A/C re-installed - how much oil / R134a to add and should I change the compressor?

[82DMC12]

A few years back I replaced EVERYTHING in my A/C system except for the evaporator so I could switch to R134a and it's been working pretty well. I bought a kit from Hervey but supplied my own custom parallel flow condenser.

Now, I recently had to open my A/C system in order to do a frame-off. I replaced the accumulator but re-used everything else except for the green o-rings that were exposed to the air when I had various fittings apart. I installed new o-rings and smeared them and the threads with Nylog Blue.

I am waiting on some parts and it looks like I could be 3-4 weeks out of commission before I can bring the car in to get the A/C recharged.

This week I'm going to get one of those compressed-air powered venturi pumps to draw a vacuum down and make sure I'm holding vacuum, plus that will get any moisture out of the system in case I'm stuck for longer than expected.

How much oil and how much R134a should I suggest the tech add when I do bring it in? Should I drain the compressor first or just leave it alone? it's a Sanden SD5 and I have a variable orifice valve .



Also - is the 8 piston Sanden going to have noticeably better performance than the SD5H14? I'm not trying to find stuff to spend money on but if it's a no-brainer to upgrade, now's the time to do it.

[DMC5180]

134a 1.9 -2.0 lbs

Sanden ships SD-5 and 7 series compressors with 135CC of PAG Oil. If your system is clean you can use PAG. If you still have components contaminated with Mineral Oil you should use Ester Oil.

There is no 8 cylinder compressor that I?m aware of. I used the SD-7H15 with QD head and Adapters to go with DPI hoses.
More Cylinders provides for a smoother quieter operation. It really helped reduce the Idle pull down from the OE SD-5. My system has been working flawlessly since doing the conversion in 2016. I haven?t had to touch it since.


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[82DMC12]

134a 1.9 -2.0 lbs

Sanden ships SD-5 and 7 series compressors with 135CC of PAG Oil. If your system is clean you can use PAG. If you still have components contaminated with Mineral Oil you should use Ester Oil.

There is no 8 cylinder compressor that I?m aware of. I used the SD-7H15 with QD head and Adapters to go with DPI hoses.
More Cylinders provides for a smoother quieter operation. It really helped reduce the Idle pull down from the OE SD-5. My system has been working flawlessly since doing the conversion in 2016. I haven?t had to touch it since.


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OK I was probably thinking of the SD7 as you said. I'm not sure what you mean by QD head. Would the hoses and ends I have work on the SD-7H15 without needing extra parts or modifications? Do you just have to swap the back of the compressor over? Is there a gasket to worry about?

Sounds like both compressors will cool but you aren't seeing the RPM's get pulled down when it kicks in.

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[82DMC12]

I found this service manual for the SD-5 compressor, which, on page 27, suggests that if you are replacing the accumulator only, to add 1.5 oz to the compressor to make up for what was lost/settled into the accumulator. That's easy enough.

I'm seeing PAG 46, 100, and 150 oil. I guess 150 is only used on a particular GM compressor from the 90's. Should I add 46 or 100 if I don't know what I've already got?

[DMC5180]

QD head comes with gasket. It is the closest to the the original SD5 head type. The ports are vertical ( inline with Filler plug) Bolt torque is 22 lbf. You can mount the compressor with the ports horizontal like OE configuration. I chose to install Vertical due to the Service port locations. 69127


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[DMC5180]

I found this service manual for the SD-5 compressor, which, on page 27, suggests that if you are replacing the accumulator only, to add 1.5 oz to the compressor to make up for what was lost/settled into the accumulator. That's easy enough.

I'm seeing PAG 46, 100, and 150 oil. I guess 150 is only used on a particular GM compressor from the 90's. Should I add 46 or 100 if I don't know what I've already got?

I used PAG 100

I bought my compressor and replacement head from www.coldhose.com that was 6 years ago though.


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[82DMC12]

Thanks for the details.

Did you use a regular white GM orifice tube or did you use the black "variable orifice tube" that some were selling back in the day? I have a black one currently installed (I think).

Do you happen to know how long the bolts for the back plate are? That website sells them in 40, 45, and 55 mm lengths but they don't specify on the page which compressor/head uses which. I can call them tomorrow if you aren't sure.

[DMC5180]

Years ago I bought a Hervey hose kit that came with the variable Orifice tube. I used the VO tube but not the Hoses. Some years later DPI offered a Hose kit I preferred using a fitting system I had familiarity with it from my Work.

Unfortunately, I don?t recall the bolt length. I ended up getting the appropriate length bolt at my local Hardware store. You?ll have to measure the stack up dimensions to the face of the head surface and add 10-15mm for length.

Or just buy all three to CYA [emoji6]

My compressor build spec is CO4708C (chinese sanden) double V-belt ( black pulley/clutch assembly)

USA Sanden version is 4708C (I think)

[82DMC12]

Years ago I bought a Hervey hose kit that came with the variable Orifice tube. I used the VO tube but not the Hoses. Some years later DPI offered a Hose kit I preferred using a fitting system I had familiarity with it from my Work.

Unfortunately, I don?t recall the bolt length. I ended up getting the appropriate length bolt at my local Hardware store. You?ll have to measure the stack up dimensions to the face of the head surface and add 10-15mm for length.

Or just buy all three to CYA [emoji6]

My compressor build spec is CO4708C (chinese sanden) double V-belt ( black pulley/clutch assembly)

USA Sanden version is 4708C (I think)

Nice, thanks for the additional info. This one looks like the right thing, right, but it needs the QD head sold separately?

https://coldhose.com/collections/compressors/products/new-oe-sanden-sd7h15-double-v-belt-a-c-compressor?variant=35532296126624

[DMC5180]

That looks like the correct configuration. You just have to swap to the QD head sold separately $25

You can also do a cross reference check to the CO4708C P/N I have.


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[WHO1DMC]

I'm using the white GM orifice tube and for around 3 bucks it works great. I'm using the original hoses and had to trim off some leftover manufacturing junk so the fitting would go on and not crush the thing. But all n all not bad.




Dave B.

[DMC5180]

You could go with this one. It comes with the QV head ( horizontal ports)

https://coldhose.com/products/new-sanden-style-sd7h15-flex-a-c-compressor-with-5-1-4-double-v-belt-clutch


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[82DMC12]

Thanks guys, I decided to upgrade to the 7 piston 4708 compressor while I have the system in a state of discharge right now. Wasn't looking to spend extra money now that I'm 95% done with a frame-off restoration but as they say.... "now's the time".

https://www.acparts.com/product/new-original-sanden-compressor-4708/

[DMC5180]

Even though the 4708 you chose comes with the QD style head. It is missing one thing. The High pressure safety relief valve.

https://coldhose.com/products/sanden-qd-rear-compressor-head

Technically the Delorean system has the High Pressure Cut-out switch. The HP safety relief valve provides an extra level of safety.


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[82DMC12]

Even though the 4708 you chose comes with the QD style head. It is missing one thing. The High pressure safety relief valve.

https://coldhose.com/products/sanden-qd-rear-compressor-head

Technically the Delorean system has the High Pressure Cut-out switch. The HP safety relief valve provides an extra level of safety.


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Hey you are right. Damn. Well my current compressor doesn't have a high pressure relief. You think I should get that QD plate with the valve too?

[DMC5180]

Well it?s up to you, I did just for the extra layer of safety. It?s a CYA thing [emoji6]


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[David T]

If you don't put a relief valve in don't worry, if the pressure gets too high you will just burst a hose. While the relief valve is not required it is good to have. Some systems use a burst disc.

[Ethan Rode]

The only Deloreans not equipped with a high pressure relief valve were the very early cars that haven't had the AC recall done. The HPR valve is either on a block on the condenser, or in the hub with the HP cut off switch near the receiver/dryer.

The HPR valve on the compressor head may interfere with your hoses. It messes with the clocking of the DGo hoses I've use in the past.

Be aware that many "pad style" heads have different size ports. I've seen them labeled as both QD, QC, or SJ. You'll need to slightly enlarge the ID of the smaller hole on a drill press. I can't recall the drill size at the moment.

The regular white or white/black oriface tube is the one to use. The variable oriface tube does not improve performance in my experience.

[82DMC12]

The only Deloreans not equipped with a high pressure relief valve were the very early cars that haven't had the AC recall done. The HPR valve is either on a block on the condenser, or in the hub with the HP cut off switch near the receiver/dryer.

The HPR valve on the compressor head may interfere with your hoses. It messes with the clocking of the DGo hoses I've use in the past.

Be aware that many "pad style" heads have different size ports. I've seen them labeled as both QD, QC, or SJ. You'll need to slightly enlarge the ID of the smaller hole on a drill press. I can't recall the drill size at the moment.

The regular white or white/black oriface tube is the one to use. The variable oriface tube does not improve performance in my experience.


Ohhhh damn you are right! I totally forgot I already have a high pressure relief in this wet/dry glass that came with my Hervey kit a long time ago. This picture is from before my frame-off but you can see the HPR on the side of the black thing. I should be good to go!

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[82DMC12]

Well it?s up to you, I did just for the extra layer of safety. It?s a CYA thing [emoji6]


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I ran into a little snag while putting this back together.

To review: I now have an SD7H15 (4708) compressor which I believe has a QC head without the provision for a HPR valve. My hoses fit perfectly fine and leak-free to the compressor and the included head. However, I am going to replace my Hervey mess up front and I want to have the HPR valve on the compressor if that is possible.

I ordered the QD head from coldhose.com and fit it this morning to the compressor.

On re-installation of the hoses, I found the suction hoses fits normally but the hole in the head for the discharge side is slightly smaller than the hose requires. Taking some measurements, I find the old QC head has ID of 16.41 mm on both suction and discharge sides. The QD head has suction ID of 16.41 but the discharge is about 15.4 mm. The hose are both a 15.9 mm connection! Thus the discharge hose will not connect up with the QD head.

I reached out to coldhose this morning who said they "could not locate a compatible head with the HPR provision". They said the QD head is model-specific so it probably would not work in a custom application. I am reaching out to another Sanden distributor to see if they can figure something out.

Has anyone else ran into this? I'm not going to replace the hoses over this issue because I could always get a condenser block with the HPR in it and be done with it but if there is a different head that works that would really be ideal.

And, perhaps this information helps someone else in the future.

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In this picture, you see the port size of my hoses - both S and D hoses are the same size










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Here is the QC head that came with the 4708 compressor - both ports are equal size and work with my hoses. The QD head has a slightly smaller discharge port (about 15mm). Not good in my situation!

[DMC5180]

Interesting, sounds like Hervey used the same port adapter fitting for both hoses.

Most systems typically use a smaller diameter discharge HP hose. Typical system is D -8 (1/2?). S -10 (5/8?) which is consistent with the slightly different port diameters.

Any possibility increase the port diameter or have the QC head drilled and tapped to accommodate the brass relief valve. You can see the spot where it go in casting.

This issue didn?t come up with my installation, as I didn?t use the Hervey hoses.

Btw, Ethan mentioned needing to drill the head port slightly larger in has last post here.


What about trying the GV head. ( horizontal ports like the original with HPR) looks like it has two large ports.

https://coldhose.com/products/sanden-gv-rear-compressor-head


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[82DMC12]

Interesting, sounds like Hervey used the same port adapter fitting for both hoses.

Most systems typically use a smaller diameter discharge HP hose. Typical system is D -8 (1/2?). S -10 (5/8?) which is consistent with the slightly different port diameters.

Any possibility increase the port diameter or have the QC head drilled and tapped to accommodate the brass relief valve. You can see the spot where it go in casting.

This issue didn?t come up with my installation, as I didn?t use the Hervey hoses.

Btw, Ethan mentioned needing to drill the head port slightly larger in has last post here.



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Hervey did a lot of questionable things. But anyway....

I only need the discharge side to be about 0.75mm larger ID and my hose would fit. I could probably wrap sandpaper on a dowel and enlarge it with enough finesse and polish it smooth with 300 and 600 grit. That might not be too bad a job to modify. I'd probably try that before tapping the QD head since I don't have a set of SAE taps.

All that said, I did talk to a Sanden distributor tech in Texas. He said honestly the industry has moved away from HPR valves because, duh, they vent freon to the atmosphere which apparently some people have a problem with. Instead they just rely on the high pressure switch and as a backup they might have a heat-sensitive "fuse" that will blow if the system gets too hot. He said if the HPR blows, there's a good chance the compressor is already damaged anyway. That was his take on it and he suggested just running with the high pressure switch and let it do the job.

Not quite sure which direction I'll go yet.

[DMC5180]

Check my previous Edited post. You were probably writing when I resubmitted it.


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[82DMC12]

Btw, Ethan mentioned needing to drill the head port slightly larger in has last post here.


What about trying the GV head. ( horizontal ports like the original with HPR) looks like it has two large ports.

https://coldhose.com/products/sanden-gv-rear-compressor-head


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Ah yes I see Ethan did say that. Been a few days since I read it and now I found out for myself.

I looked at GV head but discounted it because the ports are not in the same locations on the head as the QC/QD. I don't know if that's actually a problem or not. When I asked Coldhose and acparts.com both said they couldn't find a QC with HPR offering. I didn't ask if they think GV will work.

I'll give it all another look tonight. Tiny problem but I'll figure it out!

[DMC5180]

Nothing a 41/64 drill bit won?t fix .640. The hose fitting is 15.9 mm = .625. (5/8)


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[82DMC12]

Nothing a 41/64 drill bit won?t fix .640. The hose fitting is 15.9 mm = .625. (5/8)


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Unfortunately, the hole doesn't go all the way through the head at the same diameter. It reduces quite small like to 1/8" at the bottom of the hole. I'm afraid a drill press would be required to avoid bottoming out the hole. Or, since the hose only goes into the hole like 1/8" deep, I could try to dremel the ID just enough to fit the hose inside. Hmm. Nothing is simple!

[DMC5180]

Is the bottom of the hole Flat? Usually it would just be tapered to the drill that made it. But I guess they could have use flat face end mill. You only need to deep enough for the fitting to sit against the head not through it.


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[82DMC12]

Is the bottom of the hole Flat? Usually it would just be tapered to the drill that made it. But I guess they could have use flat face end mill. You only need to deep enough for the fitting to sit against the head not through it.


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Here are a couple more pictures. I think it's flat at the bottom. I will have to look at my bits since I think 1/2" is the biggest I have and stepping up to a 5/8" would be too big a bite without a couple of step up bits in between. Wish I had one of those big letter bit sets!

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New QD head







Existing QC head with new HPR
69180

[DMC5180]

Unfortunately Letter drill sizes don?t go that large. Home use drill bit sets don?t usually go above 1/2 inch. You usually have to buy individual bits when larger than 1/2.


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