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Help needed: 78 Rolls Royce 134 conversion, insuffient temp drop new condenser

Dirkdaddy on Thu September 26, 2013 11:47 AM User is offlineView users profile

Year: 1978
Make: Rolls Royce
Model: Silver Wraithe II
Engine Size: 5.7?
Refrigerant Type: 134a
Ambient Temp: 80
Pressure Low: 35
Pressure High: 210

The patient is a collector car in pretty good shape. Was R12 obviously.
Complaint was the AC would start cold and then get warmer and warmer.

The condenser was tube and fin, designed for R12 and had very close fins, the existing supplemental electric fan was dead.
The vehicle has a narrow grill area, and the unit-body construction limits making any modification for more space in front of the radiator.

I got the largest 134a condenser I could fit, which is still small at 13x22.
Dual 9" quality fans mounted set as pusher mounted directly to condenser switched to run continuous when AC is on (not just compressor)

a Old Air POA valve eliminator and a new expansion valve were fitted as well as 134a fittings, hoses were changed out.
New drier/accumulator
I had to make custom hoses for the new condenser, had them crimped by local shop who does Vintage Air

The shop who sold me the condenser and POA / expansion valve, hoses, fittings etc is a AC only shop and the guys behind counter are old as the hills and have worked there 30 years+
When I mentioned buying flush they said don't bother, just use this PAG oil they supplied that was compatible with mineral oil from the R12, adding the typical 2oz for the condenser and 2 oz for the accumulator. The container indicated it was compatible with mineral oil and either R12 or 134.

I pulled vac to nearly 30 inches (about what my pump can handle) for over an hour. Held vacuum over half hour no leaks.
I charged enough to get the system crank the compressor and and then put in enough 134 to get to about 210 h / 35 L at abotu 80 degrees which using the chart was about where it should be. This turned out to only be about 1.6 cans worth of 134a.

The system was working well, I was getting about 45 degrees at the vent, but it kept going up slowly. After cleaning up and disconnecting the hoses I took on a drive. Outside temp was about 92 and sunny.

The AC started out working great, but after 15 minutes got warmer, about 50. Then 55, then 60, then 65. The engine temp also went up, which is logical as the condenser covers most of the radiator. FYI, the engine has a belt driven fan with a clutch system, I am not sure how hard its pulling but it works normally for typical driving w/o the AC.

I got back to the shop and tested the temps of the in/out on the condenser, the input was 155-160 deg F, and the output was about 140-45. Yes it was hot and not cooling.

Obviously the charge is not getting cooled enough, but I am unsure where to go from here. The owner is not price sensitive, he just wants it to work.

* can't fit any bigger condenser up front. The body/frame of the car borders all sides and already I had to use 90's on hose connections
* a double thick one in could be the solution, if one like could be found or custom made. I have not seen one like that. The R12 condenser was pretty thick about 1.75"
* wondering if I should make a remote AC condenser to add to it in series. Where to mount it is the question, there is some room under the middle of the car but would rely on fan for all airflow there. I have never seen a setup like that, can you have two condensers in a row?

suggestions? Is the oil causing any problems?
Thanks



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Classic and Antique Mechanic

mk378 on Thu September 26, 2013 12:08 PM User is offline

My first thought would be too much oil. You really should flush out all the mixed oil and install the proper amount of 100% PAG.

Air getting warmer as the engine warms up suggests that the heater core is not being fully shut down with the dash control on cold. When the A/C and the heater are allowed to fight each other, the heater will win.

Make sure the condenser is plumbed so gas goes in at the top and liquid comes out at the bottom. Also if you look closely at the construction of a parallel flow condenser, it has an inherent top and bottom. The part with a larger set of tubes in parallel should be at the top. The receiver-drier is also sensitive to flow direction and must be mounted vertically. It is a cylindrical tank with a dip tube to the bottom to preferentially pick up liquid and feed it to the TXV.

Really if cost is no object and you are in a country where it is still legal (the USA being one of them), fill it with R-12. All PAG oil must be removed, as it turns to sludge when mixed with R-12.

Edited: Thu September 26, 2013 at 12:19 PM by mk378

Dirkdaddy on Thu September 26, 2013 12:23 PM User is offlineView users profile

Thanks for response. The system is plumbed up as you indicated with #8 on top of condenser and #6 on bottom, the drier has a directional indicator and is correct.
I understand what you are saying about the interior climate control and heater, but why would the condenser fail to cool even it is running flat out?
Hmm..

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Classic and Antique Mechanic

Cussboy on Thu September 26, 2013 3:02 PM User is offline

Quote
Originally posted by: Dirkdaddy
Complaint was the AC would start cold and then get warmer and warmer.


I'd also check to make sure that the AC clutch is not slipping as it gets hotter. Also mist some water on the condenser, see if that helps, to isolate whether it might be due to insufficient condenser cooling. How's its fan clutch? Don't ignore that either, even if radiator doesn't run hot, the fan does double duty...

Dirkdaddy on Thu September 26, 2013 6:02 PM User is offlineView users profile

I think the fan clutch is suspect, but going to test it. Its a old car, and I don't hear a lot of fan noise or fan flow. You and I are thinking the same thing. Was also thinking of the water test.

Guy I bought parts from thinks the radiant heat from the radiator is heating the condenser He says if it cools intially, the condenser is sized ok. Hmm....

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Classic and Antique Mechanic

Cussboy on Thu September 26, 2013 8:05 PM User is offline

Quote
Originally posted by: mk378
Air getting warmer as the engine warms up suggests that the heater core is not being fully shut down with the dash control on cold. When the A/C and the heater are allowed to fight each other, the heater will win.

Yes, bypass the heater core temporarily or clamp it closed to ensure this is not the issue, as a stuck "flap/door" could allow heat to enter the vent routing.

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