Could a Car A/C pump be converted into a compressor

This topic has 10 replies, 9 voices, and was last updated 11 November 2020 at 23:56 by Nick Wheeler.

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5 November 2020 at 10:01 #505421
Clive Foster
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@clivefoster55965
The recent thread on compressor selection got me wondering if a car air conditioning pump could be made into a useful quiet compressor.

Plenty of folk, me included, have built reciprocating compressors around redundant industrial refrigeration pumps or lorry brake air pumps. Mine worked well but, being reciprocating, were noisy. Basic A/C pumps are rotary sliding vane types so should be quiet.

Finding proper data on actual pump performance is beyond my Google-Fu but it seems typical displacement is around 100 – 120 cc and input output pressure range around 45 to 150-175 psi. Power consumption is said to be around 3 hp / 4 kw.

Plugging the numbers into a very handwaving analysis the 3 hp power consumption suggests something around 8 cfm at over 100 psi could be available when run at 6,000 rpm. Drop it down to 1,000 rpm it could be driven by 1/2 hp gives perhaps 1.5 cfm. Plenty for running a model or spraymist / fog buster type cutting oil supply although 1 cfm at 600 rpm from 1/3 rd hp drive should be more than enough for cutting oil supply.

Silding vanes need lubrication so there would have to be some sort of drip feed lubrication on the input side, air tool feed bottle I guess, and your application would need to be tolerant of a little oil in the air supply. Can't see an issue with models or spraymist / fog buster.

Modern sophisticated ones are swashplate pumps which probably wouldn't do well unless more oil than desirable were used.

Dunno how well the economics stack up. £30-£40 from a breaker for a pump then there is the motor and all the other bits. Possibly something north of £100 – £150 if you have to buy everything. But it you just happen to be standing in the way of a cheapy with a dead pump on its way to the skip ….

Clive
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5 November 2020 at 10:01 #27752
Clive Foster
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@clivefoster55965
5 November 2020 at 11:21 #505436
Perko7
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@perko7
I've had a similar thought about power steering pumps, wondering if they could be re-purposed. Not sure how they work though. Some diesel cars also have vacuum pumps to power the brake booster, has anyone pulled one of those apart to see how it works?
5 November 2020 at 11:24 #505437
Nick Clarke 3
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@nickclarke3
The issue with repurposing any refrigeration pump is that it is lubricated partially or totally by the refrigerant but air does not do this and a compressor is a total loss system anyway.
5 November 2020 at 11:51 #505444
J Hancock
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@jhancock95746
Really falls to what you want the compressed air to do.

Usihg f or painting or breathing air, rules out oil anywhere in the system for domestic applications.

Now , what are you left with , diaphragm for low pressure, dry piston for high pressure.
5 November 2020 at 16:46 #505482
Chris Evans 6
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@chrisevans6
Posted by Perko7 on 05/11/2020 11:21:46:

I've had a similar thought about power steering pumps, wondering if they could be re-purposed. Not sure how they work though. Some diesel cars also have vacuum pumps to power the brake booster, has anyone pulled one of those apart to see how it works?

Know nothing of power steering pumps but did run a series three Land Rover diesel with an electric vacuum pump for the brake servo. It got rid of the stupid butterfly flap set up in the inlet manifold and the engine ran well. Cost around £70 and an hour or two to fit triggered from the brake light switch. Hella U28 pump if anyone needs to know.
9 November 2020 at 14:01 #506199
Dave S
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@daves59043
Pretty sure American off roasters do something like this (air con pump as compressor).

IIRC they can then lower tyre pressures for certain sections of a trail with the ability to pump them back up as required.

Dave
11 November 2020 at 12:44 #506763
Derek cottiss
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@derekcottiss41883
would a range rover suspension pump not work easier ?
11 November 2020 at 15:36 #506797
Oily Rag
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@oilyrag
One thing to be aware of with pumps, and especially when working with air is the type of pump. Basically the two types of pumps are external compression type and internal compression type. A centrifugal compressor meanwhile is a third type which exchanges speed for pressure and is effectively deemed to be neither internal nor external compression type!

As an example a tapered screw compressor is an internal compression machine whilst a parallel screw compressor is an external compression machine. Vane type pumps are generally considered to be external compression type but this definition is dependent upon internal construction and porting arrangements. 'Flat head' A/C pumps (typically made by AC Delco) are what you need to look for, these are based on a reciprocating piston design with a LP and HP stage and pressure is controlled by a pre set spring valve. These pumps were common on USA spec MG, Triumph and Jaguars of the 1970's and 80's. The later type A/C pumps of the Denso sort are swash plate rotary pumps.

How about a supercharger?
11 November 2020 at 22:50 #506907
Clive Foster
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@clivefoster55965
Another thing pushing me towards trying a car air con system compressor as an air compressor is an upcoming project that could be most easily engineered using a pair of electro- magnetic clutches to control a 2 speed belt drive.

Car air con compressors come with nice electromagnetic clutches on the drive end and used ones are reasonably cheap. If I'm buying units for the clutches anyway it makes sense to try and use the compressors too.

A bit of extra oil in the air won't worry my spraymist systems but I suspect I'll need to find vane type ones. Swash plates probably need more oil and piston one so old as to be unobtainium now.

Clive
11 November 2020 at 23:56 #506917
Nick Wheeler
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@nickwheeler
Posted by Derek cottiss on 11/11/2020 12:44:03:

would a range rover suspension pump not work easier ?

They're only intended to run for a few seconds at a time to adjust ride height. And once the suspension is pumped up, very little air is needed to do that. Car air suspension systems use very similar pumps, and they all fail very quickly if a leaking air spring isn't repaired ASAP.

One might work if you want a quick, cheap and quiet blow gun for a machine – I have an Omega one to try – but they won't run air tools.
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