A/C Compressor RPM Limit?

[MJFUR]

Does the A/C compressor have an RPM limit?

69 Chrysler 300 with functioning OEM A/C (R134) until recently. Just started to trouble shoot, but one of the changes I recently made was changing the transmission shift point from the stock 4000rpm to 5000rpm to better align with the cam/engine rebuild. Did I inadvertently cause a new problem? TIA

 

[Mr C]

Cop cars came with A/C shut offs.

However, I cannot reliably recall the details, but I seem to recall that they were related to high speed extended operation and not "launches"...getting old sucks.

 

[Davea Lux]

RV2 compressor will probably no be able to handle 5000 RPMS. They do not do well on R-134a to start with and adding extra RPMs is a self destruct waiting to happen. Some cop cars with the pursuit option had an extra toggle switch to disengage the compressor for extended full throttle operation.

Dave

 

[MJFUR]

Per this, Charger and Charger R/T were available with Automatic Transmission and 3.23, 3.55, 4.10 axle ratios.
https://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1969/69_Charger0024.jpg

Per this, A/C was available on the Charger and Charger R/T with 440/Automatic.
https://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1969/69_Charger0016.jpg

Anyone know what the shift points were in a Charger? I'm guessing higher than the 4k RPM of the Chrysler's.

 

[Big_John]

Does the A/C compressor have an RPM limit?

Have you ever heard of anyone blowing one up because of high RPM? I haven't.

 

[CBODY67]

The a/c cut-out switch started to happen, as I recall, in the 1972+ cars, which had a/c compressors which ran all of the time, even when the main system was punched "OFF". They needed more power to the wheels on those low CR engines during pursuit activities, so cutting the compressor "off" was the easiest way to do that.

There WAS an old "tale" about cutting the RV2 compressor off "at rpm" as to the sudden release of tension on the matched a/c belts knocking them out of their pulleys. Turning the system off or on, "at rpm". I never tried that as I didn't want to get the blame for the belts coming off!

BUT, for the short time the car is at 5000rpm at WOT, I doubt that would have contributed to the kaputment, by itself. It DOES drain power, though! Sandens can easily tolerate higher sustained rpms and more of them, taking less power to run them, too. Just look at the rpms modern engines hit at their WOT shift points.

Just some thoughts and observations,
CBODY67

 

[MJFUR]

I have 12v to the low pressure switch, but not out. (Was this switch added/required for the R134 conversion?) I know it's not OEM.

I don't have the tools/gauges required to work on the A/C so I will need to take it to my buddy's house for further diagnosis.

I was just trying to understand that if the leak IS from the compressor could the 5k rpm have been the culprit.

Thanks for the help.

 

[CBODY67]

That low pressure switch on the receiver-drier was just that, a switch to kill power to the compressor clutch if the gas charge in the system got too low. Somebody might have replaced it with a cycling switch when they did the R134a swap?

 

[USSMOPAR]

There was never an rpm limit for the rv2 compressor, they are very indestructible.
If there is a problem with an rv2 compressor after being rev'd up there is a problem with that particular unit. If the belts are coming off at rpm when the clutch cycles there is alignment - installation - hardware issues - period.

Cop cars had a pressure switch inline with the power feed for the a/c clutch that attached into the high side of the ac system on the compressor to protect the compressor

It's in the parts books.

AC was avail on 383 road runner 4 speeds...etc

 

[CBODY67]

There were some somewhat obscure 4-spd combinations that would not allow factory a/c. 440 4-speed Chargers in a particular model year was one.

Might the issue with the "rpm limit" have been related more to the type of oil in the system and its lube qualities after a certain compressor rpm? For engines which Chevy put in pickup trucks (circa 1969 or so) which could have deeper rear axle ratios as a normal situation, they used a larger diameter compressor pulley. Same diameter pulley was also used on Z/28s with factory a/c too. Related to keeping the compressor rpm in a "sweet spot" for good cooling and "reasonable" rpm levels. Noticeable difference in pulley diameter.

The other side issue with 4-spd factory a/c restrictions could be the orientation of why the car had a 4-spd in the first place . . . drag racing. In some cases, racers pulled the factory a/c off the cars to save weight. Then consider the possibility that higher rpm levels would be used in these races, too.

Enjoy!
CBODY67

 

[It's better in a letter]

The engine will "let go" before the compressor. The electric pressure switches are there to prevent the compressor from running if there is too little refrigerant in the system. The lubricating oil for the compressor is carried by the refrigerant. A secondary switch can and was often used to remove the parasitic load of the compressor when full performance was needed.

 

[CBODY67]

The engine will "let go" before the compressor. The electric pressure switches are there to prevent the compressor from running if there is too little refrigerant in the system. The lubricating oil for the compressor is carried by the refrigerant. A secondary switch can and was often used to remove the parasitic load of the compressor when full performance was needed.

On RV-2 Chrysler a/c systems, where was the "other" switch placed in the system, especially one without the low pressure switch? Just curious.

I know that some GM cars of the 1990s would turn off the compressor when heavier engine loads (and more throttle amounts) were used, temporarily and that many Fox-body Mustangs/Ford Fairmonts had alternator cut-outs when under power, but had never heard of Chrysler doing any of those things in the 1960s.

The alternator cut-out was discovered in an extended range pursuit by some state law enforcement people when the cars suddenly started getting weak from low battery voltage, as they were at WOT for so long.

Just curious,
CBODY67

 

[It's better in a letter]

On RV-2 Chrysler a/c systems, where was the "other" switch placed in the system, especially one without the low pressure switch? Just curious.

I know that some GM cars of the 1990s would turn off the compressor when heavier engine loads (and more throttle amounts) were used, temporarily and that many Fox-body Mustangs/Ford Fairmonts had alternator cut-outs when under power, but had never heard of Chrysler doing any of those things in the 1960s.

The alternator cut-out was discovered in an extended range pursuit by some state law enforcement people when the cars suddenly started getting weak from low battery voltage, as they were at WOT for so long.

Just curious,
CBODY67

I am not speaking specifically of Mopar, all AC systems use one or more switches to control it's function.

 

[CBODY67]

I am not speaking specifically of Mopar, all AC systems use one or more switches to control it's function.

Thanks for that clarification. As I recall, prior to about the 1969 Fuselage cars, there was not a low-pressure cut-off switch should refrigerant get low. Such determinations were made when the system did not cool as well as it should, not by switches. On our '66 Newport Town Sedan, when the cooling got a lit "warm", that meant it was 1lb low on R12, so it got recharged for another year. These were ALL systems which used the EPR-type valve to modulate compressor operation, as the compressors ran all of the time, unlike the cycling A-body and aftermarket systems.

Remember, too, that on the earlier (1950s-era) Chrysler a/c systems, the a/c compressors had no cut-off switches. The compressors had no magnetic clutch on their pulleys, so if the belts were on the compressor pulley, the compressor was running. So it was not uncommon for owners to remove the belts in the "off season".

Enjoy!
CBODY67

 

[MJFUR]

Update - system was low. It held a vacuum. Recharged and working correctly, blows 40F air.

Used an ultraviolet light and can detect just a minuscule amount of green on the expansion valve seam and a speck or two on the condenser. Unfortunately other substances glow green under UV light as well, so not sure if what I do see is an actual leak. I cleaned them off, will see if they return. I guess I would classify this as something smaller than a pinhole leak. It took 2 1/2 years to leak out.

I'll keep better records moving forward with time and system air temp to narrow it down.

Thx