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TXV probe line length?

drhill on Fri November 09, 2012 3:14 PM User is offline

Year: 1973
Make: Rolls Royce
Model: Silver Shadow
Engine Size: 6.75
Refrigerant Type: R12
Country of Origin: United States

Hello AC experts, I recently had a local AC tech tell me that the "leads" on my TXV were too long and could cause problems with the function of my AC system. I have never heard of this before - my TXV has a pressure line to the old STV area and the temp probe line to the EVAP line. They are quite long - much monger than needed and coiled near other hot items under the engine bay. Is there any truth to this?


Dougflas on Sat November 10, 2012 6:11 AM User is offline

the length makes no difference but you do want to keep them away from excess heat.

mk378 on Sat November 10, 2012 12:27 PM User is offline

What Dougflas said. The pressure line is just transferring gas pressure so it doesn't matter (Hot gas in an open part has the same pressure as cool gas). The length of the temperature probe line is accounted for in the calibration of the valve.

Edited: Sat November 10, 2012 at 12:28 PM by mk378

NickD on Sun November 11, 2012 8:00 AM User is offline

Are you having problems?

drhill on Mon November 12, 2012 1:19 PM User is offline

no problems, did have some previously, but had too much oil in the system, so I had it flushed - local shop gave me that advice on the TXV but it didn't sound right to me. He might have meant that the longer the probe line is the more chance it has to pick up heat from nearby engine parts....I think I will make sure that it's not touching or close to anything hot and call it a day...

Thanks for the expertise everyone!

ice-n-tropics on Thu November 15, 2012 6:46 PM User is offline

The Royce has one of the few applications of a suction line heat exchanger to increase the sub cooling of the liquid refrigerant R-12 upstream of the expansion valve. Bentley has the same A/C system made by ARA in Dallas, Texas.
The SD510 compressor on the Royce does not require excessive oil because it has an internal oiling passage for the front bearing and shaft seal.
RR enthusiasts recognize that Royce was THE ENGINEER and not the commercial guy, therefore never call your car a Rolls.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

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