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  #16 (permalink)  
Old 07-15-2008, 10:17 AM
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several things I did...

1] if you lost 8" of vacuum in 2 hours you have a leak....

2] drain all the oil out of all parts of the system... one of the biggest things I find is Oil-slugged systems... too much oil will decrease cooling capacity greatly.

3] replace the stock condensor with a parallel flow unit.. *AND* locate it closer to the radiator... GM is notorious for Locating their condensors far away from the radiator so esp in stopped idle traffic the fan pulls air in from everywhere but through the condensor.. you lose a lot of slow-move cooling this way...

4] I outfitted my system with a Sanden Compressor instead of the junky GM R-4 (radial) unit... the R-4 compressor was never designed to operate effectively with the higher head pressures R-134a produces esp in traffic.. - you lose performance...

I also found that hotrod air sells a pulley set in which the A/C grooves on the crank / waterpump pulley are slightly larger

5] I went to a GM yellow / white orifice tube.. it was between the GM white and the ford blue....

6] im running ES-12a industrial refrigerant... yes it is HC based... Yes I've been using it for years... and to the nay sayers.. I had HC-12a in a 1985 Cadillac in which I was Hit head on.. smashed the caddy all the way back to the firewall.. the A/C was in operation at the time... no fire....

at idle in my 86 Monte carlo in 90+ humid heat im typically blowing 42-46 degree air out of the vents on high speed fan.... out on the highway it easily drops to 38 or so where i have the compressor cycling out.. and it cycles out a lot so im nowhere near eating up the capacity of the system....

but the main things are these: efficient condensor. compressor made for 134a.. dont over-oil, and dont overcharge... 134a is very sensitive to overcharging....

-Christopher

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  #17 (permalink)  
Old 07-15-2008, 11:17 AM
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It is a known fact that R134a does not cool as well as R12, but that fact is greatly exaggerated most of the time by R134a foes. When I converted my 90 Chevy truck I actually thought the system worked better.

Vince
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Old 07-15-2008, 11:34 AM
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at HIGH RPM... 134a is shown to have a better cooling curve than R-12.. its just with Overdrive transmissions and all at cruise the RPM's arent high enough on the compressor to reach this curve....

Notice on the 04-06 Chevy silverados how small the compressor pulley is... also notice how nice and cool they stay.. the newer compressors can take higher revs than the older ones and with computers controlling compressor operation a simple shutdown of the A/C preserves the compressor life from an over-rev situation..

I havent been under the hood of any of the 07-08-09 chevy trucks to see if they use the dsame small pulley as earlier years or not...
-Christopher
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  #19 (permalink)  
Old 07-15-2008, 11:17 PM
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Twice now I've seem mention of a different orifice tube being used. Is this recommended when converting from R12 to R134a?

Thanks for all the suggestions and explanations of what works for you.

Unfortunately, there isn't enough room for a much bigger condenser in my application. The R4 compressor will have to do as I've got a new one coming.
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Old 07-16-2008, 07:48 AM
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Quote:
Originally Posted by Overdriv
Twice now I've seem mention of a different orifice tube being used. Is this recommended when converting from R12 to R134a
Yes it is.

Vince
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  #21 (permalink)  
Old 07-16-2008, 08:42 AM
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Quote:
Originally Posted by 302 Z28
Yes it is.

Vince
OK, what size? The original white one is .072".
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Old 07-16-2008, 05:20 PM
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Quote:
Originally Posted by Overdriv
OK, what size? The original white one is .072".
I dunno, ask the parts people they should have the chart that says what it needs.

Vince
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Old 07-16-2008, 08:01 PM
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When I made my conversion to R134a it worked well when we switched to a Ford Blue orifice, which is .067".

Bruce
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  #24 (permalink)  
Old 07-19-2008, 11:48 AM
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Well I finally found the reason it wouldn't hold vacuum. One of my 30 year old hoses on my R12 gauge set was leaking where it threads onto the manifold. So, I sprung for a new set of gauges and hoses for the 134A stuff, only to find the charge hose won't fit my vacuum pump. So I fiddles with my old gauge set and finally got it all tight enough that the system with both gauge sets connected would hold vacuum as long as I wanted. It held 29" for about 16 hours so I think it's good to go. The system took the first can on the vacuum. And I put another can and 2/3 of another (about 32 oz I think) in and the high side was very high, around 380PSI. After a while it did come down to 325 and the low side was about 40. That at 1300RPM and setting in my driveway with both electric fans running. Duct temp never got below 65 deg. So I disconnected and went for a ride. After about 3 minutes on the road, 50MPH at 2000RPM the duct temp cooled down to 54 deg. When I got in town the duct temp came up to about 55 deg and stayed there. 85 degrees and very high humidity today. The engine heated up to about 200 riding around town. I don't think the cooling system is going to handle the AC on in traffic on hot days, but we'll see.

What does everyone think? Do I have the charge volume close? 325PSI sounds kinda high to me. I will check it on another day and see what it's doing.
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  #25 (permalink)  
Old 07-20-2008, 11:15 AM
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I guess that you are over charged.

ambient times two plus 15%, I think is the generalization.

85 x 2 = 170 x 115% = 196 psi

You also need to measure the delta drop= the inlet and outlet air temp drop across the evaporator coil. You should be getting 35* on maximum fan speed.
At 85* inlet temp you should be getting 50 or colder. not 65.

You might be overcharged and/or the condenser might be too small for 134.
No more heat than the unit is pulling now should not be taxing the engine cooling system.

134 systems require a high pressure cut off switch, that ususally cuts off @ 360 to keep from blowing the system. The 134 pressure curve goes high above 90* ambient and requires a massive condenser to keep pressures under control.

edited, added link

"It's ALL about HEAT and TEMPERATURE! At 90 degrees ambient, for R134a systems, look for about 200- 220 Pressures on the high side and about 25-30 Pressures on the low side at idle, ...
www.aircondition.com/wwwboard/current/44954.html - 25k - Cached - Similar pages

Last edited by ScoTFrenzel; 07-20-2008 at 03:04 PM.
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  #26 (permalink)  
Old 07-20-2008, 11:30 AM
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Quote:
Originally Posted by ScoTFrenzel
I have one car getting two condensors in series and Freeze12. Sucker WILL cool in traffic or else.
He-he, hotrodded air conditioning...gotta love it!

I love you guys!
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  #27 (permalink)  
Old 07-20-2008, 11:32 AM
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Quote:
Originally Posted by 4 Jaw Chuck
He-he, hotrodded air conditioning...gotta love it!

I love you guys!

You can not have too much condenser. Vintage Air agrees.

(actually I just want it to work as well as the 87 Plymouth Horizon's did. They had the best ac ever. Would pull 55* delta drop at idle on 100* day)
In fact, if I could find one now, that is what I would be driving for an economy car, 28 in town and 38 on the highway actual)
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  #28 (permalink)  
Old 07-20-2008, 02:53 PM
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google R134 pressures http://www.google.com/search?hl=en&s...ssures&spell=1

"It's ALL about HEAT and TEMPERATURE! At 90 degrees ambient, for R134a systems, look for about 200- 220 Pressures on the high side and about 25-30 Pressures on the low side at idle, ...
www.aircondition.com/wwwboard/current/44954.html - 25k - Cached - Similar pages

This site lists an r134 pressure chart: http://www.ackits.com/index.cfm?fuseaction=Chart

Low Side PSI, Evap Temperature (F), High Side PSI, Ambient Temp (F)
16-29 , 33-50 , 115-200 , 70-80
19-39 , 33-60 , 140-235 , 80-90
25-43 , 40-65 , 165-270 , 90-100
37-51 , 48-65 , 210-310 , 100-110

Last edited by ScoTFrenzel; 07-20-2008 at 03:08 PM.
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  #29 (permalink)  
Old 07-20-2008, 02:56 PM
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If you've installed an accumulator or receiver/dryer, evacuated, then opened the system again, the accumulator or receiver/dryer will be no good in a very short amount of time. One purpose of the accumulator or receiver/dryer is to absorb moisture form the inside of the A/C system. Maybe you noticed that there was a vacuum inside the new accumulator when you pulled the caps off of it to install it. They put a vacuum on it before shipping to make sure the desiccant inside is dry. Leaving the accumulator or receiver/dryer hanging around without the caps on it or installing, evacuating, then reopening the system ruins it. The accumulator or receiver/dryer should be the last thing you change after you're sure the rest of the system is okay and before the final evac and recharge.
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  #30 (permalink)  
Old 07-20-2008, 03:58 PM
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Quote:
Originally Posted by 4 Jaw Chuck
He-he, hotrodded air conditioning...gotta love it!

I love you guys!
http://yarchive.net/ac/politics.html

quote
You have heard about all the low-capacity (poor cooling), hoses/
compressors busting (hi pressures) of R-134a? R-134a has
a steeper pressure/temp curve than does R-12. R-134a has a
critical temp of 214F vs 234F of R-12. Portions of the condenser
may easily hit 214F, at which point the R-134a will not liquify
at all or very little ... leading to poor performance in
stopped traffic/low air flow periods.


R-134a needs a much larger condenser due to this, and it located
away from the radiator (may not be possible), and beefed up
radiator fans
to suck in more cool air than for R-12. Retrofitted
R-12 systems are not likely to have large condensers/more air
flow.. so they will have very poor low speed/stopped performance.
quote

> the pressure/temperature curves of R-134a are so different from R-12,
> plus the excessive pressures generated on the high-side of the system
> may damage components designed for R-12.
>
> --
> Stephen Lacker
> Applied Research Laboratories, The University of Texas at Austin
> slacker@arlut.utexxas.edu (Remove the extra 'x' to mail me)

Last edited by ScoTFrenzel; 07-20-2008 at 04:22 PM.
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