Need help from the A/C pros.....LONG post.
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
OK, don't make fun of my mad photochop skills. 
Here's a picture that shows what I sealed. The system takes in air from the area below the windshield when the flapper is closed, as in the picture. On my car, with AC, the blower sits in the AC box at the upper right side of the plenum. When the flapper is open it pulls air from the area below the windshield and also from in the car which gives you the circulate feature. Unfortunately, if the seal of the fender has cracked, the blower also pulls in heat from the engine compartment and from the exhaust. Picture the yellow line with gaps and you can imagine what is being pulled in. In any event I sealed all the areas shown in yellow and its seemd to work well for the past 3 years or so in keeping heat out of the cocpit. Don't forget to leave a small area open at the bottom in case moisture gets in.
Here's a picture that shows what I sealed. The system takes in air from the area below the windshield when the flapper is closed, as in the picture. On my car, with AC, the blower sits in the AC box at the upper right side of the plenum. When the flapper is open it pulls air from the area below the windshield and also from in the car which gives you the circulate feature. Unfortunately, if the seal of the fender has cracked, the blower also pulls in heat from the engine compartment and from the exhaust. Picture the yellow line with gaps and you can imagine what is being pulled in. In any event I sealed all the areas shown in yellow and its seemd to work well for the past 3 years or so in keeping heat out of the cocpit. Don't forget to leave a small area open at the bottom in case moisture gets in.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
THANKS VETTFIXR,
Now I have an idea about where to reseal. Now about this flapper that you say opens and lets air in from the cowl...where the hell is it? is it the thing that I wrote FLAP on in my edited pic? trying to get an idea of how it opens and circulates.
Man I bet its a biotch to change that vacuum hose going to the vacuum pot in the plenum.....
Now I have an idea about where to reseal. Now about this flapper that you say opens and lets air in from the cowl...where the hell is it? is it the thing that I wrote FLAP on in my edited pic? trying to get an idea of how it opens and circulates.
Man I bet its a biotch to change that vacuum hose going to the vacuum pot in the plenum.....
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
The large oval shaped flapper on the bottom is the one I'm talking about. This is controlled from the inside of the car by a vacuum motor which opens and closes it in relation to the type of AC selected i.e. Normal or Max. On the Max air setting this flap opens and allows cockpit air to be pulled in by the blower and recirculated into the AC system. This allows the system to get colder faster. When you select Norm AC all air is pulled in from the outside which is less efficient because on a 90 degree day the system is always trying to cool 90 degree heat rather than 70 degree air from inside the cockpit. To get into this area you remove the door sill plate and the kick panel. You will then see the vacuum motor under the passenger side dash. If you want you can remove the passenger lower dash panel which makes all of this much easier. The vacuum motor is held by two bolts. Remove them and then remove the flapper completely. I forget exactly how its attached but it wasn't held on by much. You can then get your arm in there and apply the caulking. Just for giggles you should put a shop light under the car and then take an inspection mirror and look into the cavity. You will be amazed at how much light you see.
You can then get your arm in there and apply the caulking. Just for giggles you should put a shop light under the car and then take an inspection mirror and look into the cavity. You will be amazed at how much light you see.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
OK, I got it on the flapper.. I pretty much knew that stuff about THAT flapper but what about the other flap? the one that opens and closes off the air plenum? I need to know exactly where it is so I can check to see if its even working. It looks like in the pic that the upper flap is on the other side of the vacuum pot right there under the wiper door.
My oval flap works the way its supposed to on max and norm AC, it seems like it closes off pretty well when its closed. I will probably tear into this thing this saturday so I want to make sure I hit all the questionable areas for leakage
I really appreciate all your help. I am sure there are many others that are interested in fixing their AC themselves. Maybe we can make this a good tech thread and get it stickied if we have good results.
How cold does the AC blow in your car?
My oval flap works the way its supposed to on max and norm AC, it seems like it closes off pretty well when its closed. I will probably tear into this thing this saturday so I want to make sure I hit all the questionable areas for leakage
I really appreciate all your help. I am sure there are many others that are interested in fixing their AC themselves. Maybe we can make this a good tech thread and get it stickied if we have good results.
How cold does the AC blow in your car?
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
I don't remember offhand what the top vacuum motor does. In fact I'm not sure mine had that. If you look closely you'll see that the model shown is an early model with the vacuum door for the windshield wipers. Maybe it has something to do with that. I know on mine you can reach in through the flapper and put your hand on the blower wheel.
My AC is OK. I wouldn't say its outstanding but it does work. I've replaced the compressor twice and I've taken the whole system apart, cleaned it, and recharged it with R134. Like I said its OK. I think if I had to do it all over again I would have saved myself a lot of work and expense by just converting over to an aftermarket system.
What I don't like about our systems is:
1. The blower motors are weak even when working properly.
2. The ducts are large which causes a loss of airflow velocity
3. A6 compressors like to throw a lot of oil around in the engine compartment which I don't like given my engine compartment.
4.A6 compressors are horsepower hogs compared to modern units.
5. The system is bulky. Try to remove the AC/Heat box in the engine compartment and you'll see what I mean.
All in all it was a good system 30+ years ago but modern systems are much more efficient.
My AC is OK. I wouldn't say its outstanding but it does work. I've replaced the compressor twice and I've taken the whole system apart, cleaned it, and recharged it with R134. Like I said its OK. I think if I had to do it all over again I would have saved myself a lot of work and expense by just converting over to an aftermarket system.
What I don't like about our systems is:
1. The blower motors are weak even when working properly.
2. The ducts are large which causes a loss of airflow velocity
3. A6 compressors like to throw a lot of oil around in the engine compartment which I don't like given my engine compartment.
4.A6 compressors are horsepower hogs compared to modern units.
5. The system is bulky. Try to remove the AC/Heat box in the engine compartment and you'll see what I mean.
All in all it was a good system 30+ years ago but modern systems are much more efficient.
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
My 1970 service manual shows there to be TWO flaps. The oval in the kick and one above it. Thats what that vacuum pot you see there operates I believe..Maybe not...but... Anyway the upper flap is supposed to allow air in and out from the cowl area under the wipers and it works OPPOSITE of what the one in the kick panel is doing. one open/one closed and vice versa.
As for my AC, I am not expecting miracles nor am I gonna dump a bunch of money it but...90% of the time I have the tops off, rear window out etc. I want to keep my car as original as I can and I would like everything to work. I am not expecting a 40* ac but would like something usable in the even I get caught in the rain or I am on a long highway trip and don't want the wind noise etc.
On a side not, my original service manual states the discharge temp should be 46-49* on a vette. I am sure the system is "capable" of this assuming there is not hot air pouring into the system from everywhere.
I would contemplate going aftermarket AC if I didn't have to disrupt the firewall etc. I don't want it to not look stock but...I am sure thats the only way to eliminate the heating problem is to move it all inside the cab. Especially considering its only $1250 for the entire kit...not bad at all.
As for my AC, I am not expecting miracles nor am I gonna dump a bunch of money it but...90% of the time I have the tops off, rear window out etc. I want to keep my car as original as I can and I would like everything to work. I am not expecting a 40* ac but would like something usable in the even I get caught in the rain or I am on a long highway trip and don't want the wind noise etc.
On a side not, my original service manual states the discharge temp should be 46-49* on a vette. I am sure the system is "capable" of this assuming there is not hot air pouring into the system from everywhere.
I would contemplate going aftermarket AC if I didn't have to disrupt the firewall etc. I don't want it to not look stock but...I am sure thats the only way to eliminate the heating problem is to move it all inside the cab. Especially considering its only $1250 for the entire kit...not bad at all.
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
Jim, I was kind of thinking about fixing the heat problem before dumping freon in and checking for leaks. I figured if an old system blows 50*s at best, yet I am getting 100* in the system already...its not gonna be worth fixing.
Thats a good idea blocking both heater hoses. I just stuck a valve in one because I figured if I stopped the circulation, it wouldn't get hot. I will look into looping them.
As for my system, it appears to be the original compressor and POA valve, as well as the condenser but the hoses look to have been replaced as they still look relatively new but I know they are at least 18-19 yrs old.
If I turn the AC on, the compressor kicks on yet nothing gets cold, no pipes or anything. Something is wrong though because the compressor stays on all the time, even if I put the control on "Vent" or on "HTR" the compressor still stays locked in. All wiring and relays for the blower appears to be original although I did have to repair a few wires and add new insulated female slide connectors.
Once I realized the extreme heat leaking in to the system,I knew it would be pointless to go further.
I want to keep the factory ac and want it to be liveable at least. I know it can be done, one of my buddies down here has a 77 and his AC was converted to R134 but nothing else was changed and is completely original and his blows 50*.
Thats a good idea blocking both heater hoses. I just stuck a valve in one because I figured if I stopped the circulation, it wouldn't get hot. I will look into looping them.
As for my system, it appears to be the original compressor and POA valve, as well as the condenser but the hoses look to have been replaced as they still look relatively new but I know they are at least 18-19 yrs old.
If I turn the AC on, the compressor kicks on yet nothing gets cold, no pipes or anything. Something is wrong though because the compressor stays on all the time, even if I put the control on "Vent" or on "HTR" the compressor still stays locked in. All wiring and relays for the blower appears to be original although I did have to repair a few wires and add new insulated female slide connectors.
Once I realized the extreme heat leaking in to the system,I knew it would be pointless to go further.
I want to keep the factory ac and want it to be liveable at least. I know it can be done, one of my buddies down here has a 77 and his AC was converted to R134 but nothing else was changed and is completely original and his blows 50*.
Mine is an all original type system on R-134a, after having been open for years. Mine gets to 40 degrees on recirc, but I do need more airflow for it to be perfect. My outside door is sealed, with a shut-off in the supply heater hose.
These systems are horsepower hogs when it's pumping, but I REALLY like that it doesn't cycle all the time, and a 427 doesn't really notice the load
!One more thing. Make sure the compressor doesn't leak at the front seal, or make a guard over the top to prevent the light oil from collecting on the underside of the hood. The fiberglass is VERY porous and it'll ruin the hood (paint won't stick) if you let this go. Later vettes had a guard from the factory. You can guess how I know this...
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
The original POA valves are like gold, and rarely fail. On the compressor staying on all the time, there is a micro switch on the mode switch (the "wheel") that kicks it on and off at the approriate time and it must be stuck.
Mine is an all original type system on R-134a, after having been open for years. Mine gets to 40 degrees on recirc, but I do need more airflow for it to be perfect. My outside door is sealed, with a shut-off in the supply heater hose.
These systems are horsepower hogs when it's pumping, but I REALLY like that it doesn't cycle all the time, and a 427 doesn't really notice the load !
One more thing. Make sure the compressor doesn't leak at the front seal, or make a guard over the top to prevent the light oil from collecting on the underside of the hood. The fiberglass is VERY porous and it'll ruin the hood (paint won't stick) if you let this go. Later vettes had a guard from the factory. You can guess how I know this...
Mine is an all original type system on R-134a, after having been open for years. Mine gets to 40 degrees on recirc, but I do need more airflow for it to be perfect. My outside door is sealed, with a shut-off in the supply heater hose.
These systems are horsepower hogs when it's pumping, but I REALLY like that it doesn't cycle all the time, and a 427 doesn't really notice the load
!One more thing. Make sure the compressor doesn't leak at the front seal, or make a guard over the top to prevent the light oil from collecting on the underside of the hood. The fiberglass is VERY porous and it'll ruin the hood (paint won't stick) if you let this go. Later vettes had a guard from the factory. You can guess how I know this...
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Wrencher, ALSO how do you get to the outside door to seal it shut?
So right now, you are taking in NO outside air, only the cabin air right? so if you put your AC control on NORM, where does it get air from? or did you just remove the flap in the kick panel?
So right now, you are taking in NO outside air, only the cabin air right? so if you put your AC control on NORM, where does it get air from? or did you just remove the flap in the kick panel?
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Not sure I agree with this part, I've had two of them fail so far and the A/C guys all tell me they've historically been a problem. My experience with them is that they stick and do not let hot gas back into the system to keep the system from freezing. The result is your A/C will blow super good for a while then gradually start blowing warm humid air. The drain will also stop working because the system is iced up. When you shut it off the water will pour out as it unthaws.
Running the system in this condition builds up excessive pressures and is not good.
They're like gold for sure because you can't buy a new POA valve or a kit anymore to rebuild them, you have to buy the whole VIR unit and whether or not you get a good Chinese one these days is a crap shoot.
Running the system in this condition builds up excessive pressures and is not good.
They're like gold for sure because you can't buy a new POA valve or a kit anymore to rebuild them, you have to buy the whole VIR unit and whether or not you get a good Chinese one these days is a crap shoot.
Drifting
Joined: Mar 2004
Posts: 1,450
Likes: 40
From: Panama City Beach, Florida
Not sure I agree with this part, I've had two of them fail so far and the A/C guys all tell me they've historically been a problem. My experience with them is that they stick and do not let hot gas back into the system to keep the system from freezing. The result is your A/C will blow super good for a while then gradually start blowing warm humid air. The drain will also stop working because the system is iced up. When you shut it off the water will pour out as it unthaws.
Running the system in this condition builds up excessive pressures and is not good.
They're like gold for sure because you can't buy a new POA valve or a kit anymore to rebuild them, you have to buy the whole VIR unit and whether or not you get a good Chinese one these days is a crap shoot.
Running the system in this condition builds up excessive pressures and is not good.
They're like gold for sure because you can't buy a new POA valve or a kit anymore to rebuild them, you have to buy the whole VIR unit and whether or not you get a good Chinese one these days is a crap shoot.
Frank
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
I also heard the POA valves fail often. I thought you could get them though. I thought I remember seeing them in CC. I hope you can get them. I don't mind an aftermarket POA but I want to keep the rest of the system original if possible.
Good info guys.
Good info guys.
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
On the POA valves, I had less trouble with these than conventional expansion valve systems. Contamination will wreck anything, but for the most part I've had good luck with these when the system is clean. The part I like about them is it maintains optimum pressure to the expansion valve.
Last time I checked, the aftermarket POA valves (which look and fit like c**p) were no longer made and my vendors (NAPA, Hal's auto air) were out of stock. I got Hal's last one and still have it. I pick up the originals every chance I get and I have been lucky, I guess. I get them off of old sedans and trucks mostly when I need them.
Hans
Instructor
Joined: Mar 2006
Posts: 107
Likes: 0
good stuff
This is some good stuff. I have an 81 and messed with my AC system last year. I spent too much on R-12 and did not understand at all how the two flaps worked i just looked at them and was like "what the hell do i do with these??" So i ended up sealing the box in the engine, but now i will go back and seal that section as well. I think I may have the POA vavle issue... I live in Mi and its still cold so I dont drive the vett, but i think that it would work nice and cold....kinda..... and then get warmer. So if my POA is f'd what should I do? Also I for surly am getting hot air in my system because vent might as well be heat, Im hopeing that sealing that outter section will cut that out. This is a good thread with lots of good info. If some one knows if it sounds like my POA vavle is stuck some advice on what to do with it would be great. thanks guys
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
I didn't have time to mess with mine this past weekend. I am still looking for this "mystery door" that is the upper flap in the cowl. I still can not find it or see how it works. Wish I had a good pick of it. Gonna look at a CC catalog and see if anything shows it.
Either way my original blower motor is working great and hitting on all 4 speeds. I just gotta get the hot air problem solved before I start dumping freon in it. I MOST DEFINETLY am getting super heat coming in the system.
Either way my original blower motor is working great and hitting on all 4 speeds. I just gotta get the hot air problem solved before I start dumping freon in it. I MOST DEFINETLY am getting super heat coming in the system.
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
The POA valve is located in the VIR (link to picture)with another valve and some desicant material to absorb moisture.
http://www.ecklers.com/product.asp?p...dept%5Fid=1194
The VIR is located under the right front fender. You can get to the valves and remove/replace them in the VIR by first evacuating the Freon from the system and then removing the top of the VIR. There are several bolts around the top dome and an "O" ring that seals it up. When you put it back together make sure the "O" ring is seated properly. I bought a brand new VIR and the "O" ring was pinched, it leaked about $50 worth of Freon before I found it. Thank you China!
There are some other folks on here that are allot smarter than I am about this system, I think Wrencher could help you more. I'm just relating my experience with the damn thing. My POA is sticking now, I bought a used valve to take apart and see if I can make sure it's working properly before I go thru this for the third time
Good luck with yours
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
ajrothm, here's some photos of my A/C box showing the location of some of the doors with seals that are sometimes bad or not sealing. Remember mine is a 75 and might be a little different that yours. The one showing the heater box being removed from the car has a red circle around an arm for one of the doors. That is hooked to the temp slide on mine. Sometimes you can adjust the cable to make this door seal better and stop hot air from coming in.
Here's what that connected to:
This is a pic of the heater core showing the door that allows air to flow either thru the evaporator coil or the heater core
Here's what that connected to:
This is a pic of the heater core showing the door that allows air to flow either thru the evaporator coil or the heater core
Thread Starter
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Top Gunn, thanks for the pics, your ac box looks about like mine. I have checked my hot/cold door flap(the one thats cable operated) and it seems to close off and seal well. I also checked the other little door flap that moves when you put the defrost on and it changes the direction of the air flow.
The door that I can NOT find pics on is the plenum door in the cowl. Thats the one I want to check because I have never even seen it and it may or may not be working. Its in the cowl somewhere and has a vacuum pot running it opposite of what the door in the pass kick panel is doing.
If we do the closed cabin jobby...which door do we seal shut?
I would think that if you seal shut the door in the kick panel, wouldn't that block all the cabin air IN the cabin and not let it go into the plenum for the blower to pick up?
OR
Do we seal shut the plenum door, blocking out all outside air so therefore its FORCED to suck in only cabin air?
It would help if I could find the plenum door...LOL
The door that I can NOT find pics on is the plenum door in the cowl. Thats the one I want to check because I have never even seen it and it may or may not be working. Its in the cowl somewhere and has a vacuum pot running it opposite of what the door in the pass kick panel is doing.
If we do the closed cabin jobby...which door do we seal shut?
I would think that if you seal shut the door in the kick panel, wouldn't that block all the cabin air IN the cabin and not let it go into the plenum for the blower to pick up?
OR
Do we seal shut the plenum door, blocking out all outside air so therefore its FORCED to suck in only cabin air?
It would help if I could find the plenum door...LOL