The LS swap A/C blues - Chevelle Tech
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post #1 of 71 (permalink) Old Jul 31st, 19, 8:54 PM Thread Starter
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neil
 
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The LS swap A/C blues

Hey guys Id like to pick your brains on an A/C issue Im having. I have a 72 Elco that I recently completed an LS swap.
Heres what I have:
original evaporator
new expansion valve
Old Air POA upgrade
r134a
denso 10s20f compressor
parallel flow condenser
trinary switch fed 12v from Old Air TCS switch(compressor on a relay and dual electric fans)

Heres what I don't have:
Comprehensive knowledge of A/C systems to diagnose problems

Heres whats going on:
Since this is an oddball system I have no exact numbers on how much to charge it so I went by the pressure chart. The problem I had with that is the pressures rise and fall with the fan turning on/off and the compressor on/off. I didn't know what pressure I was looking for. If I brought the rpm up to 1500ish the high side would go to almost 400 and it seemed like the low side didn't gain much pressure past 35 as I charged it. So I charged it as best I could and it was working pretty good. It was blowing 45deg about 80% of the time. Occasionally I would lose cold air for about 20 seconds when accelerating from a stop. I was afraid I may had overcharged it so I didn't use the AC much until I had a shop look at it. I took it in and they said I had overcharged it by about 8oz, they recovered the excess and told me to give it a try. The AC hardly works now. It generally works at idle and cycles from warm to cold at cruising. The shop thought that the trinary switch I put in was for r12 and was letting the compressor run way too high. The switch is for r134 and I cant find any switches available that would cut the compressor at a lower pressure. The high cut off pressure for all of them seems to be 375-400. The only thing I can think of is the expansion valve is not correct for my system and is not allowing proper flow? Like I said A/C is not my strong point. I get the basic concept of it but not much beyond that. Hopefully this post makes sense and If I can clarify anything I will do my best to do so. Thank you!
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post #2 of 71 (permalink) Old Jul 31st, 19, 9:58 PM
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Rick
 
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Re: The LS swap A/C blues

Hello Neil,

You wrote "fan turning on/off". I presume you mean the electric fans behind the radiator? If yes, the compressor head pressure is going to go high when the fan(s) is off because no heat is being removed from the condenser.

What happens when driving down the road with the AC running? My guess is better performance because driving airflow is removing condenser heat.

No heat or AC yet for me but I will wire my 70 EC so that any time my AC is on both of my Cold Case radiator fans will also be running. I can easily do this because my E-fans are not controlled by my LS powertrain control module - the fans have a separate controller. This is the Four Seasons part number 35879 that has a blue wire for use by the air conditioning system to turn on fan power anytime AC is running.

Rick

1970 El Camino under Reconstruction - 5.3L LS VORTEC Engine and 4L60E Transmission
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post #3 of 71 (permalink) Old Jul 31st, 19, 11:21 PM
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Bob
 
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Re: The LS swap A/C blues

Here is what I know. I have a 70 with a 468 B.B. I converted my system to R-134. FIRST: R-134 has a different expansion rate than R-12. When the Comp. is engaged the P. Flow condenser NEEDS AIRFLOW.
If you can not COOL DOWN the R-134 with the cond. you will have issues.
This is what I have in my 70, Alum. 10 Cyl. R-134 compressor, From the Fla. Guys. Same parts as you have. POA, adjusted for 134---P. Flow Condenser built for a 70-72 (uses all org. nuts bolts & brackets) 134-dryer.
I also have the 4 row copper /brass rad. ( Standard cooling system for a 70-72 with A/C. My fan blade is a 3947772 on a clutch. My engine temp never goes over 185 / 190. NOTE: VERY IMPORTANT--- A factory C-60 system takes a R-12 Charge of " 60 OZs " When you convert to the R-134 system with all the correct parts. The R-134 has a VERY DIFFERENT EXPENSION RATE than R-12.
Using the R-12--60 Oz. when you convert you use the 80% RULE, What the HELL is the 80% RULE????
80% of the 60oz = 48 OZs. Put it in simple terms. Charge your system with " 48 " OZs of R-134......... YES,,, Charge your system with 48 OZs AKA 3 LBS. of 134...... Dont even look at the gauges, Just shoot it up with 48 OZs of R-134..
I just tested my converted system yesterday, I am getting 38 to 40 degrees out of the center vent in my 1970 FRAUD SS 468 Nomad Sta. Wgn.
Bottom line when the Comp. clutch kicks in,,, You need a " TON " of air going over the P. Flow Condenser.
I am leaving for the OHIO Chevelle show at 8:00 AM in the Morn.
REMEMBER- 48 OZs of R-134 NO more NO less for a 60 OZ. G.M. system .
80% of the factory R-12. Due to the fact, R-134 has a VERY different expansion rate, OR it runs a lot hotter than the R-12. Suck it out and SHOOT it up with 48 OZs of R-134. Remember LOTTSA AIR over the Cond.
Bob
The above information is for 69-72 Chevelles. I also have a 70 El Camino SS 454 /M-22 that I ordered in Feb. of 70. I will get back to you on Monday!
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1970 SS LS-5/M-22 El Camino- Org. Owner-AACA 2016-Senior Grand National Winner---MCACN-GOLD-2013
1970 ( FRAUD) SS 468 Station Wagon - Driver.
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post #4 of 71 (permalink) Old Aug 1st, 19, 4:08 AM
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Re: The LS swap A/C blues

Did you install a new reciever/drier and vac the system down before charging? If you did not do this, then stop now and start over.
Did you add oil to the compressor and drier before recharging?
What was your POA valve pressure set at?
On a 72, there's a temp switch mounted to the outside of the a/c suit case that disengages the clutch. Has this been incorporated into your clutch control circuit?
Why are you using a TCS switch?


Your system is not a cycling system. That high pressure switch is there to cut power to the compressor only if high pressures are detected. 400 PSI IS WAY OVER THE LIMIT for safe operation on 134a at just about any ambient temp we're bound to experience. Your high pressures are all over the place because you did not cool the evaporator and run up the rpm to 1500 rpm. Another reason for high pressures is a blockage in the system.

The compressor should keep running 100% of the time that the a/c is on. There's also a low pressure switch that does just the opposite, when there is low pressure it shuts down the system to protect it from running when pressures are too low. The thermal switch cuts power to the compressor to control evaporator freeze up.

Your entire issue maybe that your fans are not on when the compressor is on. Lack of cooling of the condenser will send your high side pressures sky high and result in no cooling. You also over charged the system because your rpms should have been 1500 rpm while charging and you should only charge your high side according to the corresponding mid point of the pressure chart. Use the pressures on the chart according to the measured ambient temp.

You need to start with a good ambient temp reading. Wire up your cooling fans to turn on anytime the compressor kicks in. Later you can modify your fans to come on anytime your high pressure is over 180 psi to 225 and stay on at psi over that. Put a large fan in front of the radiator. Charge or recover refrigerant until you are in the mid range of the pressure range of the pressure chart for the corresponding ambient temp. Disregard your low pressure and charge per the high pressure reading.

After that's done, what is the ambient temp, high and low pressures, and temp out of the center vent? Are you pressures stable? If it's not cool and stable we have other issues. The gauges will tell the story.

The expansion valve and POA valve are what determine your low pressures. Your POA valve should have been set at 26 psi. A POA Valve prevents the evaporator from freezing by by-passing excessive system pressure. It's what allows the clutch to remain on all the time the a/c is running.
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post #5 of 71 (permalink) Old Aug 1st, 19, 12:24 PM Thread Starter
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neil
 
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Re: The LS swap A/C blues

Here are some pictures of what I'm working with. As you can see the system has been changed to work with the ls motor. Is it possible the POA is not functioning properly?

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post #6 of 71 (permalink) Old Aug 1st, 19, 12:29 PM Thread Starter
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neil
 
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Re: The LS swap A/C blues

Yes it has a new reciever drier. Tonight I'm going to try bypassing the thermal cycling switch and run the fans/compressor strictly off the trinary switch and see what this does.

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post #7 of 71 (permalink) Old Aug 1st, 19, 1:18 PM
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Re: The LS swap A/C blues

That's not a POA valve. That's a POA valve eliminator. Your system is now a clutch cycling system controlled by the clutch and switches. Technically, you don't have a POA valve and there is nothing in the POA valve eliminator valve that can malfunction.

Compressor cycling is controlled by the switch on the POA valve eliminator. If there is a high pressure switch in the system, and there should be, it's only function is to protect the compressor from high pressure. It's not actually used for cycling.

Set a fan in front of the condenser, engine at 1500 RPM, electric fans on, check your pressures. You may still be over charged. Use the line that corresponds to the ambient temp on the pressure chart. Get your high pressure in check first. My current guess is that the a/c shop set your high pressures in line with the ambient temps, but did not adjust the cycling valve on the low pressure side.

Then adjust the clutch cycling switch on the low side to 26 psi. Check your temps and pressures again and the temp at the output vent. Classic Air says to set for 21 psi, You might have to play with this and turn it down towards 21psi, The lower you go the cooler the temp, but you risk freezing up the evaporator. would stop lowering the psi at about 40degrees outlet temp,. If you hook up the thermo switch in the a/c suit case, you'll be able to run a lower psi because it will prevent freeze ups by also cycling the compressor. It should be run through a relay so the thermo switch doesn't take all the amps at it's contacts.

If your heater hoses are hooked up, use a valve or hose clamp plies to close the flow to the heater box.

Read the PDF, you can follow the instructions in it.

When you get your pressures and temps post them up.

Last picture is the a/c thermal switch mounted in the a/c suit case. Monitors temps in the evaporator box to prevent freeze up. There's another in the same area, thats the blower motor resistor. You can see the bmr in the upper right of this picture. These are located in the engine compartment.
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File Type: pdf POA Eliminator Kit 15-402 15-403 (1).pdf (1.06 MB, 10 views)
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post #8 of 71 (permalink) Old Aug 1st, 19, 1:28 PM
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Re: The LS swap A/C blues

It wouldn't hurt to clean the bugs off the evap ........killer.
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post #9 of 71 (permalink) Old Aug 1st, 19, 4:11 PM Thread Starter
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neil
 
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Re: The LS swap A/C blues

I just took some readings. All were taken with the motor at 1500rpm. Ambient temp of 80f
High side: 210psi with fans on compressor on and box fan in front of the condenser. The chart says 175-210
Low side: compressor off at 25, on at 49. That is the range of pressure I observed.
The coldest air I saw was 54f. The cold air comes when the compressor is on and goes away quickly when it is off.
I jumped the cycling switch on the POA ELIMINATOR(thank you for the education!) the low pressure ranged from 17-22 @1500 and the high stayed at 240-245. cabin temp got down to 43f but I noticed frost forming on the evaporator tube so I stopped what I was doing.
I have my pressure switches wired as follows: 12v from the original AC relay to the cycling switch to the trinary switch( located on the rec/dryer as shown in the pic) to the compressor(relayed).


Hopefully this gives a little more information, I have a tough time understanding mechanical things by written words alone
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post #10 of 71 (permalink) Old Aug 1st, 19, 4:54 PM
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Re: The LS swap A/C blues

You're still over charged. You should be running both fans on full for this phase with your pusher box fan in place. Recover some refrigerant until you get your high pressure down to about 200 psi. If you come out lower that's fine. No lower than 185. We may bump this up slowly later to peak cooling performance. I like to work at it from the lower pressure and add as I Watch system performance. By running a lower pressure here, you'll have less cycling of the compressor and a more constant flow of cool air. This is one of the pressures you play with to get a happy system when you use the POA valve eliminator.

So we want to drop that high pressure down, then adjust your cycle valve on the POA valve eliminator to show a minimum of 24psi psi. (We'll try it there, It's between the 26 I usually use and the 21 Recommended by vintage air.) You'll turn the adjusting screw to the right a full turn, then connect the cycle valve and check your low side pressure. For now, we want the low pressure to stay at or above 24 psi. (with r134a, your evap would freeze at 28 psi, but we lower the pressure to account for the air movement through the evaporator. This is another pressure we adjust for maximum performance. Every system is a little different, so hard numbers are hard to advise)

It's not unusual to see frost on the evap tube, so don't let that scare you too much. If your outlet temp is above 38 degrees, your not freezing the evaporator.

We'll work on your electrical system, like you I need to think about what you have going on. We'll try to incorporate the temp sensor switch in the evap box to prevent freezing under certain conditions.
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post #11 of 71 (permalink) Old Aug 1st, 19, 7:14 PM Thread Starter
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neil
 
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Re: The LS swap A/C blues

Quote:
Originally Posted by DUTCH MAX HEADWORK View Post
You're still over charged. You should be running both fans on full for this phase with your pusher box fan in place. Recover some refrigerant until you get your high pressure down to about 200 psi. If you come out lower that's fine. No lower than 185. We may bump this up slowly later to peak cooling performance. I like to work at it from the lower pressure and add as I Watch system performance. By running a lower pressure here, you'll have less cycling of the compressor and a more constant flow of cool air. This is one of the pressures you play with to get a happy system when you use the POA valve eliminator.



So we want to drop that high pressure down, then adjust your cycle valve on the POA valve eliminator to show a minimum of 24psi psi. (We'll try it there, It's between the 26 I usually use and the 21 Recommended by vintage air.) You'll turn the adjusting screw to the right a full turn, then connect the cycle valve and check your low side pressure. For now, we want the low pressure to stay at or above 24 psi. (with r134a, your evap would freeze at 28 psi, but we lower the pressure to account for the air movement through the evaporator. This is another pressure we adjust for maximum performance. Every system is a little different, so hard numbers are hard to advise)



It's not unusual to see frost on the evap tube, so don't let that scare you too much. If your outlet temp is above 38 degrees, your not freezing the evaporator.



We'll work on your electrical system, like you I need to think about what you have going on. We'll try to incorporate the temp sensor switch in the evap box to prevent freezing under certain conditions.
So before I read your latest reply I dropped the cycling switch down to 22psi. This resulted in about a 15% improvement. Previously I had about 50/50 cold/warm mix when at cruising speed. After dropping the shut off pressure to 22psi from 25, this improved to 65/35 cold/warm cruising with a vent temp range of 45-60.
I evacuated the high side. The ambient temperature went up to 82 so I evacuated to 195psi. I now have a 40/60 while cruising and vent temp ranging from 50-70. It just seems the only way I get cold air constantly is if I overcharge the system

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post #12 of 71 (permalink) Old Aug 1st, 19, 8:10 PM
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Re: The LS swap A/C blues

Did you evacuate the system prior to charging. Too much oil, moisture, or air in the system will reduce cooling temps.

Take a look at your sight glass, are you seeing any streaking or bubbles with the a/c on?

Your system is showing signs of a faulty expansion valve. Your vent temps are no where near where they should be, But we can check a few other things.

A blockage might cause an issue, showing as high pressure on the high side. Run your hand or temp gun over the line from the compressor to the condenser, over the condenser to the expansion valve. Look for frosting or areas where the temp goes from high to low. If you find one, there's a blockage at that point.

You may have an air flow issue through the condenser. Electric fans not pulling enough air while standing still. You can spray water on your condenser then check pressures. IF low, add refrig back to your chart levels. Or, leave the gauges hooked up out the back of the hood, duct tape to window then go for a ride and get some pressures while cruising down the road. If your high side pressures are low when cruising your charge can be increased. Then you have to increase air flow to your condenser. But if they are bouncing to max pressure then you'll have to start over, replace the TXV valve. re- evacuate the system and I would install a new drier.
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post #13 of 71 (permalink) Old Aug 1st, 19, 8:58 PM
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Re: The LS swap A/C blues

^^^Don't miss the above post.^^^

When you shut the car and a/c off watch your gauges. How long does it take for the 2 gauges to equalize in pressure?

When they do equalize, what is the pressure reading??

I really need the answer to the next question. Was the system evacuated (a vacuum put on system to 29hg for at least 30 minutes) prior to charging???
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post #14 of 71 (permalink) Old Aug 1st, 19, 9:15 PM Thread Starter
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neil
 
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Re: The LS swap A/C blues

Dutch I just want to say thank you for helping me with this and getting back to me so quickly. Yes I pulled vacuum for at least 30 minutes and it held 29in for another 30 after before I charged it. I will go over the lines tomorrow and look for temperature changes. The AC system worked great before I did the ls swap. It is a new expansion valve but it has a different sensing bulb than what was on prior to. It had the curly pig tail style and now it has the long flat bulb. This would not be the first nor the last time I've had brand new parts be faulty. It's also very possible something is plugged up. Thank you again I will report back tomorrow

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post #15 of 71 (permalink) Old Aug 1st, 19, 10:02 PM
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Re: The LS swap A/C blues

Quote:
Originally Posted by fasst450 View Post
Dutch I just want to say thank you for helping me with this and getting back to me so quickly. Yes I pulled vacuum for at least 30 minutes and it held 29in for another 30 after before I charged it. I will go over the lines tomorrow and look for temperature changes. The AC system worked great before I did the ls swap. It is a new expansion valve but it has a different sensing bulb than what was on prior to. It had the curly pig tail style and now it has the long flat bulb. This would not be the first nor the last time I've had brand new parts be faulty. It's also very possible something is plugged up. Thank you again I will report back tomorrow

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I'll wrack my brain some more and see what I come up with. Like reading technical stuff, trying to put into words a technical topic is difficult. It's so much easier and faster to be there and do it in person.

Check the equalization in the morning or when you get a chance. Before you start the car note the ambient temp and gauge readings. Start the car let the pressures build. Then shut off the car and watch your gauges. They should equalize within a few minutes. You can actually watch the low pressure side rise and the high pressure side drop as the high pressure moves through the expansion valve to the low pressure side. If it doesn't equalize within a couple of minutes the expansion valve is not functioning correctly. If it's not moving you can take the bulb loose and hold it in your hand or hot water. If the pressure the drops, your expansion valve is bad and needs to be replaced. Sometimes this will free a stuck valve, but the fix is usually temporary. There's a screen in the front of the expansion valve that can become plugged. Check for this if you pull the expansion valve. Hopefully it's clean.
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