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Discussion Starter · #1 · (Edited)
So I pretty much got all the New AC components installed and now ready to evacuate the system and charge it up.

I was going to bring it down to my local shop to have them do the evacuation and charging but since I’m not confident that my lines are all sealed properly I was thinking that maybe I should get the vacuum pump and gauges at Autozone as a loaner and see if the system will hold a vacuum? Do it myself….it seems simple according to YouTube but can I screw it up?

So… these two high and low 134a ports (see pic) are the two that hooks to the gauges plus the yellow vacuum line to the pump? Right?




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1988 Ford Bronco XLT 5.0 four speed auto Raven black with red interior
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Yes. the hoses are color matched Blue hose goes to the blue capped suction or low pressure line and the red hose goes to the red capped line or high pressure line. Yellow line to the vacuum pump Turn on pump and open up gauges to pull vacuum on system. I always pull a vacuum for a few minutes and close everything down and turn off the pump. let the system hold the negative vacuum for 30mins or so to make sure there's no leaks and then run it for at least 30mins or so to make sure all moisture is out of the system. Turn it all off again, leave it sitting for a few mins to make sure of no leaks and then charge to what factory calls for in vehicle.
 

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Good advice bandit704
While leak checking with the pump is somthing I do at times on a complete retrofit
I like to pressure test with nitrogen if it’s available to me. Pump up to 300 psi and let hold over night.
Then when proven leak free pull a vacuum for an hour or more. Overnight is best as longer is always better
Then weigh in the charge. Converting to 134a will require some math to get the exact weight
Or could charge by seat of your pants
Just be aware that under charge is better than over charge. Liquid to the compressor will destroy it.
also from experience I would add that a lot of times when chasing down a leak it turns out to be at the manifold gage set. Leaking fitting or hose !
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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The AC manifold gauge lines will only fit on the correct ports. One is quite a bit bigger than the other. Yes, yellow is the vacuum/refrigerant charging port.

Dont trust the gauge valves to be normal. One of mine opens by going CCW and the other CW. Both were labeled as CCW...
 

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Discussion Starter · #7 ·
Did not use leak lock. I followed the directions from the Original Air Group factory kit instructions.. I did make sure I lubricated all O Rings.

I do though need a little help with charging my new system with 134a. In the hopes that there are no leaks during a vacuum pull, how much 134a do I actually empty into the 78 bronco system? I found this conversion chart but unsure what to do? Thanks!
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First thing is to find the weight of the factory r12 charge. It’s some where under the hood on a name plate unless someone removed it over the years
I believe it was 2 3/4 or 3 pounds
Do you have a sight glass in the liquid line?
 

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Discussion Starter · #9 ·
Thanks Gondal.....The Original Air Factory AC replacement does away with the sight glass. I found a 1978 Bronco?Truck specification booklet I purchased on eBay a while back. It indicates a capacity of 2 pounds for R12. So since this is a 134a system now do I just calculate 80% of 2lbs? See pic...
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1986 Bronco Eddie Bauer 5.0 mostly stock
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First thing is to find the weight of the factory r12 charge. It’s some where under the hood on a name plate unless someone removed it over the years
I believe it was 2 3/4 or 3 pounds
Do you have a sight glass in the liquid line?
Looks like he had an aftermarket system put on, i see "classic auto air" on that compressor, they should be able to tell you how much refrigerant you need. Otherwise you'll need to add it by reading the gauges between cycles on both low and high sides. I know my 86 with factory AC takes 54 oz of r12 and that equates to about 43 oz of r134 (3.5 cans).

Also, as mentioned, pulling a vacuum is a critical step to remove the moisture out of your system. The longer the vacuum the better, you want to pull the system down to about -29.5 on your blue gauge. It took me about an hour to do that on mine the other day. You also need to make sure when you pull the vacuum you leave the pump running while you close the valves on the gauges, but leave the valves open at the nipples so the gauges will read if you have any leaks. If you do this right you can pull nearly a whole can into the system before you crank it up. Oh yeah, and only use the low side when you're adding refrigerant, just shut the high side off. You may have to jump your pressure switch until you get enough juice in there for it to operate normally.
 

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80% of two pounds shows as 25.6oz, which is one full 16oz can and a 9.5oz of another. Use a scale to weigh a full can, subtract 9.5 oz and that should tell you when to stop on the second can.
 

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Robzz28 is right. Check with the manufacturer
that should put you in the ballpark

if you are not happy with their answer or they don’t answer all

put in the 80%. Drive it down the highway
As you need air across the condenser to get the coldest air at the vents.
It will never be super cold at idle unless you have a big auxiliary fan on the condenser
Then if not cold after driving about 5 minutes at 30 mph or more add 4 oz at at time until it’s cold
Charging an AC is not as simple as it takes 5 quarts of oil. It just is not that way
The factory charge often times needs adjusting
Just remember over charge will ruin it fast
 

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Discussion Starter · #13 ·
Yes it’s a Classic Auto Air / Original Auto Air …..same company. The Original Auto Air systems are designed to fit a truck where there were no modifications to the Layout. All they tell you is to find out the the R12 capacity as it came from the factory and use the chart to convert to a 134a system. I’m a little confused it’s the last three columns of 134a percentages….



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If that's the case, then i would put two 12 oz cans in there and see where you're at. Check your temp at the vent with a thermometer and if it's not at least down in the 40's id add the extra 1.6 ounces.
 

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Start with the lower % first Add as needed
You will know when it’s close when you have a cold suction line at the compressor
A compressor can not compress liquid. So again don’t over charge
 

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Discussion Starter · #19 ·
Such great advice! Do you put the leak detector dye stuff in the system?


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Going on 22 years in the hvacr service construction trade
I do not recommend dye
The oil in the system will act like dye just harder to see
I don’t believe in putting dye or other things like stop leak in the system. It’s just snake oil in my opinion
If you pressure test before vacuum and fix any leaks now you will have many years of leak free cooling
Pump to 300 psi with nitrogen. Let it stand for 24 hours. If pressure is not lost you are golden
I highly recommend leak lock, or refrigeration lock tight on the threaded fittings.
 
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