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r134a numbers with stock Condenser & replacement POA

10K views 77 replies 9 participants last post by  hjdca 
#1 ·
Hi Guys, I have my Chevelle converted to R134a with the replacement POA, Sanden Compressor, stock Condenser, & new Dryer. In 100 deg. temperatures, the best I can get on the fwy is 55 deg. out of the center vent. At idle, 925 rpm, it reads up to 65 deg. out of the center vent in 100 deg. heat.

When starting the cold Chevelle in 90 degree weather in the shade at 1400 rpm, here are my r134a readings with no fan upfront. I am running the stock clutch fan. What do you think about these numbers ?

At cold startup to around 10 min. to warm up.

Low side High side
44 155
43 155
42 170
44 175
48 185
50 195
52 200
53 210

Of course, the air in the car is much colder at first startup and the air gets warmer as the Chevelle warms up.

I am thinking I need a new parallel flow condenser from original air to get lower temperatures. What do you think ? Thanks for any advice.
 
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#52 ·
Great job Harry. I'm glad all your hard work finally paid off.:thumbsup::thumbsup::thumbsup:

Pressures look good after you removed some freon. What's most telling is your vent temps. Lookin good. Try running on a cool morning with the fan on low speed and watch your vent temps.
If they drop below 35* you'll want to hook up an ambient temp switch to avoid ice ups of the evaporator. If you see cool vapor coming out of the vents, you're getting into ice up territory.

Your pictures made this thread a keeper.
 
#53 ·
Thanks Al, I am very happy. My girlfriend and I took a 66 mile (33 miles each way) drive to Bob's big Boy Car show. It was over 100 deg. out when I left and I was getting 49, 48 degrees out of the center vent on max. high. We were very cool in the Chevelle, even in traffic. On the way home, at night, I got 37 deg. out of the center vent on max. high. My girlfriend complained a few times that she was freezing. I am also getting a lot more air volume on high which cools you off a much faster. Honestly, this work completely changed my car. I moved my high idle ( with air cond. on) to 950 rpm, and my normal idle stays at 850 rpm. This seems the sweat spot. Thanks again for all your help ! :thumbsup::grin2:

PS. Plenty of water coming out of the bottom of the suitcase and condensation on the cold lines and POA.
 
#54 ·
i would be pretty happy with those vent temps. I have peeked in my suitcase through one of the switches mounted on top. it looks pretty clean, but i know deep down inside theres many many years of crud in there, which im sure is why air flow through my vents is weak.
 
#55 ·
Yes, probably... I was one of those guys that went through all my vents, loosened the other side of the suit case, and replaced my blower motor, then fished my air compressor line in there and blew some stuff around. Afterwards, I went from "high" blowing on "low" to "high" blowing on "3/4". I felt pretty good and called it done. My suitcase is "clean". Note: the stock air cond. blower motor has a different part number than the stock non-air cond. blower motor. The former is more powerful, so, you want to make sure you get the right one for Air cond...

But, now that I actually took the system apart and was able to get the Evaporator out, replace it, and clean out the suit case, I can say, that this seems to be the most important part of the process. The new air flow amount on "high" blows on "super high". There is a big volume difference between 3/4 and "high" now, and that makes a big difference in cooling off the back seats and how fast the passengers cool off when the car has been in the sun. I have to say I am pretty surprised. I did not expect it.
 
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#56 ·
On my 70 Sta. Wgn. I have a water shut off valve. ( LOWES ,& painted black). I have it close to the firewall. Now no worries about heater doors or some flappers not sealing well or radiant heat that may impact the evaporator.
Another item, 70 owners & others.........." LOOK " at the---- SPACE---- between the Rad. tanks & the core support. I bought some Black foam tape with the sticky back side. 1" X 1" or 3/4" X 3/4".... Slide the foam tape in place then with needle nose, Pull the tape covering.
WHY?........ When you are going slow or near a static position, With "" NO "" outside air pressure pushing air into the engine bay, The engine powered fan blade will pull this super heated air ( from the engine bay) through this large gap, AND... Right back into the ALREADY HOT, AKA " Heat Exchanger " or Rad.
Blocking this airflow passage will drop your Temp,,by 3 to 6 degrees.
Be KOOL and have fun!
Bob
 
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#57 ·
Ok Bob, you managed to get me motivated again. You guys have not steered me wrong yet. I have a bunch of high and low density foam strip in that size. Here is a pic, is this the area you are talking about ? The space between the Aluminum radiator and core support - yes, roughly 3/4".
I should have done it from the front when I had the condenser out, it would have been easier to position perfectly on the passenger side where the battery tray is in the way -- new tip for everyone, lol ---:surprise:. Well, I have the foam, so, I will try it. I think I will try the high density first. Thanks again.

 
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#58 ·
If you decide to adjust your pressures, make sure you bleed your gauge lines every time you hook up or you risk introducing air into the system.

Bob's recommendations of sealing the evap to the radiator are spot on and I think will help even more if you are using electric fans because it forces the fans to pull through the condenser which would help at idle. Removing the rad top plate will allow you more room and a way to seal the top. On the bottom just push in some sort of insulation.

The positive heater shut off valve is also a good recommendation because the stock heater valves always seem to leak some hot coolant through the system.

I wish I would have been here before you got to the point of charging, I would have given some more advice on charging the POA system. My real job got in the way.:angry:

Your pressures may still be a bit high, but hard to determine when you are running the car in a garage. I figure the garage temp is much higher than the ambient temp due to the heat generated by the running engine. So that's possibly throwing off your pressures and causing them to read a bit higher. You can tell if your cooling airflow is affecting the vent temps and pressures by running water over the condenser, but that can make a mess of your clean engine. I run 2 big fans into the condenser while charging to help cool the condenser. Even with this, I'll see a drop in head pressure when I run water over the condenser, so at some point, you call good enough.

Your temp increase at idle is likely due to lack of airflow and your pressures are going up. If your pressures go down at idle, it may be due to the smaller displacement of the a/c compressor.

When charging the POA SYSTEM I watch the recommended charge quantity and the vent temps carefully. When I get close I take the time to add refrigerant slowly and watch the pressures and vent temps. You'll notice a point where both gauges will start to climb and vent temps go up. Charging slowly at this point is key because the system needs time to stabilize after adding refrigerant.

Your vent temps may benefit in a reduction of pressures, The POA system dumps excessive pressure to the low side to keep the TXV pressure constant. The increase in lowside pressure negatively affects cooling performance. So like an engine, tuning a Frankenstein A/c system is a tool for best performance. With the factory system, the factory already did this for us and we charge by weight.
 
#59 ·
Ok, I put 3/4 inch high density foam in, but, I recommend 1 inch instead. I think I will switch mine to 1". I used my cheap grab tool to set the line. Here are some pics:






I put the two big house fans in front of the Chevelle and ran some tests from cold start. My gauges are still charged with freon, so, no worries about air in the system. Here are my results.

Engine off - low side, high side - 92 psi, garage temp 93 deg. ambient.

engine started:

low side, high side, vent temp, approx. time
34 psi, 148 psi, 49 deg. - 1 min.
32.5 psi, 152 psi, 47 deg - 3 min.
31.5 psi, 155 psi, 46 deg. - 5 min.
33 psi, 173 psi, 46 deg. - 8 min.
33.5, 188 psi, 48 deg. - 10 min.
36.5, 200 psi, 50 deg. - 12 min.

What do you think about the freon quantity ? The system tried to stay at 46 for a while, but, then, the pressure started going up and it could not maintain 46 deg... The times are approx... I noted down the numbers when I saw things start to change. It looks like the best numbers were 31.5, 155 with 46 deg. vent temp...
 
#60 ·
At the current ambient temps it looks like these numbers are your target.33 psi, 173 psi, 46 deg. - 8 min. to 33.5, 188 psi, 48 deg. - 10 min. Set here between these 2 and take a test drive to verify your work.

Vent outlet temps will prove you're on the right track when running down the road and getting good airflow through the condenser and steady output from the compressor. If your vent temps rise on the road, it puts you back to not having sufficient charge and your stationary issues are condenser temps/lack of airflow. It appears your compressor has plenty of output to supply the needs of the system. I actually expect to see temps in the lower 40's going down the road. Maybe that heater control valve is not doing its job. This will affect temps at cruise and at idle as your coolant heats.

Your static pressure is right on. It shows about 1 psi for each degree in temp. All that really shows is that the system is does not have air contamination or refrigerant cross contamination and you have enough to trigger the low pressure switch. The state of charge must be read with the engine running.

The pressure building is a result of heat in the system and lack of airflow through the condenser. Might even be related to heat building in the garage. There's only so much you can do here and you've done or are doing all you can short of higher flow cooling fans. At some point, you can continue to chase the dragon or call good is good. As this crazy humidity we've been having here diminishes to regular levels, so will your perceived cooling from the a/c unit.
 
#63 ·
yes, I can consistently drop approx. 3 degrees vent temperature going from high fan to 3/4 fan. So yesterday, when I was rocking 43 degrees on the fwy on high fan, I could drop the vent temperature into the 30's going to 3/4 fan speed. That is a nice feeling. :D
 
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#62 ·
OK, you are right again. some better numbers on max air setting. I recovered some more refrigerant, 1 or 2 oz. I think, and my vent temps. were great today. It was 98 degrees today and I was consistently 47, 48 degrees all day driving around. On the fwy, in overdrive, at 70 mph, I managed 44 deg., and an occasional 43 degrees - just like you said. Idle vent temp still rises but way slower than before. I mean, if you are at 47 deg. vent temp, and you hit a long light, it may rise to 50 vent temp, something like that.

PS. I had the sniffles this morning. yea ! :wink2:
 
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#64 ·
Ok, I put in high density foam - 1/2 by 1/2 on the top and sides of the radiator. I also recovered a few more ounces of Freon. As Al predicted this stabilized my idle temperatures. I only had a chance to test tonight in 75 degree weather, but, I was able to cruise around town in the low 40's vent temperature, then, sit stationary for 4 min. without going above 45 deg. vent temperature. I am happy, and I think I am done with the job. Thanks to this forum, for the guys that gave me all the help, to make my Chevelle Kool again. :thumbsup::D
 
#65 ·
Update :surprise::surprise: - Last night, I saw half my POA with condensation on it and the other half without (the half going to the evaporator). Then, I remembered that weird red schrader valve that was in my new POA oil return line fitting... My old POA eliminator did not have it, and there did not seem to be anything to push it open, so, I took it out and forgot about it. Well, I just read about it, and I realize that it is a very light spring schrader valve that works on vacuum. I tested the valve with my finger and sure enough it is way, way lighter spring than a normal schrader valve. I think I am getting reverse flow from not having the schrader valve in there working properly and this is increasing my freon temp before it goes into the evaporator.

I am going on work travel for a few days, but, when I get back, I plan to fix it. Do you guys agree that this fix should give me better vent temps, or should I just leave it out ? Thanks.
 
#67 ·
He messed up long before yesterday. It was the day he pulled the Schrader valve when he installed the POA into the system.

Update :surprise::surprise: - Last night, I saw half my POA with condensation on it and the other half without (the half going to the evaporator). Then, I remembered that weird red schrader valve that was in my new POA oil return line fitting... My old POA eliminator did not have it, and there did not seem to be anything to push it open, so, I took it out and forgot about it. Well, I just read about it, and I realize that it is a very light spring schrader valve that works on vacuum. I tested the valve with my finger and sure enough it is way, way lighter spring than a normal schrader valve. I think I am getting reverse flow from not having the schrader valve in there working properly and this is increasing my freon temp before it goes into the evaporator.

I am going on work travel for a few days, but, when I get back, I plan to fix it. Do you guys agree that this fix should give me better vent temps, or should I just leave it out ? Thanks.
Fix it. During periods when the valve throttles, the Schrader opens and supplies oil to the suction side to the compressor. Right now it's acting like a second TXV valve and dumping liquid refrigerant into the Poa valve. The oil pickup tube is the lower section of the evap where the liquid refrigerant is still in the process of turning in to a gas. Right now the liquid is turning into a gas at the point where you see the frost due to the pressure drop.

I'm not sure that it will affect vent temps because the other controls might be able to compensate for the bypass of refrigerant, but I expect to see slightly lower suction side pressures. Yours are bit high for a POA system, but your vent temps were not that far out of line. So it faked me out by indicating a slight over charge due to the higher than expected suction pressures.

Fix it, we'll find out.

It's not unusual for a POA valve and the return lines to become frosty, this means the POA valve is doing its job and holding your set pressure and dumping the rest to prevent freeze ups. This means in the conditions the a/c is currently running, the added cooling capacity of the system is not needed and being dumped in the low side to prevent freeze-up of the evap. Icy suction lines
and return lines are common at light cooling loads with a POA in place and functioning as designed.

By the way, the POA valve is in the suction side of the system leading FROM the evaporator, not leading to it. It regulates pressure from the evaporator and keeps it from going below the set point. The TXV valve is the in side of the system where the high pressure leads into the evap
 
#74 ·
Hello Al, thanks for all your efforts. I really appreciate it.

I fixed my leaking POA R134a POA schrader valve using a tool that saves the freon. The damaged schrader valve was my fault, I damaged it when I test fitted it to the POA which already had a schrader valve in the R12 fitting. I noticed it, and removed the the R12 schrader valve, but, the damage to the R134a schrader valve was already done and I did not notice it. Note: you have to lower your hood to 1/3 open and prop it there, to clear the hood hinges and spring, if you are replacing the low side POA schrader valve using a tool that saves the freon.

I also found that my vacuum pod was not completely opening my vents. I was getting air diverted to the floor and defroster. I got that straightened out and now I have all the air going to the front vents. As you can imagine, I am getting tons of air volume now. Pretty close to a modern car.

I took a night drive with the new fixes and I got a low of 36 degrees out the center vent on high and max air. I remember getting 37 degrees on another warmer night a few days ago. So, it seems my POA is set to get me 36 degrees at its lowest low side setting at max air. 36 deg. maps to 31 psi cutoff on your chart, so, subracting for heat loss in the system, it looks like the POA could be set much lower - 26, 27, or --- 28.5 which is the lowest PSI I saw on the gauge, but, I was at 43 degrees in the garage when I recorded that, so, does 36 degrees center vent temp indicate a lower POA cutoff - ie. like 26 or 27 psi ?

What do you think ? At any rate the system is performing well, but, I want to extract the full benefits if I can.
 
#75 ·
Ok, I talked to Original Air in Tampa. He told me that my numbers are consistent with a POA R134 setting of 20 PSI. He said It is extremely difficult to get the low side to 20 PSI in the garage. He said this is validated by the fact that I can get 36 degrees at my center vent in cool conditions (70-75 degree ambient temp). He also said that 42 degrees at the vent usually means 36-38 degrees at the evaporator. He also said that if the POA was set for R12, I would not see better than high 50's degrees at the Center vent.

Now that I fixed my suitcase air leaks, my two schrader valve mess ups, and my air diverter issue, I will hook up my gauges again today (they are still full of freon), with my new higher airflow, to see where I am at and report back. Thanks again.
 
#76 ·
Latest test - I ran from cold start with 2 house fans in front of the condenser. These two fans are still not as good as a box fan. It was 82 deg. in the garage when I started, engine at 1400 rpm. This is the best numbers I got before things started to heat up. Check pics - low side 27.5, high side 138, center vent temp - 40 degrees. Based on these numbers I added 3 or 4 oz of R134a. High side seemed a little low, so, I figured I could use a few more ounces. I think I am pretty close. I was glad to get down to 27.5 on the low side.



 
#77 ·
I think I finally caught the Dragon ! >:) Proper R134a content was the key to final success. :nerd: My car is best with less than 48 oz. of R134a. Like mentioned in this forum before, I recommend you only put in 36 oz., then, drive around on a hot day and record your center vent temps on max high and add 2 oz at a time until you get your best temps.

Today, it was in the 90's here, and I was at 40-43 center vent temp cruising around all day. I also got some 39 degree readings. In addition idle center vent temp rises much slower and only 3 degrees or so. :smile2:

I am pretty happy right now.:grin2: It was not easy, but, it worked and I have one of the Koolest Chevelles around. Thanks Guys - (Al, Bob, Leo, etc..., actually, the whole board helped me !). What a great bunch ! :thumbsup::hurray:
 
#78 ·
New Update -
I replaced my heater control valve with a NOS GM, made in USA, heater control valve with the "bottle cap" seal that I bought on ebay. I tested it before installing it, and at 4 - 5 in hg., it completely blocks all passage of air or water.
I installed this valve, and used high density foam to seal the bottom of the condenser. I also added a reproduction rubber evaporator drain, mine was missing.
I re-did the placement and wrapping of my expansion valve bulb temperature sensor. I found this old 1968 GM stock photo, attached below, and my bulb is exactly the same, so, I set mine up exactly like that with two small hose clamps and only wrapped the part overlapping the suction line.



It has cooled off here. It was 75 deg. today and sunny. I went for a ride and the best I got was 29 deg. out of the center vent on max. high. at cruise. Mostly, center vent temp hovered around 31 deg. at max. hight, and idle was great - stabilizing around 37 degrees after about 3 min. on max high. It seems the system is working very good and the POA is also set correctly. The components seem top notch.

I think the only debate is my peanut sized compressor - Sanden SD7B10. I think it works fine in all conditions, but, in 105 degree heat, at idle, you would probably do better with a bigger compressor on the big stock Chevelle system. In my case, I prefer the compressor down low and not part of the showcase, so, that necessitates this small compressor, and I am happy with the cooling. :thumbsup:
 
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