Minimum compressor RPM

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Bailey28
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Minimum compressor RPM

Postby Bailey28 » Thu Jun 25, 2020 2:30 pm

I installed a Sanden SD5H14 heavy duty into an El Camino with a stock small block Chevy 350.

The a/c works well and I get vent temperatures of 38 degrees F driving down the road.

However when I come to a stop the idle is very rough with the compressor engaged. Some kind of vibration is happening where I can feel it though the entire car. Without the compressor running there is no vibration.

Pressures on a gauge set reveal 45psi low side and 240 psi high side while idling in park on a 90 degree day.

I used the Alan Grove component brackets which secure the compressor. The 3/8 V belt has 1/2" of deflection in the center and the pulleys are aligned very well. The belt wraps half way around the compressor pulley.

I noticed when the compressor is running at idle that the belt whips and vibrates a bit between the water pump pulley and the compressor.

The crank pulley is 6.25" diameter and the Sanden pulley is 5". The engine idles at 650 in drive and the compressor rotates at 825 rpm when the vibration occurs.

Question, is there a minumum rpm for the Sanden compressors? I could not locate anything in literature or searching. If I raise the rpm the vibration goes away but it's hard to hold the car stopped with the brake at that point. Any ideas?
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Cusser
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Re: Minimum compressor RPM

Postby Cusser » Thu Jun 25, 2020 5:17 pm

I think you need to bump up the idle 200 rpm when the AC is on.

You might need to rig up a mount for a solenoid of some sort, install a solenoid to the throttle arm. When you kick on the A/C, it
will boost RPM at any rate you adjust the solenoid in the bracket to.
Solenoid should be easily found at parts store. Making and adapting the
bracket to hold the solenoid may be tricky, but it may be a piece of
cake too. Anyway, that's what I would do.

With my 1988 Mazda truck, the factory carburetor had an idle-up solenoid. Now that it has an aftermarket Weber carb, I just set the idle higher (like 950 rpm) and leave it there year round (Arizona).
Bailey28
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Re: Minimum compressor RPM

Postby Bailey28 » Thu Jun 25, 2020 6:03 pm

I do in fact have a solenoid installed and it does kick up the throttle to where it idles at 650 in gear. If I go higher on rpm the vibration gets worse before it gets better.

I can only go so high on engine rpm in drive before the brakes won't hold the car stopped in traffic. 900 is about the max but its like power braking the thing.

I may have to switch out the crank pulley for the slightly larger stock diameter pulley to get the compressor where it doesn't vibrate.

This is my first experience with the Sanden compressor. I purchased an original Sanden as well, not a knock off version.

Should I look at getting an idler pulley installed between the water pump and compressor?

Would the refrigerant charge have anything to do with a low rpm vibration? Stock R12 fill was 3.25lbs.. I have 2.25lbs of r134a in it now. (70%)

The R4 that came off vibrated as well, the belt on that one looked like a guitar string strumming away.
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bohica2xo
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Re: Minimum compressor RPM

Postby bohica2xo » Thu Jun 25, 2020 9:27 pm

Bigger crank pulley is the answer. The R4 you replaced had more displacement than the Sanden does. A bigger crank pulley will help low speed cooling as well.

.
Al9
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Re: Minimum compressor RPM

Postby Al9 » Fri Jun 26, 2020 5:40 am

You could also try this if it fits.

I think that 7 pistons instead of 4 (the R4) or 5 (the SD5) could smooth things further.
Even smoother operation from a 10 cylinder double acting piston comp (Denso or Seltec designs for example).

I understand that the virus thing is making getting specialty goods a very hard if not impossible task (that's also why i eventually decided to keep a spare new compressor, just in case it's "long gone and no longer made" by the moment the "poor little thing" dies). But
I get vent temperatures of 38 degrees F driving down the road

is (especially the driving down the road part) a sign that a compressor is (or also "is getting", due to wear) undersized for its task. You should be getting ice cold air all the time, ideally. And if things start to get too cold, it just cycles off and comes back on later.
Last edited by Al9 on Sat Jun 27, 2020 2:56 am, edited 1 time in total.
Bailey28
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Re: Minimum compressor RPM

Postby Bailey28 » Fri Jun 26, 2020 5:51 pm

Great suggestions so far.

Getting a new compressor is not going to happen unless this one breaks.

If I reinstall the stock diameter 8" pulley I will turn the compressor 1040 rpm with an engine rpm of 650 in drive... If I bump up the idle in drive to 700 the compressor will turn 1120 rpm.

Also.... as a side note, how difficult should the Sanden compressor be to turn by hand with the engine off? Reason I ask is because a friend had one and before he installed it I swear I could turn that thing by hand with very little effort. It was a knock off 508..

My compressor is almost as difficult to turn as the R4 that came off. I can turn it but it takes all I got. No noises when running or turning it.

I found this in reference to Sanden's performance chart. it depicts 1,000 rpm as the start of their curve. Looks like I will switch to the larger pulley and report back.
https://www.sanden.com/objects/SD5H14_Performance.pdf
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bohica2xo
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Re: Minimum compressor RPM

Postby bohica2xo » Fri Jun 26, 2020 8:31 pm

The 8" pulley should help.

If you ever do want to swap compressors, use the V7 compressor. OEM mounts exist. It has similar displacement to the R4, and is variable displacement - which provides evaporator pressure control.
Al9
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Re: Minimum compressor RPM

Postby Al9 » Sat Jun 27, 2020 2:48 am

Careful not to get above 6000 rpm continuous and 7000 rpm peak though (compressor shaft rpm). That's why i suggested a different compressor instead of a larger crank pulley.

Bailey28 wrote:Also.... as a side note, how difficult should the Sanden compressor be to turn by hand with the engine off? Reason I ask is because a friend had one and before he installed it I swear I could turn that thing by hand with very little effort. It was a knock off 508..

My compressor is almost as difficult to turn as the R4 that came off. I can turn it but it takes all I got. No noises when running or turning it.

Depends upon whether you rotated the shaft with the compressor attached to a fully charged system or not. Any healthy compressor gets really hard to turn by hand if it's compressing something that isn't air at atmospheric pressure. Especially in hot weather. I once rotated my Delphi CVC unit in 50F weather and i could rotate the clutch hub with my pinky finger, consistently. Not joking. Tried it again in the subsequent summer with 90F weather and it immediately got hard as a rock as soon as the swashplate went full tilt. No difference with your SD5 except that it's already full tilt as soon as you touch it since it's a fixed displacement unit.
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bohica2xo
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Re: Minimum compressor RPM

Postby bohica2xo » Sat Jun 27, 2020 6:22 am

Over speeding the compressor is not much of a worry. Iceman may have seen an overspeed failure (he works for Sanden) but I never have. American hot rodders have been testing that upper limit for decades.

Given the known OEM pulleys for the 5.7 I would say his pitch line on that 3/8 belt is probably a 1.3 : 1 overdrive. Unless he is bracket racing with the A/C on, I don't see a lot of 6,000 rpm upshifts.

FYI, the 3/8" belt is capable of doing the job, but most OEM stuff had the 15/32" belt on the compressor. Do you have a pulley groove big enough for a larger belt?
Bailey28
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Re: Minimum compressor RPM

Postby Bailey28 » Sat Jun 27, 2020 4:47 pm

No worries as the car is not a street racer. If the engine goes past 3,500 rpm with me driving it something is wrong! With 2.73 gears cruise rpm at 60 is 2200.


The engine pulleys will handle a 10mm 3/8 belt. Any larger and the belt rides up out of the pulley outer circumference.

That's good to know about the compressor resistance.

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