Minimum compressor RPM

[Bailey28]

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?

[Cusser]

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]

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.

[bohica2xo]

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.

.

[Bailey28]

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

[bohica2xo]

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.

[bohica2xo]

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]

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.

[Bailey28]

An update for you all:

I removed the underdrive pulley and installed the stock diameter crank pulley. The compressor now turns faster which allows for better cooling at low rpm.

HOWEVER the vibration was still there with the car in drive at a stop. Since the rear of the compressor is supported only on the bottom ears it left the body of the compressor free to vibrate.

I rigged up a 3/8" turnbuckle and attached it to the top rear mounting hole of the Sanden. I then connected the other end of the turnbuckle to a bolt hole on the cylinder head. Using proper spacers to avoid pinching the compressor ears together of course.

IT WORKED. The vibration is almost non existent at idle in gear.

I am now devising an idler pulley system to get the belt slap under control at idle.

[Tim]

Be careful with those ears. They can snap if tension is forced upon them They like a fixed brace better in my opinion. Have had many compressors over the years sent back claiming ear broke. Had one guy the other day claimed the ear fell off. Cast aluminum body/ear, fell off.