Basic Air Conditioning questions

[skysurfer]

I'm in the process of installing a Sanden compressor but since I know little to nothing about ac I need to ask a question or three. Go easy on my lack of knowledge, this is like standing in front of the class without pants. Anyway, my intention is to get the components installed and have my local mechanic pull vacuum and fill.

Working on a burb with rear ac. I need to flush the evaporator on the firewall and the rear unit (the forward components are new).

1: I have read that the initial flush should be reverse to normal flow so am I correct in thinking the evaporator gets flushed top to bottom?

Concerning the rear, I removed the expansion valve from the back and temporarily installed a piece of hose to complete the loop.

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2A: With this done, can I blow ac flush through the lines from the engine compartment and expect a thorough flush of the rear unit?

2B: And am I correct thinking the initial flush should be the larger (upper) of the two lines going to the rear?

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3: And finally, the compressor came with oil but I'll need to add some to the system. Is it ok to add any additional oil to the accumulator?

 

[Snoots]

With the Expansion Valve out of the loop it doesn't matter which way you flush it. Put a new Variable Rate Expansion Valve back in and let your experienced AC mechanic determine how much PAG oil to put in.
Not knowing the capacity of that system I couldn't venture a guess.

 

[skysurfer]

I've been copying the conversion that yevgenievich did in this thread since it's the same vehicle.

https://www.gmsquarebody.com/threads/r4-to-sanden-whith-stock-ac-lines-for-serpantine.22437/

He went with a total fill of 250cc so that's what I'll be doing as well. I'm pretty sure the compressor comes with 200cc in it (need to double check that) but I'd like to know if the additional oil be added to the accumulator?

 

[Poppy 87]

I'm in the process of installing a Sanden compressor but since I know little to nothing about ac I need to ask a question or three. Go easy on my lack of knowledge, this is like standing in front of the class without pants. Anyway, my intention is to get the components installed and have my local mechanic pull vacuum and fill.

Working on a burb with rear ac. I need to flush the evaporator on the firewall and the rear unit (the forward components are new).

1: I have read that the initial flush should be reverse to normal flow so am I correct in thinking the evaporator gets flushed top to bottom?

Concerning the rear, I removed the expansion valve from the back and temporarily installed a piece of hose to complete the loop.

You must be registered for see images attach

You must be registered for see images attach

2A: With this done, can I blow ac flush through the lines from the engine compartment and expect a thorough flush of the rear unit?

2B: And am I correct thinking the initial flush should be the larger (upper) of the two lines going to the rear?

You must be registered for see images attach

3: And finally, the compressor came with oil but I'll need to add some to the system. Is it ok to add any additional oil to the accumulator?

John, you are on the right track, however, I would replace that 30 plus year old rear evaporator core as it appears to have been leaking. As far as you have the a/c system apart replace those parts, flush lines prior to installing new components in the rear. I would have your a/c tech add leak tracer dye when charging system to assist in the future for potential leaks. I assume you will charge the system with r134a refrigerant. Do some research, but the conversion is approximately 75% capacity of the original r12 your truck came with. Good luck

 

[1987 GMC Jimmy]

1. Yeah, I’ve done both directions. With the orifice tube/expansion valve out of the picture, I agree that it doesn’t really matter.

2A/B. I think all this is fine.

3. If it doesn’t give you an exact oil amount on the stickers, you’ll have to dump it in a measuring container and add it up to the right amount lr just start over. Don’t add anything to the accumulator. Add it all to the compressor and turn the clutch by hand about 8-12 rotations before starting the charge process. That’ll get oil in all the proper crevices. Also, like Poppy said, add some UV dye into your oil bottle so you can find future leaks. I do 85% original capacity, and that works well for me, but an I use a Ford Blue orifice tube instead of screwing with the variable POS tubes. If this is a receiver drier/expansion valve system and not accumulator/o-tube, I can’t advise on the best route for an expansion valve. I’m not sure if these systems are different or if these two system styles are being used interchangeably here.

 

[skysurfer]

Thanks Poppy. Your post had me go take another look at the rear evap core and it looks better in person than the pic would indicate. There's light dust on it but that's abut it, and the housing that covers the whole thing has a light layer of dust on the inside but no traces of moisture going to the drain tube. If the cost of the rear unit was just a minor incidental cost I'd go ahead and replace it but the darn thing is $200. The cost of this upgrade has already damaged my wallet more than I care to think about so at this point I would prefer to see if the system holds vacuum and go from there.

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[Dave M]

O-rings need to be replaced to R134A compatible also.

 

[skysurfer]

@1987 GMC Jimmy, this system has the conventional white orifice tube up front, which I'll be changing to the blue one, and the rear has a traditional metal expansion valve which I have a new one.

I've verified the compressor comes with 200cc in it, so at this point I only need to add 50cc to get to the fill level that yevgenievich did on his. (I tried calculating the amount myself but got lost in the details so I'll trust the success that Viktor had with his.) I was thinking the Sanden factory fill was much less and there wouldn't be room to add several ounces to the compressor but 50cc is only 1.7 oz. so I should be able to add that directly to the compressor.

 

[skysurfer]

O-rings need to be replaced to R134A compatible also.

I'm on it. Only problem was there's a certain size of the smaller o-rings used in this setup that the basic assortment from NAPA doesn't contain. Just ordered one of those "18 different size-270 pcs" kits of hnbr o-rings from Amazon which should be here tomorrow.

 

[skysurfer]

Figured I'd post a pic of the flushing device I made. Cost was $12 and holds 48oz. of fluid. Haven't tried it yet but I pressure tested it to 110 psi and plan on using it at 60-70 psi. Still, knowing what pvc can do under pressure I'll wrap it with a heavy blanket while working with it.

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[1987 GMC Jimmy]

At least the flushing liquid smells good if it gets everywhere, at least I think the smell of oranges is good.