The question on which AC compressor to use has come up in my mind and I have been searching around for what compressor to use.

There are the standard Denso compressors as well as the Sanden SD7 replacements offered by places such as Gritfiths, both good choices but also both are reasonably large, reasonably heavy compressors.

Well, I don't need much AC in Europe so have been looking with interest at the Sanden SD5 as it is a bit lighter and takes up less room in the engine compartment, albeit with a smaller capacity.....probably not an issue, but I note with interest that there are scroll compressors (notably the Sanden TRS series) that seem to offer a better result....smaller, lighter, more efficient, less NVH and I figuring why the heck not? I will need to fabricate a bracket to fit the AC mount (the '89 aluminium one) anyway,.

I read on one of the Mazda forums that a guy had replaced his piston compressor with a Sanden TRS9 scroll and really liked the result, alleging that he got equivalent cooling with notably less draw on engine horsepower...sounded good.

Anyone have direct experience with a scroll compressor or need I be a pioneer?

 

Our electric AC systems use a scroll compressor. So yes, we have plenty of experience with them having shipped 500+ systems now. What do you need to know?

 

Hi there Jonny, I know about your systems, I like a lot of what you are doing....and have your fusebox solution on the car and been very pleased.

My question is about conventional engine mounted AC compressors. The historical standard has been the Sanden piston compressors and in my limited experience with them, I have been pretty happy.

I am digging for a new compressor, but considering that I only narrowly decided to put any AC on the car as I am Dutch and AC is not a critical need. I landed a few years ago on the solution being a moderate capacity system using a 964 condenser, coupled with a Kuehl evaporator, thought process being that an OK sized condenser with a good evaporator and a small compressor would be a good combo, albeit undersized if it got really hot (say...Tuscany)



So, started the look for compressor and all the ones "for 911's" are the Sanden SD7 which is on the larger side (or Denso), but I got intrigued by the Sanden TRS09 which seemed to tick all the boxes, is a little lighter and little smaller than the others which gives me a bit more clearance for my ITB's.

But no one uses them in our application...most people I have contacted just come back with the standard piston compressors.

So, long winded ask.....is there any reason NOT to use a scroll compressor? Are they inherently more fragile or more difficult to deal with in some way? Are there installation requirements that need to be taken into account such as their apparent need for higher RPM (the Sanden scroll is rated for 10,000 rpm which would imply a pulley ratio of 1.3 as compared to the standard 911 AC drive of something like 0.8 (max piston compressor RPM tends to be 6000 rpm from what I see).

Building the mount does not worry me at all....it will be tedious but don't see an issue. I have to check and see if I can get a V-belt drive for the scroll, if not, a multi-rib can be done albeit with a custom pulley setup...may be a pain though.

Just overall....why wouldn't I do it? Should I just get the smaller Sanden SD5 piston compressor and live happily ever after (AC wise)?

Thanks for any feedback...

 

Scroll compressors are more efficient than the piston type. This does not mean they are 'more powerful' or provide greater cooling, it means that for the same amount of energy used, they provide more cooling compared to a piston type. Think about that for a minute.

Like most 'systems', the components need to complement each other, so a modern high efficiency compressor requires the evaporator and the condenser to be compatible. Modern AC systems generally use parallel flow technology for the heat exchangers which are much lower volume. That's why a Prius only has 450g of Freon, vs your old clunker that needed 1500g+.

So, the issue might be that if you use the Sanden scroll with the older type tube and fin evaporator and serpentine condenser, you might not get the performance you are expecting.

One thing is confusing me about the mechanical Sanden though, it has a clutch so that it is either ON or OFF. With our electric scroll compressor, it can be controlled for speed, which means that you don't need to waste engine power when the demand is lower (e.g. when the car has cooled down), you can just turn the speed down a bit. You can't do that with a clutch!

 

I have the later 993 serpentine condenser, sounds like that is a good thing and of course the Griffiths evaporator is also serpentine. The on/off nature of an engine driven compressor is just the way it is I guess, no different than the piston compressor, although I must admit the variable speed option in the electrically driven one does sound like a good thing.

I am not hearing any concerns about using a scroll, so I will let fate decide to a fair degree. I will start searching for both the Sanden scroll and SD5 piston, there are a few suppliers but I want to make certain I get the real Sanden and not a knock off, and whichever one crosses my path first is the one I'll buy.....and face it, worst case if the scroll does not turn out, I just swap it out for a SD5 at that point and all I am out is some labour and a few hundred bucks.

I will continue to get any learnings I can and will post anything material here for the benefit of all.....

Thanks!