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Discussion Starter #1
Dear all,


I have a 94 33 1.5 IE. It had a bad AC compressor when I bought it so I have installed a new Sanden AC compressor. AC works but I realised that it is taking too much power from the engine.

I noticed that new micro cars (ex: Suzuki Alto 54HP, Tata Nano 38HP) have very small engines but have very good AC setups.

I was thinking whether their AC compressors have to be pulling a lot less power from their already wheezy engines.

Has anyone else given a try on such a setup for their boxer engines?

Interested to hear your ideas.

Thank you


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Hi,

The smaller engines like you've mentioned are equipped with A/C compressors that have
lower rated delivery, therefore they require less power from the engine.
Regarding the effectiveness: the A/C system in those cars are designed to R134a refrigerant
from the start, and they're have larger condenser and evaporator surfaces
to cope with the less effective refrigerant gas. As I heard the expansion valve at the
evaporator side also provides a higher flow rate in the R134a systems.

Using R134a in your 33 would require a slightly oversized evaporator (which is very small)
and condensers to get the same cooling effect that the original R12 gas would be able to provide.
Also air flow of the two factory condensers are very limited, which is also a negative factor,
and this limited airflow needs to be aided by the two cooling fans (usually running all the time)
thus putting a significant load on the alternator (16 to 20 Amperes).

The compressor's power demand may increase when the condensers are not capable
to reduce the temperature of the compressed refrigerant gas effectively, and that creates
excessive pressure at the discharge side of the compressor which struggles to overcome it.
Sometimes the trinary switch interrupts the compressor clutch supply when the pressure
gets too high.

Excessive refrigerant quantity in the system could also require more power from the engine,
while the effectiveness of cooling drops significantly.

So in short: a smaller compressor itself won't solve the issue, yes the engine may regain
some power when the A/C is running, but the price will be (more) reduced cooling capacity.
 

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Discussion Starter #3
Hi,

Thank you for the reply.

The condenser was modified by previous owner to a front mounted one with 2 fans attached to it.
These are 12" or 14" fans so the area is quite large compared to the Nissan I have. (See photo)

This had detrimental effect on the radiator so I had to mount additional small electric fan to keep the engine cool. After that, the car never overheated even at a very hot day, stationary with full AC on.

The factory evaporator is in a sorry state of course. I want to replace that with a modern evaporator suited for R134a.

The compressor I have is a Sanden SD5H11 which is a piston type compressor.

My idea is to replace that with a smaller AC compressor.

Today I had a chat with local AC shop and I was told that these smaller compressors are scroll type, not piston type and that design is less energy consuming it seems.

Hope they are not trying to rip me off and that seems like it would actually work. As evaporator will be and condenser is R134a compatible, that should work, shouldn't it?

Expansion valve has to be addressed too then, which is a good point my friend.


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Hi again,

I think the SD5H11 is a bit smaller in delivery capacity compared to the original SD508,
108 vs 138 cc / revolution. In case of a scroll type compressor the delivery rate should be
near to (or somewhat higher than) the original. It matters a lot at idle speed.

Long time ago after some consultations I've found that the condenser surface should be similar
to the radiator of the engine in order to work efficiently, especially under hot climate conditions.
Something like this:
936720


936721


This was a condenser from an Alfa 156 (which is designed to operate with R134a).
IMHO anything smaller than this will not provide adequate cooling capacity.

In this position the grille can't be put back in place, but if the condenser is lowered by 5 to 7 cms,
it fits. (This requires extra mounting ears on the lower front cross-member, and also
require to replace the condenser related AC hoses.)
 
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