As we previously indicated, we are installing A/C in our 1960 MK2 3.8. We have taken a different route that we have seen. In that we are driving the compressor from the alternator (recently upgraded). We installed a tandem pulley on the alternator which sits in the same spot as the generator. On top of that sits the compressor. Driven off the second pulley groove on the alternator. The first groove of course is the belt from the crank and the water pump. Got the A/C charged and seem to be working ok. BUT when we rev the motor above idle we get an awful sound. With the A/C off (compressor not engaged) motor revs fine.

We have looked and looked and it sure sound like something is hitting something. But for sure the fan blades are clear, the belts look like they are moving freely. We see no belt slapping as the belts are tensioned properly. SO what is it? Could it be a belt slapping??

We even put a strobe light on the belts and fan and can see no abnormal actons.

Perhaps a broader question. Is there an issue with this setup, which we have not seen tried before? Driving the compressor from the alternator.

Ideas anyone.

Is there any way I can upload a short video??.

Thanks
jjsandsms

 

The joys of trying to Modify perfection.
Is the Compressor new? If used have you checked the bearing on the pulley? Does the compressor have a clutch plate drive or is it direct?
Try to isolate the noise by taking off the drive belt from the alternator to the compressor.If the noise is still there then it is not the compressor.
Is the belt from the alternator to the compressor aligned correctly. If it is slightly out you might be getting some rubbing of the belt against the inside of one of the pullies.

 

My first thoughts are the compressor clutch and the fan in the alternator. A stethoscope can be useful in finding the source of sounds, but be careful that it doesn't become caught up in the pulley belts.

Does the noise change if you increase/reduce the tension in the belts?

 

Thanks for the replies so far. To answer a couple of questions. The compressor engagement is driven by the temperature control on the evaporator. Compressor is a new Sanden 508. When the temperature control shuts of the compressor regulating the cabin temperature, and when the entire system is off. NO noise when the compressor is off. engine revs freely.

Alternator is new.

Water pump allegedly new when purchased car recently.

Alignment of the two belts looks good. Tension is tight.

A/C works great, engine idles smooth until it revs above about 1500 when noise starts and noise gets louder the higher we go.

I searched videos on you-tube for fan belt slapping. Most deal with serpentine belts but several reference the sound coming from a bad chain tensioner. The sound I am getting does sound a lot like those addressing timing chain slap in some of the videos. And the noise seems to be coming from the water pump front chain housing.

BUT if by chance why would a timing chain tensioner have issues only when the compressor is on. I have had the car for over a year and it runs and revs freely, of course with now compressor until now.

So it seems the noise is directly related to the extra strain put on the motor when the compressor is on.

Have not yet adjusted the belts tensions as with the configuration it is very difficult.

My configuration, driving the compressor from the alternator seems to be unique with regard to XK engine installation. A friend has an e-type and an early 120 coupe, both have had A/C added. Their configuration has the compressor mounted where the generator was, and the new alternator sitting above it where I have the compressor. So they have one belt from the crank to the waiter pump to the compressor. And a second belt from the compressor driving the alternator. I have seen this configuration on other XK engines when doing research on adding A/C

The more traditional approach would be to have a separate belt driving off the crank to the compressor and the other belt of course driving the water pump and generator. But there is just not enough room to add a dual pulley on the crank and would require idlers. The water pump fan is just too close to the radiator. One A/C vendor here in the States actually uses one belt to drive everything by using a series of idler pulleys.

So my configuration may have a generic issue

As one pointed out "The joys of trying to Modify perfection"

Will keep everyone posted as we work thru this.

Hey it gets hot and humid here in Florida and I just love this car, so we will try to get this sorted somehow.

Thanks
jjsandsms

 

Just an observation. We doubt the alt. front bearing will take the load.

 

I agree with CF. could you try driving the compressor off the crank and the alternator off the compressor? Compressors relay do put a heavy load on things.

 

Yes that has been our concern since we started this project. Perhaps that's why we have not seen this configuration before, yet tandem pulleys seem to be quite available, so there must be a use for them (PS pumps?), but just maybe not driving A/C compressors. The alternator is a Delco 10SI, a common unit used for upgrades. Quite inexpensive and plentiful as rebuilt units. But at least for now, not sure that is the cause of the noise as the sound does not sound like a bearing issue.

For info. The inside pulley groove on the alternator drives the compressor, the outside of course is from the crank/water pump.

So it maybe back to the drawing board, as A/C is used here probably 10 months a year, so want reliability and not having to change alternators often..

Thanks
jjsandsms

Sure wish there is a way to upload a video so others can hear the sound.

 

My personal prejudice would be to drive everything from the crank.* However, modern serpentine belt systems are effectively tandem drives and seem to work. If the noise resembles that of a bearing groaning under excess load, might one or both belts be too tight? And, of course, it's not always safe to assume that new components function correctly.

*Swap to XJ crankshaft damper and pulley. Swap to an electric fan, slimline or pusher.

 

Hi,
I would say that one of the 2 alternator belts is the problem The Alternator pulley is small and has very little belt wrap (friction surface compared to the other pulleys). The alternator is also driven at (if I remember correctly) 1.2 to 1.5 times engine RPMs. When adding the compressor load to the alternator pulley you have a good chance for one of the belts to slip. The compressor load can be up 7Hp but normal loads are in the 3-4Hp range. Your statement " as you rev the engine higher than 1500 RPM's the noise get louder" indicates to me belt slippage, more slippage at higher RPM's. I would think if it was a bearing the noise would be there all the time, with or without the A/C on.
I hope this helps!

 

Yes and thanks for the discussion. I will try one more time to adjust the tension as well as the alignment of the shorter alternator to compressor belt. However it is looking like my little experiment is not going to work. Probably why I have not seen this configuration as I have been mentioning.

I do agree the best situation is two belts off the crank, one for alternator and water pump/fan and the other just for the compressor. Good thing we don't have traditional power steering pumps!! My car does not have power steering. I do believe that I can add a second pulley on the crank, but the fan has to be moved towards the radiator about a 1/4 inch to allow for the second belt clearance, and the tips of the fan have to be shortened by about 1/2 inch to avoid hitting the top housing of the radiator.

The other solution as suggested is to drive the alternator from the compressor, which is the configuration I am familiar with on two cars in my neighborhood.

Either option will require an idler pulley. So out again if the radiator and the condenser.

Thanks
jjsandsms

 

jjsandsms,

Just to add another thought, an inexpensive mechanic's stethoscope is very useful for locating the source of engine bay sounds. The cheap one Harbor Freight Tools sells works great.

Alternately, a long screwdriver or socket extension can be used, with one end held to an ear and the other end probing various points on the alternator, compressor, water pump, etc. Just take great care not to allow the probe to come into contact with moving pulleys, belts, fans, etc.

Cheers,

Don