AC in 1970 Malibu not cold enough - Chevelle Tech

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post #1 of 10 (permalink) Old Jun 13th, 12, 3:19 PM Thread Starter
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Dave
 
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AC in 1970 Malibu not cold enough

Hiya,

Years ago I had to replace the POA valve in my 1970 Malibu. I got a replacement unit from Year One. I remember my mechanic explaining that the old style relied on pressure to move freon into the AC system while this new one was wired in electrically and relied on periodic electrical pulses to provide freon.

I can imagine that this is true because my AC seems to alternate between blowing cool air and blowing warm air.

Has anyone else experienced this problem? I'm thinking that I need to do one of two things.

1. Figure a way to adjust the frequency/amount of freon being released into the system.

2. Re-wire things so that the freon is always being provided and this pause/gap doesn't happen.

As it is right now, it blows cool air for a while, but once it stops, the pause is long enough to really make the interior of the car warm up. Especially on 100 degree days. It's actually a toss-up between having the window down and having hot yet circulating air or leaving the windows up and having periodically cool air.
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post #2 of 10 (permalink) Old Jun 13th, 12, 3:25 PM
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Re: AC in 1970 Malibu not cold enough

Quote:
Originally Posted by pomegranate View Post
Hiya,

I remember my mechanic explaining that the old style relied on pressure to move freon into the AC system while this new one was wired in electrically and relied on periodic electrical pulses to provide freon.
WTF?????

I think you need a new mechanic or you need to learn to do some things for yourself. Electrical pulses? Do you have any data / links / url about this electrical pulse POA valve that has been wired in? POA valves can be modified to run r134 versus R12 and there are some later style valve arrangements that are different than the systems on these cars as delivered new. That said ...electrical pulses periodically delivering more refrigerant to the system? I don't think so but I have been wrong before.

Perhaps the "pressure" the old style POA /Systems relied on which he mentions is pressure from the compressor? Was that removed when the new style POA was "wired in" ???

A/C works based on expansion and contraction of the refrigerant gas (R134 or R12). Different pressure is seen in different parts of the system because of the state the gas is in. The state the gas is in depends on where it is in its expansion / contraction cycle.

The amount of refrigerant in the system is CONSTANT assuming there are no leaks. Once an initial charge is done no refrigerant is "released" into the system periodically. The gas just goes round and round picking up heat and discharging heat just like water in a hot water heating system. The temp and pressure of the refrigerant cycles up and down as it takes on heat or discharges heat. Does your mechanic have any clue as to how these things work or didn't you understand what he said?

Your symptoms sound like the unit is freezing up at the evaporator giving cool or warm air then thawing out and delivering cold air again until it refreezes. This is usually caused by an improper charge or possibly by insufficient air flow thru the A/C system due to a fan motor malfunction. At least that is how the systems work with the "old style" non electrical pulse POA valves.

This new style POA that has been "wired in" is not something I can comment on. Electric pulses?????

Last edited by oman; Jun 13th, 12 at 3:59 PM.
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post #3 of 10 (permalink) Old Jun 13th, 12, 4:00 PM Thread Starter
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Re: AC in 1970 Malibu not cold enough

Trust me, my mechanic is top notch. One of the few folks I will let touch my Malibu. I am speaking from memory about a part which was replaced at least 10 years ago. Yes, the POA valve is wired in electrically.

I do not believe that my system is freezing, as this happens any time the AC is on, no matter how long it's been running.

I understand that the refrigerant in the system is always the same amount and yes of course I have a working compressor. I understood what he told me to be referring to the amount being allowed to circulate. But I'm no AC expert which is why I'm asking here.

Here's a few photos of my new "old air" unit. Perhaps I will have to call them to get an answer.

Dave
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post #4 of 10 (permalink) Old Jun 13th, 12, 4:15 PM
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Re: AC in 1970 Malibu not cold enough

That is some sort of aftermarket / retrofit POA and not a POA that was originally installed on these cars. It might work the same way as the stock one but it is not an original unit. It likely is some sort of conversion unit...are you running R134? Were other mods done to the system when that thing was wired in?

Those wires go somewhere and depending on what they do there might be an issue with cool / cold / warm outlet duct temps. Is there ever water on the floor of the car after it starts producing warm or only "cool" air? Those wires connect to some sort of sensing switch set up that likely somehow regulates the flow of "Freon" thru the evaporator core based on pressure inside the closed loop system. It doess not IMHO add Freon to the system. It likely regulates the flow of freon but it is not adding freon.

You need to talk to someone who is running whatever kind of POA rig that is. Experience with how that system works as it is now configured is needed here. From what I can see that system has been modified ...unless of course the "POA" device you have in there just looks different than a stock one. Given the sensors and the wires it must be some sort of aftermarket mod to the system.
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post #5 of 10 (permalink) Old Jun 13th, 12, 4:19 PM Thread Starter
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Re: AC in 1970 Malibu not cold enough

Yes, it is an aftermarket mod. As I said, I got it from Year One and it is made by "Old Air Products." I couldn't find a POA valve in my parts store at the time so I ordered one from Year One.

Again, I understand it does not add freon as this is a closed system. I must have worded things improperly. I believe the original unit relied on negative pressure to bleed/pull freon through the system. The way I understand this one is that it relies on an electrical valve of some kind which periodically opens to permit freon to circulate. I may be wrong on this. It seems to me, however, that it's not allowing freon to circulate often enough so I get intermittent cold then warm airflow. I need more cold air flow.

There's no water anywhere in my vehicle. Well, except when it rains as I have to redo the firewall body seals! But that started happening long after I had this "new" POA valve put into place. I'll trace down the wires later to see where they lead.

I also emailed Old Air Products to get their opinion.

Dave
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post #6 of 10 (permalink) Old Jun 13th, 12, 4:27 PM
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Re: AC in 1970 Malibu not cold enough

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Originally Posted by pomegranate View Post
Yes, it is an aftermarket mod. As I said, I got it from Year One and it is made by "Old Air Products." I couldn't find a POA valve in my parts store at the time so I ordered one from Year One.

Again, I understand it does not add freon as this is a closed system. I must have worded things improperly. I believe the original unit relied on negative pressure to bleed/pull freon through the system. The way I understand this one is that it relies on an electrical valve of some kind which periodically opens to permit freon to circulate. I may be wrong on this. It seems to me, however, that it's not allowing freon to circulate often enough so I get intermittent cold then warm airflow. I need more cold air flow.

There's no water anywhere in my vehicle. Well, except when it rains as I have to redo the firewall body seals! But that started happening long after I had this "new" POA valve put into place. I'll trace down the wires later to see where they lead.

I also emailed Old Air Products to get their opinion.

Dave
"The way I understand this one is that it relies on an electrical valve of some kind which periodically opens to permit freon to circulate." That might be what is going: on said that way it makes more sense. If it regulates the flow of Freon and it is not working right then the system could be starving for Freon. No Freon in the evap = no heat transfer of heat from the cabin.

Your initial post said you got the valve from Year One..no mention of Old Air as the source. Had I known that it was an Old Air aftermarket / modification piece my response would have been different. Old Air or an Old Air user is your path to an answer on this!
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post #7 of 10 (permalink) Old Jun 13th, 12, 4:58 PM Thread Starter
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Re: AC in 1970 Malibu not cold enough

I do appreciate you taking the time to respond.
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post #8 of 10 (permalink) Old Jun 13th, 12, 8:57 PM
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Re: AC in 1970 Malibu not cold enough

I must say, Call Classic Air in Tampa Fla. and get you A/C unit back to the stock form. It was not designed to cycle! You can buy P.O.A. valves.
Any one that removes a POA valve from a 70 G.M. A/C unit, And replaces it with something else, Should NOT be permitted to work on the best Factory A/C unit ever built.
A good wrench turner would never go that route. My one owner LS-5/ M-22 car has R-12, My driver has R134 ( POA-Adj. for 134)and they are 100% G.M. org. Comming home Sunday from CB-2012 it was 92 degrees in Kentucky, My SS 454 Sta. Wgn. was so cold with 134, I had to roll the window down. You do not need a second opinion, You need someone that knows what they are doing!
Bob

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post #9 of 10 (permalink) Old Jun 13th, 12, 10:56 PM
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Re: AC in 1970 Malibu not cold enough

The setup in the pic is to convert the system to clutch cycling system like the newer cars. If you remove the wire plug and look in the end where the electricial plugs in you will see a small screw. It needs to be adjusted so the low pressure is around 24 lbs at which cuts the compressor off and also brings down the point at which the compressor cuts on making the air colder and the on cycle longer. As for the design, the 62-67 novas used the cycle system and they worked just fine, pumping out 40* air at the vents. I have converted 5 66-68 model GMs to the clutch cycle system and had no problems with them pumping out 44* air. With that said, I also think the Factory setup is best, but with 134A the old POA must be adjusted and you really need the new condensor for 134A to max it out.

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post #10 of 10 (permalink) Old Jun 14th, 12, 1:02 PM Thread Starter
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Re: AC in 1970 Malibu not cold enough

Quote:
Originally Posted by elcamino66 View Post
The setup in the pic is to convert the system to clutch cycling system like the newer cars. If you remove the wire plug and look in the end where the electricial plugs in you will see a small screw. It needs to be adjusted so the low pressure is around 24 lbs at which cuts the compressor off and also brings down the point at which the compressor cuts on making the air colder and the on cycle longer. As for the design, the 62-67 novas used the cycle system and they worked just fine, pumping out 40* air at the vents. I have converted 5 66-68 model GMs to the clutch cycle system and had no problems with them pumping out 44* air. With that said, I also think the Factory setup is best, but with 134A the old POA must be adjusted and you really need the new condensor for 134A to max it out.
Thank you for an informative and non-dogmatic response. I will take a look during my lunch break.
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