Automotive Air Conditioning Information Forum (Archives)

drhill on Mon July 09, 2012 3:54 PM

Year: 1973
Make: Rolls Royce
Model: Silver Shadow
Engine Size: 6.75
Refrigerant Type: R-12
Ambient Temp: 98
Pressure Low: 60
Pressure High: 245
Country of Origin: United States

Hello everyone.

I am coinverting this vehicle back to R12 from a previous R-134a conversion. All oil has been measured (esther oil) and has new TXV and Drier. I vacuumed the system and it held over 24 hours.

The shop manual calls for 3.5 lbs of R-12 for a full charge on this car. The readings above were obtained with only 2.5 lbs of R-12, which is where I stopped as vent temps were already poor (above 60 degrees). No leaks in the charge hoses etc...

To me, these reading look like an overcharged system or air in the system...but according the shop manual I'm not overcharged and I can't imagine there is air in the system? Any ideas?

As a side note, when the system is running, the sight glass shows white and foamy...

This overall scenario happened when trying to charge with 134a as well.

Thank you for your assitance.

mk378 on Mon July 09, 2012 6:11 PM

Fan clutch may be weak, or otherwise restricted airflow. Put water on the condenser and see if the pressure drops a lot. You have foam in the sight glass because it is not fully charged.

Edited: Mon July 09, 2012 at 6:12 PM by mk378

drhill on Mon July 09, 2012 6:34 PM

I will try the water on the condenser...thank you. I can also try to take digital temp readouts from various points on the condenser if that helps?

This scenario has played out with the stock fan clutch and fan as well as the dual electric fan setup I now have on the car - which moves much more air at idle and slow speeds than the oe clutch fan.

JJM on Mon July 09, 2012 7:26 PM

A sight glass showing foam on an R-12 system is usually an indication the receiver dryer desiccant has broken down. Was the dryer NOS or recently manufactured? I would not want to use a NOS dryer from 1973 because it's desiccant is well past due.

Not sure, but maybe the foaming is the result of POE oil? Not sure, since systems I've used POE on didn't have a sight glass.

I'm not so much concerned with the high side pressure as I am the low side pressure. Were those readings at idle or 1,500-2,000 RPM? If idle, ok, if not, there's definitely a problem... possibly a bad TXV assuming the system is not over oiled.

Does the Rolls have a POA?

Joe

drhill on Mon July 09, 2012 7:44 PM

hello Joe, readings were at 1500 rpm or so...

The Rolls did have what the shop manual calls a "suction Throttling Valve that appears to have been disabled. Supposedly this is common in these cars as parts no longer exist to control the valve as factory intended. I had a local Rolls specialist verify that this appears to be the case.

I did just replace the txv and drier a few months ago along with a new compressor (GM style A6 was oem on these cars)as the previous one was slowly failing to produce high side pressure.

Hopefully there is an easier answer but I suppose worst case I can recover the r-12, flush the system, replace the txv and drier again, and charge with proper oil qty and freon. That's a lot of work that I would like to avoid if possible!

bohica2xo on Mon July 09, 2012 7:47 PM

You can't evaluate a system that is undercharged. The foam simply means you don't have enough liquid yet.

Pull the engine speed up to 1500+ rpm, and get the full charge in to the system. Spray the condensor down with some water, and put the cabin fan on the lowest speed. Do waht it takes to get a full charge in.

Once you have a full charge in the system, then you can evaluate the performance.

Idle the system for 5 minutes with the cabin fan on highest speed, doors open. Record ambient temp. / vent temp / High side psi / Low side psi.

Run the engine speed up to 1500 rpm, doors open, fan on highest speed. Record ambient temp. / vent temp / High side psi / Low side psi.

Post those results, and we can go from there.

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.

JJM on Tue July 10, 2012 1:34 AM

I seem to recall Rolls using a lot of GM parts in their A/C systems, long after GM stopped using them, so if there's an STV - it looks something like a POA, except on the end there's vacuum diaphragm - it's probably a GM STV and those can definitely be rebuilt, or a rebuilt purchased. So the question is, what's controlling the evaporator from freezing up? It would be almost scandalous to have a Rolls with a compressor clacking on and off! Most unnerving to the distinguished chauffeur or passenger.

But as Bohica mentioned, there needs to be a full charge to diagnose.

Joe

drhill on Tue July 10, 2012 2:49 PM

drhill on Tue July 10, 2012 3:33 PM

No problem - I will load in the full charge on Friday and report back.

You are correct - this whole AC system appears to be GM. Rolls Royce issued a service bulletin many years back regarding this issue. Silver Shadow STV bulletin

The problem I see on my car is that Rolls had one of their electric motors controlling the STV and parts are missing and the motor is non operational. My car is not a concours restoration but a nice driver - and function is most important to me.

I see that the STV has definately been disabled - I am not sure about the retro kit being installed - I will have to investigate and I will install if not done so. Frankly, where I live and with the kind of driving I do (all city driving in Palm Springs - 115 with 10% humidity today!), I would feel lucky to have my evap freeze!

I know we can at least evaluate the system when I get it fully charged and go from there.

bohica2xo on Tue July 10, 2012 4:56 PM

That assembly looks more like a hot gas bypass valve from even earlier models than the STV equipped GM cars.

STV & POA valves are controlled by feedback pressure, not with a cable. Hot Gas Bypass valves use a cable & cam:



That picture is one I took under the hood of a 1960 Cadillac.

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.

JJM on Wed July 11, 2012 12:57 AM

It does look like a hot gas bypass valve from the old GM A5 systems... minus the hot gas line (gotta love the brute force methods they employed back then).

Since evaporator freezing is probably not an issue, but by any chance did you try Classic Auto Air? They rebuild hot gas bypass, STV, POA, and VIR/EEVIR valves. They probably can rebuild your Rolls valve too, if you want the system to function (and look) as original.

Let us know how you make out with the full charge though.

Joe

drhill on Wed July 11, 2012 8:34 PM

Hopefully will be able to charge and test tomorrow am...I'll also take a picture of the STV/POA that is on the car...it does look like a version of the later GM stuff - not the pic above, but I am by no means an expert!

I am very curious to see what happens with the charge and what you guys think.

Thanks again for all of the input so far!

Edited: Wed July 11, 2012 at 8:34 PM by drhill

drhill on Thu July 12, 2012 3:38 PM

Ok, put in the extra pound of r-12 for 3.5 lbs total...the OEM recomended charge.

Outside temp: 93
Outside humidity: 45%

engine warmed up, car at idle, 5 minutes to stabilize:
Low Side: 60
High Side:250
vent temp: 70

rpm incresed to aprrox 1500-1700 rpm and allowed 2 min or so to stabilize:
Low Side: 50
High Side: 300
Vent temp: 66-68 (it felt a bit colder than this, maybe my temp gauge is slow)

Returned to idle and allowed 3-4 minutes to stabilize:
Low Side: 62
High Side: 255
Vent temp: 70

some notes:

I drove the car for 20 minutes after the testing and maintaining 50-55 mph, achieved vent temps of 58 degrees

The sight glass in the accumulator still showed some white with system running and full charge. I could not see any bubbles.

With the system running, the suction hose near the compressor was very wet, but not icy cold. The high pressure hose running from the compressor to the condenser contains the high side fitting which was very hot, i had to shut the car off and let the fitting cool before I could remove the high side fitting even with a rubber glove on.

The receiver/dryer currently on the car is a bit smaller than the oem piece.

When I replaced the compressor and the dryer a few months back, I followed the shop manual recomendation for oil fill qty if these two pieces were replaced. I did not flush the system at that time so I do not know how much oil was still in the rest of the system. Could there be too much oil in the system?

Thanks again for all of the help you guys have provided.

Edited: Thu July 12, 2012 at 4:15 PM by drhill

bohica2xo on Thu July 12, 2012 8:39 PM

It could have too much oil in it. More to the point, this is a reverse conversion, so if you did not flush it the oil is contaminated with the oil you used with the 134a. After you flush it, the entire oil charge goes in the compressor sump.

I would be inclined to put the OEM size receiver on it after flushing all of the components (except the compressor) clean & dry. Drain the compressor sump since this is a reverse conversion, flush it out with the oil you plan to use in the system then re-fill it with the specified oil charge.

Once you get it back together, duct tape the gauges to the windshield and drive down 111 at 60 mph or so to see how it is doing.

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.

JJM on Fri July 13, 2012 12:40 AM

With those vent temperatures, you basically have no air conditioning.

I'm leaning towards the TXV. The excessive suction side sweating at such low humidity leads me to believe the evaporator is being flooded with refrigerant. Is the TVX internally or externally equalized? (External has two sensors). Is the TVX sensing bulb firmly clamped to the evaporator tailpipe outlet, and was there clean metal to metal contact?

Try blasting the TXV with hot and cold (you can use boiling hot water and ice water) while the system is operating and note the pressures. You should see a pretty good swing.

To further test the TXV, run the engine at around 2,000 RPM and allow the pressures to stabilize. Now partially cover the condenser to increase high side pressures to 350-375 PSI (be careful here). If the low side pressure rises, the TXV is probably bad.

Joe

drhill on Fri July 13, 2012 12:51 PM

Thanks guys...I will try Joe's txv test first since I can do that with the car as is...sounds like either way I'll likely have to open the system up again for something. Fortunately Ester oil was used in the conversion and I used that same oil in the compressor replacement.

The txv has one sensor line running to the evap outlet and one tube running to the STV - a pressure line, not a sensor.

I'll report back after the txv tests. I also forgot to snap a pic of the STV...Since I'll have everything apart I'll look into proper actuation for that or the less desireable cycling clutch conversion.

thanks again!

JJM on Sat July 14, 2012 1:15 AM

That tube running to the STV is the equalizer line. My preference is NOT to have an externally equalized TXV when an STV is removed. It is important, however, that this line be exposed to the refrigerant and not plugged in any way, otherwise the TXV will not function. Is it possible this port ended up getting plugged with the STV gutting?

My feeling is to replace the TXV and STV if you want the best possible cooling. Classic Auto Air should be able to help on both fronts (and can ensure the valves are calibrated for R-12), especially if you kept all the parts from the STV gut.

Joe

drhill on Mon July 16, 2012 2:41 PM

I replaced the txv recently as well. I was not the one who disabled the stv so I am not sure what was done internally...I know the txv was and is working in some capacity but I will perform the tests and check it out properly.

I will call Classic Auto Air...my concern is the that mechanisms to control the stv are long gone...they would have to help me devise another way to control them. OEM was an electric motor from what i can tell. Worst case, I'll use the official rolls conversion kit to cycling clutch or another suggestion from Classic Auto Air.

After testign the txv, I may recover the r-12 and thorughly flush the system and check out the stv and txv...maybe the stv is clogged up or was improperly disabled?

If I choose to continue on with the disabled stv, can I switch to a txv without the external pressure regulation?