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Converting back to R12? Upgrade condenser? Pages: 12

DaveMcKenz on Sat August 13, 2011 4:32 PM User is offline

Year: 1993
Make: Bentley
Model: Continental R
Engine Size: 6.75L
Refrigerant Type: R134
Ambient Temp: 90
Pressure Low: 35
Pressure High: 245
Country of Origin: United States

Hello,
I have been working on improving my a/c performance. I received the above car with several leaks, which I gradually found and fixed. It was previously converted from R12 by unknown method. I have replaced or rebuilt the entire refrigerant system except the condenser in the past year. Hoses rebuilt w/ barrier, new green o-rings, txv, drier, fan clutch, compressor, evaporator, etc. It is finally performing very well at highway speeds, where I get 38 degree vent temps (low speed) in sunny, 94 degree weather. Unfortunately, I have to park the car in direct sunlight all day long. It is dark green, and although I just added 35% Formula One Pinnacle window tints, my interior temp usually starts at 115 degrees. In the stop and go driving from there, my vent temp only makes it to 45 degrees with a maximum vehicle speed of 30 mph.
My question, if I want to improve low speed performance, should I revert to R12 or should I upgrade the condenser and keep the R134? Also, since I currently have ester oil in the system, and it was flushed prior to installation, could I just swap refrigerants and do nothing else?
Thanks in advance,
Dave

70monte on Sat August 13, 2011 5:44 PM User is offline

Do you know for sure that the condensor is the original one or has not been replaced when it was first converted? If it's original and you want to stay R134a, I would probably replace it but your vent temps of 45 degrees during stop and go driving is still very good so I don't know if it's really necessary.

If you go back to R12, you will have to flush the entire system because the two different types of oil used between these two refrigerants are not compatable. You will somehow have to get all of the oil out of your compressor which I don't know how easy that would be.

I personally would leave things like they are for now and maybe down the road if you have to replace the entire system again for some reason, you can then decide to do a switch.

Wayne

DaveMcKenz on Sat August 13, 2011 5:55 PM User is offline

Thanks, Wayne. I feel quite certain the condenser is original. One strategy I was considering, order the largest PF condenser that I can mount, with custom hoses and keep R134. I had read on this forum that ester oils can be used with R12. It occurred to me that a simple refrigerant exchange could solve all my problems. I know mineral oil is standard for R12, but since there is already ester oil in it, maybe I'm OK. It is apparently your experience that this is not OK.
Thanks,
Dave

bohica2xo on Sat August 13, 2011 7:01 PM User is offline

Dave:

I can't say I have been under he hood on that particular model, but in general Bentley V8's of that vintage have a very tightly packed engine bay. You could drop marble anywhere under the hood and it probably would still be wedged in the engine bay 1000 miles later.

Early 90's Bentley cars had mechanical drive fans, but the last one I looked at the fan itself looked like it was borrowed from an MGB.

Is this a turbo car? If so, there is always a a fight for airflow & real estate in the heat exchanger stack. Placing the condensor first gives the best cooling, but the turbo designer wanted the cold air first for his intercooler...

There are some changes that can be made. A larger / more effective condensor is great if you have the room. Upgrading the airflow can sometimes be done without too much work.

Get us some pics of the fan, heat exchanger stack, etc. - and describe the placement, order, etc.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

DaveMcKenz on Sat August 13, 2011 8:55 PM User is offline

Thanks Bohica,
The turbocharged engine is very tight and very hot. I just had a new viscous fan clutch installed with some improvement. I have measured for a universal PF condenser and I think I can make some improvement there. I was just wondering whether any pros here have reverted to R12 while keeping the ester oil and just changing refrigerants. If not then maybe over the Winter a condenser upgrade is in my future.
Thanks,
Dave

JJM on Sat August 13, 2011 11:39 PM User is offline

I probably would've kept that vehicle R-12. After all, this is a Bentley we're talking about.

If the condenser is the typical tube and fin, it probably isn't quite enough for R-134a, though your performance is extremely good considering - both vent temps and pressures.

Since I know very little about these vehicles, what controls evaporator temperature? I seem to recall Rolls Royce used the A6 compressor for quite some time, and not sure if the Bentley uses it as well. Rolls Royce also used POA valves and VIR for some time after GM stopped using them. For some reason, I just can't imagine a Bentley or Rolls Royce owner having their A/C compressors clack on and off like some Kia, though with that big V-8 you would hardly notice... but the clacking noise while valet parking!

If there is a pressure switch that controls evaporator temperature, have you adjusted down the cut out pressure?

If you want the ultimate in performance though, switch back to R-12 AND install a parallel flow condenser.

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com




bohica2xo on Sun August 14, 2011 12:50 AM User is offline

Dave:

From a purely technical standpoint, 134a is actually capable of moving a little more heat per pound of refrigerant. The problem is moving the heat out of the refrigerant once it leaves the compressor.

I would be inclined to change the condensor if it is a tube & fin unit, and run 134a. If you can't make it cool with that, then consider the R12 swap.

I would like to know more about the fan assembly. Metal? Plastic? Blade count? Upgrading the airflow may add a little noise, but it can add performance to both the A/C and the intercooler. Would not be the first time the NVH group handicapped the cooling system.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

DaveMcKenz on Sun August 14, 2011 10:27 AM User is offline

Thanks Joe. There is a freeze switch in the evaporator core. It is adjustable. I fooled around with the upper and lower limits for a while with a glass of ice water. It shuts off at 33 and turns back on at around 36 degrees. It was very frustrating to set.
Thanks Bohica, the mechanical fan is supplemented with two 9" electric fans, 4-blade, plastic, Sanden units. I removed them and spent an hour or so cleaning the condenser with an aerosol coil cleaner and also Simple Green with repeated soaks and rinses. I remounted them and verified correct rotation.
I am not sure why the previous owner converted to R134. I am the second owner of the car with only 27000 miles.

Edited: Sun August 14, 2011 at 10:28 AM by DaveMcKenz

bohica2xo on Sun August 14, 2011 12:24 PM User is offline

Dave;

Sorry, i was not very clear. The mechanical fan is what I was asking about. Not all belt drive fans are created equal, and I have been testing a few lately...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

DaveMcKenz on Sun August 14, 2011 12:41 PM User is offline

B.
The mechanical fan is a 7-blade plastic unit. The viscous clutch is new and I did see an improvement over the old fan clutch. The condenser has a 1" gap on the sides and top between the radiator and condenser. I think I could fashion a seal of some kind here if that would help.
Thanks,
Dave

bohica2xo on Sun August 14, 2011 3:05 PM User is offline

Improving the seal around the condensor edge should help some.

What is the diameter of the mechanical fan? Does it rotate the same direction as the crankshaft? Or is it driven from the flat side of the belt?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

DaveMcKenz on Sun August 14, 2011 3:26 PM User is offline

Hi B.
The mechanical fan is 18" (!) in diameter and is mounted directly to the crankshaft via the viscous clutch.
I thought I would pull the front trim and see if I can make a frame covered with foam pipe insulation to seal the condenser to the radiator.
Thanks,
Dave

Edited: Sun August 14, 2011 at 3:31 PM by DaveMcKenz

bohica2xo on Sun August 14, 2011 4:04 PM User is offline

Yeah, not much you can do about that. Crank drive fans are rare in passenger cars. Used in a few COE medium duty trucks however.

To put that into perspective, I have an 18.5 inch diameter steel fan mounted on a viscous clutch. It is overdriven 1.33:1 from the crank with a belt. On a 4.9L I6.

You really need as much static pressure as possible to force the air out of the engine bay after the fan. I haven been testing fan blades, and the current king of SP is the fan from a 2005 GMC Envoy. Looks more like the intake on a jet engine:



Unfortunately it is a reverse drive fan, and will not work on the bentley crank drive.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

DaveMcKenz on Sun August 14, 2011 7:25 PM User is offline

Thanks B.,
I will work on stack sealing. Seriously, I know it sounds irresponsible, but have you ever just swapped refrigerants with a clean ester oil system?
Dave

bohica2xo on Sun August 14, 2011 8:47 PM User is offline

Dave:

from a purely academic standpoint, yes you should be able to pull a long vac cycle under 1000 microns & swap refrigerants.

In this case however you are getting good performance from what is technically a more "powerful" refrigerant. You are close, and may in fact be seeing the equal of OEM performance right now. I rarely favor a conversion, but yours looks very good. Let's see if we can wring the last few percent out someplace, before you swap back to r12.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

DaveMcKenz on Sun August 14, 2011 8:51 PM User is offline

Thanks, B. I'll work on the stack this week and post some pics.
Dave

70monte on Sun August 14, 2011 8:52 PM User is offline

Ester oil is compatable with both R12 and R134a but since you currently have a full charge of R134a in the system, there will probably be too much R134a mixed in the oil to just switch to R12 without flushing the system out.

Maybe someone with more experience than I can give you a definate answer.

Wayne

DaveMcKenz on Sun August 14, 2011 9:09 PM User is offline

Thanks, Wayne,
I understand what you are saying but when the R134 is evacuated the oil removed is also visible and could be replaced. My concern is more about longevity on an R12 system with almost entirely ester oil.
Thanks,
Dave

70monte on Mon August 15, 2011 6:13 AM User is offline

Evacuation does not remove the oil from the system. It only removes the refrigerant. To remove the oil you have to flush the system and replace some things like the accumulator.

Wayne

DaveMcKenz on Mon August 15, 2011 9:50 AM User is offline

I see, Wayne. I knew that evacuation would not remove very much if any oil. It had not occurred to me that the oil itself would retain refrigerant and that would be a problem.
Thanks,
Dave

DaveMcKenz on Mon August 15, 2011 12:31 PM User is offline

Hi, I pulled the front trim off my car to have a good look at the condenser assembly. I turns out to be a serpentine type, not tube and fin. I only have a 1/2" gap between the condenser and radiator on the sides and bottom. All in all, I think I will keep it as is for now. If the really hot weather is too much for it, I will consider going back to R12, but I doubt it. Thanks for all the advice and input.
Dave

70monte on Mon August 15, 2011 5:22 PM User is offline

I think your performance is pretty good and is why I suggested in the beginning to stay with what you have until the time comes when you have to start replacing major components again.

Wayne

JJM on Mon August 15, 2011 11:54 PM User is offline

Serpentine condenser, this explains why your R-134a performance is actually pretty good. If the condenser was tube and fin, cooling performance would with R-134a would be very becoming for a Bentley.

When you replaced the TXV, did you replace it with one from a R-12 equipped Bentley? The superheat differences between R-12 and R-134a is not that great, but since we're dealing with literally a few degrees of unsatisfactory performance, an R-134a calibrated valve might make the difference. Perhaps you can try a TXV designed for a 1994 or later Bentley (likely the year Bentley switched to R-134a), assuming it has all the same fittings. The existing valve can be re-calibrated, but it does take quite a bit of expertise.

The 1/2 gap could be a lot... couldn't hurt to seal that.

I would've still kept this vehicle R-12... this is, after all, a Bentley.

Joe

When considering your next auto A/C purchase, please consider the site that supports you: www.ACKits.com


DaveMcKenz on Tue August 16, 2011 12:54 AM User is offline

Thanks Joe. The expansion valve is new and supposedly calibrated for R134. I will work on sealing my condenser gap this weekend.
Dave

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