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Anybody got any pics of the original 70-74 AC setups underhood?
Mine has air, but the compressor is gone along with a couple hoses.

Also, anyone know what the compressor is? I think Delco.
What cars interchange? trying to keep this part of the car close to original, as it came with air.
I know I will have to do a 134A retrofit for sure.
 

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I have A/C on my Nova (with everything still there - - I'm redoing my a/c hoses now) .
But, I still have the GM (Chevy) style ' A-6 ' compressor ………… I'm thinking of switching to this :


That way it will still fit & bolt up too my a/c brackets .
OR
Here is the ' Rebuilt A6 type A/C compressor ' ;


OR - - - even better , " CVF racing Sanden style A/C compressor = with "Life Time Warranty" .


but, then . . . I would need a new a/c comp. mount bracket .

just some different ideas ……………….. later , jim
 

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The original compressor is a Frigidaire A6. They are enormous and heavy, but also known to be relatively bullet proof. Many folks swap them out for a newer Sanden compressor which will also work.

I'm going to copy-paste some useful information below regarding how to get the factory system working well, since I have gone through this on my '70. I'm happy to answer any questions you have. I'm a mechanical engineer who studies heat transfer / heat pump / AC systems and this factory AC system design and operation fascinates me quite a bit. The system and it's operation are fairly simple, but there are some pitfalls even if the components are in good working order.

There are a few important thing to consider when using the factory AC and 134a
(1) The expansion valve (TX valve) needs to be appropriate for 134a due to different superheat temperature needs. Most replacement TX valves are already setup for 134a, but if you have an original TX valve you should replace it. When using an R12 TXV with R134a, the evaporator will not be fully utilized because the refrigerant will be superheated more than necessary. The result is less cooling capacity, leading to higher temperatures out of the vent.
(2) The POA valve needs to be adjusted so the pressure in the evaporator is correct to keep r134a near freezing. The original pressure setpoint (29psi) keeps R12 just above freezing, but 134a at the same pressure will be at a higher temperature. This means if you don't adjust the POA valve, your evaporator will be warmer and therefore the air coming out of your vents will be warmer too. The pressure needs to be lowered to abot 25psia. I have a video of doing that here:
(3) The condenser should be replaced with a parallel flow condenser. The original condenser is a tube and fin design which is much less efficient at heat transfer and it becomes a major limiting factor, especially when using r134a. Get the largest parallel flow condenser that you can fit and get good air flow. If you use the original condenser, pressures will rise on the high side of the system and it may not be able to keep up with cooling demand in high ambient temperatures, again leading to higher vent temperatures.

Other things you can do to maximize performance:
(1) Make sure the high speed fan relay is working properly. This relay is located on top of the AC box and it is only turned on when the fan switch is set to high speed. If it doesn't work, your blower motor will not have the maximum speed.
(2) Make sure your fan is getting a good dedicated ground. The fan motor mounts to a fiberglass, non conducting box on the firewall, so it needs a dedicated ground wire to the body of the fan. You can run this down to the frame if you want to ensure best ground.
(3) Ensure all duct work is sealed. You can use household self-adhering weatherstripping foam to replace the original seals if they are not working. Air blowing around under the dash is not as effective as air blowing at the passengers.
(4) Use an electric radiator fan with a shroud. Getting good air flow through the condenser is critical, especially if you want good performance when the car is sitting still.
(5) Make sure re circulation function is working. When set to "Max", the factory AC has a vacuum valve that operates a re circulation flap in the passenger footwell area as well as one on top of the cowl. If it's working propertly, you will hear more fan noise from the passenger footwell area when the AC is set to "max". If it's not working properly, make sure the vacuum lines are connected to manifold vacuum and that the duct operators are working.
(6) Make sure the heater shutoff valve is working. There should be a vacuum-operated shutoff valve located on the inner fender that stops the flow of coolant to the heater core when the AC is set to max.

Here are some photos of my factory AC setup as originally configured when I picked up the car in 1998. This is a 1970 with a 350 2bbl engine. Sorry these photos aren't the best because I took them with a film camera and scanned them roughly 20 years ago. You can see the original A6 compressor mounted on the driver's side. The low side hose routes over the engine and connects to the output of the POA valve while the high side hose routes forward through the radiator support to connect to the condensor. The compressor and associated bracketry were very heavy.









Here is what my system looks like today. I have converted to an LS engine and I'm using a Denso compressor that came on mid/late 2000s Silverados which is low mounted on the passenger side. I notched my subframe so it would fit there, otherwise there isn't normally room. The firewall unit is original to the car; I flushed the evaporator and POA valve, tested and readjusted the setpoint as described above, replaced the TXV, and hooked everything up with new hoses to a new drier and a new, parallel flow condenser. The system is working well except my vacuum control valve is finicky and sometimes re-circulation doesn't work.





 

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Clint ……… Thank you very much , great info .

I'm installing all new "barrier a/c hose" , and have a shop that will restore my hoses (using my
original metal sections of my a/c lines) . Then , I DO Have a new Dryer , new Expansion valve ,
new Heater control valve . And, a New POA valve Conversion kit . Then, I have been reading
up about the " Parallel Flow Condenser " …...
thinking that would be a good up-grade (over the 'tube & fin' stock unit). I would like too use my
stock 'condenser' - - - but , only want too do this once - - - can that be used ?
My unit Still Uses the stock A6 comp. - - - but, I 'd like too use the "Sanden Type Compressor"
BECAUSE of the 'A6' "draw on the engine" ……….. 69 Nova 250 / I-6 with Factory A/C (not
dealer add -on) - still complete . I Did charge with R-12 (back many years ago) ………… BUT ,
still had the 'rubber a/c hose' ; and leaked through the hose.

Lately, I have had the wild idea of = = = Could I adapt a New Sanden (508) Type compressor
onto my stock ( A6 ) engine mount ? ? May be a 'chore' ; over just buying the Chevy
Six aftermarket a/c mount - - - ? ? ? - - -
( meaning ……. who would ever think a 1993 T 5 tranny would bolt
into a 69 Nova ; 6 cylinder and, work so well ) . (just thinking that I could adapt
the newer Sanden comp too my A6 engine mounts ) .

Thanks again for the above info . (ps . I can use any help you may have ) , jim
 

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I'll do my best on the three topics you mentioned.

First, the POA conversion.

To understand the POA conversion, let me first explain how the original systems works. On the original system when the AC is on, the compressor runs continuously any time you set the leftmost control lever on Max AC or below or when defrost is selected. The clutch is activated the moment you move the control lever and the compressor continues to be driven by the engine the entire time the AC is on ("non-cycling"). The compressor "sucks" from the evaporator pulling the pressure down and thereby reducing the boiling point of the freon to a very low temperature. Without some kind of control, the compressor will suck the evaporator pressure down so the boiling point of the freon is well below the freezing point of water. That makes the evaporator temperature very low. If that happens, air going through the evaporator into the cabin of the car will get so cold that water will condensate out of it and freeze. Over time so much water will freeze that the evaporator will "ice up", becoming blocked so badly that air can no longer flow through it, stopping AC function in its tracks. The result is you would have an ice maker instead of an air conditioner!

The way engineers resolved this on the original system was to install the POA (pilot operated absolute) valve. The POA is basically a pressure regulator. The compressor is allowed to suck the evaporator down until it reaches a set pressure point, then the POA valve begins to close off, preventing the compressor from sucking the pressure down any further. The POA will then maintain a constant absolute pressure inside of the evaporator. This keeps freon boiling at a temperature near freezing, but not so cold that ice forms on the evaporator. As I mentioned above, if that pressure setpoint isn't adjusted for R134a the system will not operate well because R134a has a different boiling point from R12. This is a pretty slick way of allowing the system to reach a happy operating point that maximizes cooling in the cabin. The only reason to consider a different operation for this system is if the POA valve is acting up or defective. If the valve gets sticky or fails, the evaporator can end up operating at too high of a pressure which raises in the temperature or too low of a pressure which causes the evaporator to ice over.

Now let's discuss the "POA conversion" aka "POA eliminator". Somewhere along the lines the powers that be stopped manufacturing replacement POA valves. POA valves were not originally designed for rebuild, so the aftermarket stepped in with a very simple pressure-switch based "POA conversion" that replaces the entire POA valve with a simple, very inexpensive tube and a pressure switch. Instead of a mechanical valve to regulate the pressure in the evaporator, the "POA conversion" uses the set point of the pressure switch to turn off the compressor clutch when the pressure gets too low in the evaporator.The operation goes something like this: the compressor begins sucking down the evaporator to a low pressure, freon boils in the evaporator, as the pressure gets low the boiling point of the freon approaches freezing, then the pressure switch turns off the compressor so it never gets so low that the evaporator freezes. Then as the pressure begins to rise again,the pressure switch turns the compressor back on and the cycle repeats over and over.This is referred to a "cycling" or "clutch cycling" operation. There is window between the "turn off" and "turn on" setpoints of the pressure switch where the compressor stops running to prevent the evaporator from icing over. During this window, the temperature of the evaporator goes through a swing which on average will be a little higher than the steady temperature a POA valve can maintain. Also due to the swing in pressure/temperate, the TXV valve also goes through a bit of an operating swing. For these reasons, the cooling performance is not quite as good with a "POA conversion", but the operation is simplified and at least the operation of the "POA conversion" is very reliable. There is however one other important consideration for the "POA conversion" - the cycling of the clutch. The clutches on A6 compressors were not designed with cycling in mind, so they are not particularly suited for this type of operation. Also, every time the system cycles, your engine will have to adjust to bump the idle back up, and this cycling can lead to engine stalls and inconsistent operation.

Based on my research into this subject, I felt keeping the original POA valve operation and adjusting it for R134a would lead to better performance and so far I have not been disappointed. If you decide to keep the original POA operation and you do not want to get the tools to test or adjust the valve, you can send it off to a few places that will adjust it for you or cut it open and rebuild if it is defective.

Next the compressor

For operational purposes, the two important factors for a compressor are the displacement and efficiency. The displacement needs to be enough to develop pressure in the condenser in order to reject heat. The way the AC works is that the boiled-off freon coming out of the evaporator has to be compressed so the temperature rises high enough to reject heat to the air out in front of the car through the condenser. The hotter it is outside, the higher the pressure required to get the temperature up to reject heat. If you can't compress the freon fast enough to get the pressure up, you will not be able to reject as much heat and ultimately the system will not cool your cabin as well. The A6 compressor is a fairly high displacement compressor at about 207cc per rev and it's sized that large because these cars came with a very high capacity evaporator. By comparison, the Sanden SD709 displaces 155cc, about 25% less. Ultimately the displacement affects the overall capacity of the system, assuming the pulley ratios are similar. There is a good article on the A6 here discussing it's capacity: Frigidaire A-6 Air-Conditioning Compressor I have honestly never gone into the details of calculating all the system component operations to really understand how much compressor capacity is needed under different conditions for this system. On my system I am using a Deso 10S17 which has a displacement of 177cc/rev. It seems to be working fine and keeps up with demand when I'm driving at around 100deg F ambient. Lots of people have swapped over to Sanden compressors on these systems, so you can probably get a good idea from them on how well the Sanden compressor works. The other factor I mentioned, efficiency, is related to your concern that the compressor will put too much load on your I6 engine. Compressors with higher efficiency will be able to do the same amount of work on the freon with less work from the engine. I do not know exactly how the Sanden compressors compare with the A6. They are both piston type compressors but the Sanden has a shorter stroke and lower volume, which should result in an efficiency improvement. To some degree the load on the engine is more closely related to the amount of cooling demanded, which is a function of how hot the air is and how much air you're blowing around in the cabin. Personally I would just make sure you have a compressor that is in good working condition; either should do the job.

Now the pièce de résistance - the condenser

This is where you can get a huge bang for buck. In the 1960s and 70s, manufacturing technologies dictated the use of a "round tube and fin" condenser. This consists of a relatively large diameter piece of round tubing that is woven like a snake inside of a rectangular space and connected by fins that are intended to take heat away as air blows through. This type of condenser is limited by two factors: first the long length of relatively small tubing results in a pressure drop which requires a little more work from the compressor; in this way it's a "serial flow", since all freon has to travel the entire length of this goofy snake of tubing, building pressure along the way. Second, the amount of area available for air to cool the freon is limited by the size of the tubing and the area of the "fins".Heat can only be transferred from the freon through a relatively small conduction route between the tube and the fin (it's basically a line contact around the tube) and the tube itself has a relatively small surface area in contact with the freon or air. Because of these limitations, round tube & fin condensers are limited in performance. It was less of a problem with R12 freon, but becomes a limiting factor for R134a.

Modern condensers are "flat tube" "parallel flow". What this means is there are two end "tanks" for the inlet and outlet with flat shaped tubes that connect them. This has two advantages: first, the flow of freon coming into the end tanks is divided so that freon splits up and flows into all the paralell paths of the tubes. The parallel paths are much much shorter than what would be required to snake through all the paths in series, so the pressure required to move the freon is a lot less. Secondly, and very importantly, the shape of the tube themselves is very flat.This increases the surface area substantially, which allows more heat to be rejected more easily from the condenser. That allows the compressor to run at low pressures, reducing the load on the engine, and also ensures it can keep up with demand in higher ambient temperatures.

For all those reasons, you should absolutely throw the original condenser into the garbage and replace it with the largest parallel flow condenser you can find. It will both increase the overall performance of the system and reduce the load on the compressor.
 

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Clint ,

All 3 topics ……….. 10 - 4 . That's some really Good "Plain & Simple" answers . Even I can 'understand' ………..
Thank You For Your time & thoughts for each Topic . Over on the Pontiac "PY forms" . . . . a lot of guys
talk of 'restoring their original A/C systems ………… then, most all recommend going " Parallel Flow
w/ 134" . I was "leaning that way" = now I know .
Back when - - - - - I had my system charged w/ R12 …… everything worked good ; A6 comp, POA , TX
valve , .……(all stock stuff) …….. but, it had that old "rubber hoses on the system then, and it would just "percolate" out those hoses . Then, I don't 'hate th' A6 ; other than "the boat anchor part & it's Big " .
Thus my 'Sanden compressor thinking' , being newer (not 1969 year vintage) .

thanks again , jim
 

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Clint, great write up on the operation of old vs new AC systems.
When I had my '69 Nova w/250 cu in 6 engine, I added a new AC system from Classic Auto Air.
The Sanden compressor took very little power from my stock engine (Approx 200rpm) and cooled the interior nicely.

Jim........
 

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Thanks both. Good to hear about your results Jim! I forget you are both probably carbureted, so you be sure the idle-up solenoid is also setup. Basically when the AC is on, there should be power to a solenoid that moves the idle position up a little to compensate for extra load. That'll keep the engine from stalling and also keep the fan speed up so the system performs.
 

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Thanks both. Good to hear about your results Jim! I forget you are both probably carbureted, so you be sure the idle-up solenoid is also setup. Basically when the AC is on, there should be power to a solenoid that moves the idle position up a little to compensate for extra load. That'll keep the engine from stalling and also keep the fan speed up so the system performs.
Clint, my Nova never had a idle solenoid. I was able to get the idle just right for both air on and off, and not get engine after run when I turned the engine off.
I was also running an electronic distributor from Stovebolt 6. That distributor set up called for 10 to 12 degree advanced timing. Overall a nice set up.

Jim........
 

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Clint, my Nova never had a idle solenoid. I was able to get the idle just right for both air on and off, and not get engine after run when I turned the engine off.
I was also running an electronic distributor from Stovebolt 6. That distributor set up called for 10 to 12 degree advanced timing. Overall a nice set up.

Jim........
Ditto …. here .
At one time I did have the 'stock a/c idle solenoid' - - when my car had the stock Rochester mono-jet
1bbl carb . (solenoid & mounting bracket & wiring ; back in '97) . . . but, now using a Holley 390 - 4bbl
carb . I think I still have the sol & bracket . . somewhere . . but may not work with the Holley 390 .
I have thought about that - did the V 8 cars have that solenoid ?

just info . . . . . .

jim
 

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My 350 2bbl had the idle up solenoid, yes. Now I have an LS engine so the computer compensates for the compressor load.

They do make solenoids and brackets for all kinds of carburetor setups, so you might look into what's available. I would contact Holley and see what they offer.

EDIT If the 390 is a 4160 style carb, then Holley says to use Holley P/N 46-74 and bracket P/N 20-9

 

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Clint . . . . . . I was going too go look - today .

You're the " MAN " ...…...…….. Thank you . . . . (y)

ps = Holley # 8007 - 390 CFM 4bbl carb is - 4160 style carb .

Thanks again , jim
 

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Hey ….……. Corbinstein ………..

I did not want too "Hi-jack" anyone's post ; wasn't my meaning , for sure , & I'm sorry .

Then, You wanted a Picture of a stock GM A/C type A-6 a/c compressor :
stock GM a/c compressor - - but mounted on a stock 250 I-6 engine . Should be the same comp.
as found on the V-8 Novas & many other GM cars . Difference may be "amount of Freon charge …….. mounting brackets & hoses .
as in bigger cars , may take more Freon " .

# 1 - - mounted on factory Chevy Six engine : all compressor mounts & pulleys are "Chevy 6 only" .
with "VO1 - HD cooling" = V8 radiator (3 row) , 7 blade (V8) fan blade (3947772) , with Thermo Fan-Clutch …
(that I have been looking for , 21 years) , and, A/C six engine "Short Water Pump" (a/c only . . . which
makes the w/p pulley a/c only) . And , no fan shroud . But, does have the A/C lower close-out
" Baffle " , under the front bumper.



# 2 - - some V 8 motors did mount the A/C compressor on the 'drivers side of the engine - -
with the Alt , mounted on the top pass. side.



# 3 - -




ALL these will show up in the "Factory Assembly Manual" - - section C-60 , for your year Nova.
also, shows all V8 a/c mounts & brackets with 'stock part numbers ' .

The A 6 compressors are "rebuildable" (over the counter OR by you) .

Hope this may also help ………….. jim
 

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Jim do you have any photos of the close out panel under the bumper? I remember my car had one but it was lost or thrown out when I was rebuilding the front of my car 20 years ago. I think it may have been split or partially broken otherwise I probably would have saved it.
 

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Why - - - - - Yes - - - - - I do . as I understand , came on A/C cars only (even tho my 69 has factory A/C .. . . for just a six cylinder car .

Clint , here ya go .

# 1 - - two 'small tabs - broken - off (in the center area) . . . . two 'out-side tabs' are still there. The rear
edge areas on each side - have taken a hit, also.



# 2 - - you can see "the front Tabs" , a little better. It was on the car …………. it is still mounted on the car.



Also, there is a "rubber seal" going across the top (front edge) of the core support. That is too
seal any air that would come 'over the top' of your radiator .
NOTE : almost like the rubber seal at the back - by your 'cowl screen' .

Also seen here :


that seal Number (in my FAM is : 3940279 , page C 60 - B1) .

later, jim
 

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Thank you for the photos. That certainly looks familiar but I can't picture how it was mounted. I also had that rubber seal along the top of the core support - did not know it was being reproduced, so I'll be sure to pick some up.
 

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Clint ……….. I looked & could - not find the 'edit - button' anymore - - (on Flickr) too 'highlight
the mounting tabs'

# 3 - - another look :



so, look at the upper edge (front edge that 'screws to the front bumper' ; the two outsides tabs are
still intact . The two inner tabs are broken-off . . . . "very small tabs" . I'll try too take another pic - - under the car.
Then , look at the 'round hole' = that has a bolt that mounts onto the hood latch support (at the very bottom of the support ( I use a 'large flat washer there' ) .
At the bottom edge (back edge under the car) . . . . that area is the large broken spot on each side ;
I have a 1" x 4" metal (like a large washer , just not round ) ………. a short "flat - strap" that covers
those "broken areas on each side" .
For now , I cut & installed a 1" x 2" short flat - strap on each side of the front bumper . The front "tabs"
are supposed too hold the front edge up ; I don't trust those "tabs" ; so I bolted on the short 'flat-strap'
on each side . . . . then install the front edge on top of that flat-strap. That keeps the front edge from
dropping - down ………. which you don't want that too happen . If the front edge were too fall down ……...
going down the road - - - the "wind" would most likely rip - the - baffle - off.
Pictures are better . . . I'll get those.
I think a guy could make a new "baffle" - - - - I'd use 'metal' - - - - and, maybe make it in two 'parts' ;
then , pop-rivet it together .
just thinking out-loud ……… jim
 

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OK - I , also have pictures of the "rubber a/c core - support seal" . . . . . . . .
I'll have too load them . . . . . . . . shows ; where & how long . . . . . .
Both of those 'items' (lower baffle & top rubber seal) just makes more air-flow go through the radiator ;
instead of going 'around the radiator' . . . . . jim
 
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