Chevelles.com banner

61 - 78 of 78 Posts

·
Premium Member
Joined
·
13,602 Posts
When you turn the fan speed down, you'll get lower vent temps, give it a try and see what you get!!
 

·
Registered
Joined
·
315 Posts
Discussion Starter #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:
 
  • Like
Reactions: LeoP

·
Registered
Joined
·
315 Posts
Discussion Starter #63
When you turn the fan speed down, you'll get lower vent temps, give it a try and see what you get!!
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
 
  • Like
Reactions: LeoP

·
Registered
Joined
·
315 Posts
Discussion Starter #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
 

·
Registered
Joined
·
315 Posts
Discussion Starter #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.
 

·
Premium Member
Joined
·
6,004 Posts
You should have left it alone yesterday!!
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
 

·
Registered
Joined
·
315 Posts
Discussion Starter #68
He messed up long before yesterday. It was the day he pulled the Schrader valve when he installed the POA into the system.



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
Thanks Al ! I finally really understand how the system works. :nerd: Yes, I always wrongly assumed that the freon flowed the opposite direction than it really flows. :confused: I also wrongly assumed that if there is no way to mechanically press open a schrader valve, then, it will never open -- wrong -- vacuum will open a lightly sprung schrader valve. I see now that the vent temps will still depend on how efficient the Condenser is, but, it seems to me, at idle (950 rpm) with the Schrader check valve in place, I will get more liquid freon going to the Evaporator which may even further stabilize my idle vent temps.. I will publish new numbers when I get it fixed.

By the same token, I also believe I installed my POA eliminator incorrectly in the past. Since there is no POA valve to stop the freon flow in a POA eliminator, there is no need for the oil bypass hose. It seems to me if I blocked off the oil bypass hose with the POA eliminator, I would have had better performance with that setup.
 

·
Premium Member
Joined
·
6,004 Posts
By the same token, I also believe I installed my POA eliminator incorrectly in the past. Since there is no POA valve to stop the freon flow in a POA eliminator, there is no need for the oil bypass hose. It seems to me if I blocked off the oil bypass hose with the POA eliminator, I would have had better performance with that setup.

I think that oil return line is important in both systems to remove oil from the bottom of the evaporator to prevent oil logging of the evap. On the POA eliminator each time the compressor stops the refrigerant has a chance to pool in the low spots, the evap being one of them. Too much oil here cuts down on EVAP efficiency.

When you start your recharge, charge by weight. When you get close to having a full charge watch your low pressure side. I think your best vent temps will now come in with about 30 psi or slightly less on the suction side. I can see adding the Schrader valve will improve vent temps a bit, but think you'll still see a slight drop off in performance at idle. We shall see.

For some reason, I thought you were running electric fans, but now I see you are running the stock fan set up. To me, that's a good thing. You should be running the 772 fan. Hayden makes a HD and severe duty fan clutch, these will come on sooner and also offer more flow at idle. Not 100% sure they are available for this application. The cost is more noise and less fuel efficiency. The payoff is more flow through the condenser at idle. Bob, Robinls5, is a big fan of the late model Suburban fan clutch. Personally I think your numbers are fine, but these parts are another step up to chase that Dragon you've been chasing.

I wish you would have asked about the Schrader valve before you removed it. It's been 10 years since I installed a POA eliminator kit, I'm trying hard to remember if it had the LP SCHRADER valve in the oil return line, I 'm pretty sure it did, but not 100% sure. If someone has one on a shelf maybe they can check it out for us???
 

·
Registered
Joined
·
315 Posts
Discussion Starter #70
I think that oil return line is important in both systems to remove oil from the bottom of the evaporator to prevent oil logging of the evap. On the POA eliminator each time the compressor stops the refrigerant has a chance to pool in the low spots, the evap being one of them. Too much oil here cuts down on EVAP efficiency.

When you start your recharge, charge by weight. When you get close to having a full charge watch your low pressure side. I think your best vent temps will now come in with about 30 psi or slightly less on the suction side. I can see adding the Schrader valve will improve vent temps a bit, but think you'll still see a slight drop off in performance at idle. We shall see.

For some reason, I thought you were running electric fans, but now I see you are running the stock fan set up. To me, that's a good thing. You should be running the 772 fan. Hayden makes a HD and severe duty fan clutch, these will come on sooner and also offer more flow at idle. Not 100% sure they are available for this application. The cost is more noise and less fuel efficiency. The payoff is more flow through the condenser at idle. Bob, Robinls5, is a big fan of the late model Suburban fan clutch. Personally I think your numbers are fine, but these parts are another step up to chase that Dragon you've been chasing.

I wish you would have asked about the Schrader valve before you removed it. It's been 10 years since I installed a POA eliminator kit, I'm trying hard to remember if it had the LP SCHRADER valve in the oil return line, I 'm pretty sure it did, but not 100% sure. If someone has one on a shelf maybe they can check it out for us???
Thanks Al, yes, I also wished I asked you about the LP Schrader valve... :clonk:

Yes, I am running the original stock 7 blade curved fan with the Hayden heavy duty fan clutch, NOT the severe duty.

When I got back from travel, I was low on freon.... I found the leak, the low side schrader valve on the POA was leaking, and the cap would not hold it back. I got a new cap with an o-ring and it holds pressure and "pops off" when I unscrew it, but, it looks like I will have to monitor this low side schrader valve --- I am hoping it will fix itself now that I got the cap to hold pressure...

Well, everything is ready now - LP schrader valve, and I believe I have roughly 46 oz of so of freon... Here are my new numbers this morning. I started with a cold car, 85 degree garage - than went up past 90 degrees after 15 min.. I ran two house fans on the condenser, started the Chevelle and ran it from cold start for 15 min... Engine was at 1500 rpm. I like my numbers... What do you think ?

Low side, high side, center vent temp.

32, 125, 48 deg
31, 125, 45 deg
29.5, 133, 43 deg
28.75, 133, 43 deg
29, 140, 42 deg.
30.75, 156, 43 deg.
31.5, 167.5, 44 deg
32.5, 167.5, 44 deg.
32.5, 170, 45 deg.
32, 170, 45 deg.
34.5, 175, 47 deg.

The garage was about 95 deg. after all this... about 10-15 min. of running. I then knocked down the RPMs from 1500 to 950 RPM and let it settle for a few min. This is what I got:

Car warm after 10-15 min. of running:

Idle - 950 rpm, low side - 38, high side - 167.5, center vent temp - 49 deg..

I am thinking I am pretty close..., what do you think about my numbers and the freon quantity ? Thanks.
 

·
Registered
Joined
·
315 Posts
Discussion Starter #71
I think that oil return line is important in both systems to remove oil from the bottom of the evaporator to prevent oil logging of the evap. On the POA eliminator each time the compressor stops the refrigerant has a chance to pool in the low spots, the evap being one of them. Too much oil here cuts down on EVAP efficiency.

When you start your recharge, charge by weight. When you get close to having a full charge watch your low pressure side. I think your best vent temps will now come in with about 30 psi or slightly less on the suction side. I can see adding the Schrader valve will improve vent temps a bit, but think you'll still see a slight drop off in performance at idle. We shall see.

For some reason, I thought you were running electric fans, but now I see you are running the stock fan set up. To me, that's a good thing. You should be running the 772 fan. Hayden makes a HD and severe duty fan clutch, these will come on sooner and also offer more flow at idle. Not 100% sure they are available for this application. The cost is more noise and less fuel efficiency. The payoff is more flow through the condenser at idle. Bob, Robinls5, is a big fan of the late model Suburban fan clutch. Personally I think your numbers are fine, but these parts are another step up to chase that Dragon you've been chasing.

I wish you would have asked about the Schrader valve before you removed it. It's been 10 years since I installed a POA eliminator kit, I'm trying hard to remember if it had the LP SCHRADER valve in the oil return line, I 'm pretty sure it did, but not 100% sure. If someone has one on a shelf maybe they can check it out for us???
Thanks Al, yes, I also wished I asked you about the LP Schrader valve... :clonk:

Yes, I am running the original stock 7 blade curved fan with the Hayden heavy duty fan clutch, NOT the severe duty.

When I got back from travel, I was low on freon.... I found the leak, the low side schrader valve on the POA was leaking, and the cap would not hold it back. I got a new cap with an o-ring and it holds pressure and "pops off" when I unscrew it, but, it looks like I will have to monitor this low side schrader valve --- I am hoping it will fix itself now that I got the cap to hold pressure...

Well, everything is ready now - LP schrader valve, and I believe I have roughly 46 oz of so of freon... Here are my new numbers this morning. I started with a cold car, 85 degree garage - than went up past 90 degrees after 15 min.. I ran two house fans on the condenser, started the Chevelle and ran it from cold start for 15 min... Engine was at 1500 rpm. I like my numbers... What do you think ?

Low side, high side, center vent temp.

32, 125, 48 deg
31, 125, 45 deg
29.5, 133, 43 deg
28.75, 133, 43 deg
29, 140, 42 deg.
30.75, 156, 43 deg.
31.5, 167.5, 44 deg
32.5, 167.5, 44 deg.
32.5, 170, 45 deg.
32, 170, 45 deg.
34.5, 175, 47 deg.

The garage was about 95 deg. after all this... about 10-15 min. of running. I then knocked down the RPMs from 1500 to 950 RPM and let it settle for a few min. This is what I got:

Car warm after 10-15 min. of running:

Idle - 950 rpm, low side - 38, high side - 167.5, center vent temp - 49 deg..

I am thinking I am pretty close..., what do you think about my numbers and the freon quantity ? Thanks.

PS. Do you think my POA valve is set too high ? It seems to be set at 28.5 psi low side.... I expect it to be set much lower ? maybe, 20 psi for R134a ?
 

·
Registered
Joined
·
315 Posts
Discussion Starter #72
I just went for a 10 min. ride in the sun with 102 deg. heat with the fan on high. The best I could get in the city was 58 deg. out the center vent. This was cruising in 4th gear at 2K rpm. At idle which was 850 rpm, it would creep up to 65 deg. in 3 min. On the fwy, I believe it will cool down 2 to 3 deg. more, so, mid 50's would be best in 102 deg. heat. It's not horrible, but, I am not satisfied. I will take the next steps to improve....
Ok, this is one of my previous posts in this thread before the upgrade. I just made the same run and the temperature here is the same as it was then 102 degrees. The best center vent temperature I could get with the same run as before is 48 degrees. Most of the time is was around 50 degrees. At idle, it crept up to 53 after 2 min.. So it looks like I dropped the temps 10 degrees, but, I am also moving more air volume (clean evaporator and suit case), so, if I move the fan to 3/4, it will get me another 2 or 3 degrees, so, we could say it improved my vent temps up to 13 degrees. Idle temp was a big upgrade. Now, you cannot really feel a difference in temperature at idle even though the center vent temps climb up 3 degrees or so. Does this seem about right ? Thanks.
 

·
Premium Member
Joined
·
6,004 Posts
PS. Do you think my POA valve is set too high ? It seems to be set at 28.5 psi low side.... I expect it to be set much lower ? maybe, 20 psi for R134a ?
The builder that supplied your POA say he sets the POA valve for 20 psi for the r134 system. I'm not seeing that in your pressure recording. Your POA is showing pressures for one set to run r12. Yes, this could be causing higher vent temps. The consensus up until I heard of the 20-degree setting, was to set the poa for 134a at 26psi. Look at the PT chart and you will see that at 32 degrees, the pressure is 27.8 for 134a. The consensus and results showed that running a slightly lower number of 26psi made up for inefficiencies in heat transfer between the air and components and would prevent freeze ups in most conditions. Also note that r12 was set at about 29-30 from the factory because water will freeze at 32 degrees and that was just below the numbers on the PT chart for the same reasons.

I was very interested in seeing the results of a POA set at 20 PSI. Your vent temps should be lower, but you may experience evaporator feeze ups because water freezes at 32 degrees. Your evap is constantly pulling moisture from the air. You can witness this by the condensate flowing from the evap drain. Under certain conditions, the air entering the evap is not warm enough or there is not enough flow to keep the moisture from freezing up the evap. The factory also installed the ambient temp switch in the suitcase to cycle the clutch should temps register below 32 degrees in the suit case. That means the air temp when achieving 32 degess would shut down the compressor. The flow of hotter air in the system would allow lower poa settings and lower evap temps than 32 degrees until it began to freeze up and flow slowed to the point where the air in the box reached 32 degrees, the comp would shut down until the temps again were within spec.


When 134a conversions were all the rage, we were testing and setting our own poa pressures before each installation. I would use the 26 psi setting because at the time it was the consensus and I had to get it right the first time because back then I didn't have a recycling machine to make experimenting cost-efficient. You purchased through a reputable rebuilder so I never thought to test the poa pressures. Guess we need to check even the work of the pros in the industry.

To properly set a poa valve the system must be discharged and opened again. You can test basic function of poa by disconnecting the blower motor and running the system on max. Initially, the reading you see will be the set point of the poa, then as pressures drop, the poa will function and start allowing more flow into the lowside of the system to prevent freeze up. This will show a corresponding rise in low pressure side as the poa attempts to prevent lower pressures that will freeze up the evap.


I had to work a double yesterday, on a Saturday, and your answer required more than a few drive by sentences for a reply. I was beat yesterday and all I had left was a few drive by posts.
 

Attachments

·
Registered
Joined
·
315 Posts
Discussion Starter #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.
 

·
Registered
Joined
·
315 Posts
Discussion Starter #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.
 

·
Registered
Joined
·
315 Posts
Discussion Starter #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.



 

·
Registered
Joined
·
315 Posts
Discussion Starter #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:
 

·
Registered
Joined
·
315 Posts
Discussion Starter #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:
 
61 - 78 of 78 Posts
Top