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1968 Impala ac rebuild

Cautrell05 on Tue May 19, 2009 12:20 PM User is offline

Year: 1668
Make: Chevy
Model: Impala
Engine Size: 350
Refrigerant Type: none yet
Ambient Temp: 80
Pressure Low: -
Pressure High: -
Country of Origin: United States

I have a 68 Impala that I am rebuilding right now. New ramjet 350, acc brackets from a 91 impala, R4 compressor. New condensor, The old one had the lower fitting broken off of it 13 years ago or so. New dryer txp valve. I need to remove the heater box and replace the heater core and blower motor and was planning on cleaning and pressure checking the evaporator while its apart.

The big question is the poa valve. From looking around they are hard to come by and expensive for nos parts. What would it hurt to use one of these http://www.oldairproducts.com/catalog/product_info.php?cPath=400_405_4051968&products_id=3674 and the exp valve? I work in a GM dealership and really the only time I have seen compressors cycle is when its cold or they are low on charge. When operating properly they dont cycle. I know from searching on here the poa valve is probably a better system but they are hard to find replacements for and when the car is finished it is going to my mother and her husband. My 90 handa has a txv and blows 35 at the vents in 90 dergee days on r12, and my 89 gmc blows low 40s on a mixture when its full.

I have no problem keeping the expansion valve but would like to simplify things if it would make it more reliable. The old guys at the shop here said they remember replacing alot of them back in the day. Looking for options and opinions. Thanks
Nick

bohica2xo on Tue May 19, 2009 4:13 PM User is offline

You work at a GM dealership?

Toss the R4 in the trash can, and fit a V7. Then you still have evaporator pressure control, and a TXV. Stuff the biggest PF condensor in it that will fit - think late model Suburban. Use the big fan too.

Sell your old POA to someone doing a restoration, since you are buliding a DD.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Cautrell05 on Tue May 19, 2009 5:56 PM User is offline

Im kinda stuck with the R4 due to engine bracket choices. The brackets off of a vortec truck wont work due to heater hose routing and other plumbing issues. The 91-93 impala mounts are about my only option for brackets other than aftermarket. The old compressor mounts off of the exhaust manifold and the lt1 manifolds are way different than the center dumps.

So your saying the poa kit is ok right? I need to talk to my service manager but I think if I pay the shop the 1.5 at employee rate to install the compressor(of which I get paid) then its lifetime parts and labor. Need to find out for sure. What do you mean by PF condensor? Thanks

Also, how does the placement of the dryer affect system performance? I noticed tonight that the OE dryer is on the high side between the comp and the condenser. But on just about everything built recently that I have looked at its on the low side after the evaporator. Does it matter?
Thanks

Nick

Edited: Wed May 20, 2009 at 1:13 AM by Cautrell05

mk378 on Wed May 20, 2009 10:06 AM User is offline

On a TXV system the receiver is between the condenser and the TXV. On a CCOT, used on later model GM cars, the tank is called an accumulator and is between the evaporator and compressor. Completely different systems, and the tank is plumbed differently inside.

The TXV is generally considered a better system. A variable compressor would be ideal, but if you can't fit that, install an evaporator temperature switch. The switch cycles the compressor off when the evaporator gets too cold to prevent freeze-up. Most Japanese cars up until the mid '90s (when computer controls became common) will contain a suitable switch.

Do not use the so-called POA eliminator, trying to cycle a TXV system on pressure causes rapid cycling and early wearout of the compressor clutch. Set up the system like a modern TXV: plumb the evaporator directly to the compressor and cycle on temperature. You also need a so-called "trinary" switch on the high side to protect against abnormal over or under pressure.

Cautrell05 on Wed May 20, 2009 10:57 AM User is offline

Thanks for the info on the dryer/ accumulator. Never really thought about it and just didnt know.

I knew the txv was better than the ot system. didnt see much reason to change that.

"Set up the system like a modern TXV: plumb the evaporator directly to the compressor and cycle on temperature. "
You lost me there, ditch the poa or not? Plumbing the evap straight to the comp was what I had in mind.

Nick

Cautrell05 on Fri May 22, 2009 9:19 AM User is offline

Anybody else have any input here?

Thanks
Nick

badfish on Tue May 26, 2009 10:27 PM User is offlineView users profile

I cant believe I remembered how to log on, it's been awhile.

Cautrell05, you're not stuck with that R4. About four years ago I was restoring a 66 Cutlass, we put a 350 ramjet in it as well.
I took bohica2xo's advice and used the V7 compressor. The compressor was from a Saturn VUE and the txv was from the same vehicle.

I used GM drve kit https://store.gmperformanceparts.com/store/SelectProd.do?prodId=7490

This is probably the same bracketry you are using. With a little creativity and and some skill with a die grinder you can finesse that
V7 right in there. That set worked great, by far the best non-stock performance ever to leave our shop. We also insulated that car very well.
good luck

bohica2xo on Wed May 27, 2009 12:30 PM User is offline

Badfish:

Thanks for the update, glad it worked out for you.

It is sad that the OP has the entire GM parts catalog available (at a discount), and still wants to put a craptastic R4 in that car. The V7 is a great replacment for an A6/POA, since it has the same displacment as the A6 did & incorporates the POA function in the compressor. I hate to see someone give up 2 CID per rev on a big car.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Cautrell05 on Wed May 27, 2009 1:12 PM User is offline

I may have the whole gmpp book available but im still on a buget. What compressor are you refering to that will fit those brackets?
this seems to be the common one for the vues
http://www.acpartshouse.com/showitem.aspx?id=102208&name=Remanufactured%20SC100V%20A%2FC%20Compressor&
short of building it from scratch I dont see how that will mount in place of the r4.
The v5 seems similar but all the pics of the v7 that I have seen look like the ones on on the ls series motors.
Nick

bohica2xo on Wed May 27, 2009 3:10 PM User is offline

They make the V7 in both case styles:

4 ear V7 from 2000 S10

Pad Mount V7 from Corvette

As far as the budget goes, there should be enough dead GM vehicles around the average dealership to scrounge 90% of it. The parts catalog gets you the right numbers/models/years - and any things like new idlers can come from the parts counter. Around here Pic-A-Part is full of GM stuff, and the brackets are usually still there.

It sounds like Badfish modified an R4 bracket to take the 4 ear V7. A set of brackets from a Corvette, or 1998~2002 Camaro should work for a pad mount unit

The V5 & V7 share a lot of things, like mounting surfaces & clutches. Grab a core V5 and have a look at the R4 bracket to see if Badfish's mod will work for you. If you want a different clutch/pulley on the V7 you can use any V5 clutch assembly - even a v belt.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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