Fixing A/C

[Edahall]

1990 Suburban with rear A/C.

There was a large leak in the system and turns out, it was coming from the high pressure pipe.  The pipe was leaking do to something rubbing on it. 

1.  The sticker says it needs 5.2 lbs of R-12 to refill.  How much oil do I need for a Suburban with rear air?  I guess I should drain all the remaining oil in it so I get the correct quantity.
2.  Where do I find the orifice tube?

[Da67goatman]

Mine says 5.25lbs, but mine's been empty for over 10yrs and it won't get filled for quite a while, so i can't tell you if its accurate or not.

[Lt.Del]

the rear part of the AC does not have an orifice tube.  There is an orifice tube in the line under the hood where the lines join near the battery.  There is an expansion valve in the rear ac unit w/ a temp probe that looks like a long wire.










Orifice is on high pressure line as it travels to the evaporator under the dash.  on our subs, it is after the condensor and after the receiver/dryer, follow the line a little further and you will see a joint, prior to going into firewall (to evaporator).

[Edahall]

the rear part of the AC does not have an orifice tube.  There is an orifice tube in the line under the hood where the lines join near the battery.  There is an expansion valve in the rear ac unit w/ a temp probe that looks like a long wire.

Thanks for the excellent pictures.  They are super helpful.  I actually did see that orifice tube but didn't know that's what it was.

Does the expansion valve in the rear AC need to be replaced?

[Edahall]

Mine says 5.25lbs, but mine's been empty for over 10yrs and it won't get filled for quite a while, so i can't tell you if its accurate or not.

Yeah, it was probably 5.25 lbs but isn't that just the amount of R-12?  If so, does anyone know how much oil I need to use?

[Lt.Del]

expansion valves do go bad.  I replaced both the exp valve and orifice tube in my sub when I overhauled the a/c a few years back.  I replaced compressor and dryer as well.  Always spend the $30 to replace the dryer when ever you open up your system and be sure to vacuum the system out completely many times--it boils under a lot of pressure and evaporates moisture within the system.   When replacing the orifice i found out it was placed in backwards by previous owner.

[Edahall]

Yeah, it was probably 5.25 lbs but isn't that just the amount of R-12?  If so, does anyone know how much oil I need to use?

Just for reference, the 90-91 Suburban with rear A/C uses 11 oz. of oil.  Without rear A/C it would use 8 oz.

Today, I blowed all the lines and components out to get as much of the old oil out as possible.  I also removed the compressor and tipped it upside down to drain the oil out of it.  How much of the oil did I actually remove using the method described? It sure didn't seem like 11 oz of oil came out.  Do I add 11 oz of oil or would it be less since there might still be some left in the system?

The reason I wanted to remove as much of the old oil as possible is because it has PAG oil in it which I've heard is extremely hygroscopic and simply putting a vacuum on it doesn't remove the water out of it.  There was a leak in the system for several years so it was exposed to the atmosphere.  The oil that came out looked clean and did not look milky but I wanted to be on the safe side.

[VileZambonie]

With the system open make sure you replace the accumulator. The rear system operates off of the front system with the exception of the rear blower control. I assume you are retrofitting it to R134A? The system should not have PAG oil in it. If it was an R-12 system it utilized mineral oil and would have a capacity of 9oz with an R4 compressor. You may also run Ester oil which I would recommend. Once you replace the accumulator and orifice tube, coat the o-rings with Ester oil. You can buy Ester with UV dye. Vacuum the system for at least 30 minutes. Charge the system with 8oz of Ester and then charge the system with 5lbs or R134A. Once you have completed the charge start and operate both systems and monitor your pressures. Top off if necessary according to your operating pressures, ambient temp & humidity.

[Edahall]

With the system open make sure you replace the accumulator. The rear system operates off of the front system with the exception of the rear blower control. I assume you are retrofitting it to R134A? The system should not have PAG oil in it. If it was an R-12 system it utilized mineral oil and would have a capacity of 9oz with an R4 compressor. You may also run Ester oil which I would recommend. Once you replace the accumulator and orifice tube, coat the o-rings with Ester oil. You can buy Ester with UV dye. Vacuum the system for at least 30 minutes. Charge the system with 8oz of Ester and then charge the system with 5lbs or R134A. Once you have completed the charge start and operate both systems and monitor your pressures. Top off if necessary according to your operating pressures, ambient temp & humidity.

It had already been converted to R134A several years ago and I think PAG oil is what is in it.  Is there a way to tell the difference between PAG and Ester oil?  Nothing was written down and PAG oil is what is usually sold during the conversion.

[VileZambonie]

You don't need to, just run Ester oil.

[Edahall]

I got it working this evening and it blows very cold.  The previous R-134a did not cool nearly as well.  I'm going to run it for a while then drain the oil out again and refill.