but pump started sounding and acting like it was about to lock up like it needed oil. School me on oiling please. Lastly, the pump didn't cycle. It ran without shutting off. Thanks in advance!

09-02-2014, 01:06 AM	#2
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,717	Re: Getting that factory AC going again. Here's some information to help you out. http://www.google.com/custom?domains...D%3A1%3B&hl=en __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

09-02-2014, 04:03 PM	#3
joey8383 Registered User Join Date: May 2012 Location: Okmulgee, OK Posts: 205	Re: Getting that factory AC going again. Most people put the 134a quick connects on the lines when converted, although they are not 100% necessary. On the oil, when converting you should unbolt the compressor, dump all the old oil in to a measuring cup, then refill with PAG oil which is 134a compatible. If you were low on oil then just look up the oil capacity for the compressor. Dump the oil straight in the compressor through the suction line hole. The compressor usually cycles on the low pressure switch when running. If you had the fan on high and the cab was hot, you were introducing a lot of heat in to the refrigerant in the evaporator and that causes the suction pressure to run higher. Most low pressure switches open around 15-20psig. You may have to drop the fan speed to see the suction pressure drop enough to open the low pressure switch. The only method for charging a vehicle correctly is to weigh it in. if it holds 2 lbs, put in a couple 16 oz cans or similar after you pull a good deep vacuum. In a pinch, I have topped off many cars by rules of thumb. Charge it up to about 35-45psig on the suction side (assuming a 75-80 degree cab and fan on high speed) and it will be close. That is the equivalent of about a 40 degree evaporator saturation temp and will get you close. In my opinion, a lot of R12 condensers are too small for 134a. Look at a newer truck's condenser than compare it to our old R12 condensers. This will cause the refrigerant to not 100% condense and also cause high head pressure. If it doesn't condense completely you won't get 100% liquid to the metering device and you end up with a starved evaporator. Do you have a set of gauges to hook up to the truck where you can see suction and head pressure?

09-02-2014, 04:19 PM	#4
WhiteWhale Registered User Join Date: Apr 2014 Location: Southern California Posts: 200	Re: Getting that factory AC going again. subscribed

09-04-2014, 10:41 PM	#5
ah_5500 Registered User Join Date: Nov 2008 Location: knoxville, tn Posts: 155	Re: Getting that factory AC going again. Thanks. Yes I have gauges. Just to be clear, which is high side and which is low side. I believe I had it correct but it doesn't hurt to be sure! I have found some r12 so I plan to pull vacuum and recharge with that. I want to change the oil before recharging. What is your suggestion on oil to put back in? Amount? Thanks again



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