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Old 07-04-2022, 06:48 AM   #1
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AC high pressure switch

I am repairing a locked-up compressor on my 04 American Tradition. I have replaced the compressor, evaporator, dryer, and expansion valve, flushed the system etc.

Now my question. There is a high pressure switch on the high side outlet at the compressor. I assume this is for cycling the compressor off to maintain the R134 at its upper design limit.

The switch is a normally closed design and specs show open at 225PSI, closed (or reset) at 175 PSI. This seems to be unusually low pressure for a refrigerant system so I wonder if it is part of the condenser fan speed control. ????

At any rate the switch is 19 years old, I dont trust it, and I would like to replace it but it is a Freightliner part, obsolete, only 10 or so left in existence, and price is $200 plus. There are many other freightliner switches available in the $30 to $50 range but they run at a higher pressure like 300 high 250 low. Infact most all of the other switches run at a higher range of 300+ PSI.

Any "AC exprts" out there that have any experience in this area and would like to shed some light on this?
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Old 07-04-2022, 09:35 AM   #2
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I’m far from being an expert but I usually put back the same spec that I took out.

I work on the theory that they paid a lot of high dollar engineers to cipher out what needed to be installed.

I’m sure you’ve tried googling a cross reference number
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Old 07-04-2022, 11:25 AM   #3
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When replacing #103930-01-716 a few years ago I used 032-0036, online it's $76
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Old 07-05-2022, 05:27 PM   #4
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The above switch controls the compressor fans 0ff 175 on 225. The high pressure binary switch 10393012708 , I used was 032-00048 has a low limit (25-31) & a High limit (427-483)
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Old 07-06-2022, 08:02 AM   #5
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Quote:
Originally Posted by Al10453 View Post
The above switch controls the compressor fans 0ff 175 on 225. The high pressure binary switch 10393012708 , I used was 032-00048 has a low limit (25-31) & a High limit (427-483)
Thanks for the info. If I understand your feedback, that switch on the compressor High side is used to control the condenser fan speed (which on my coach is a 2 speed hydraulic motor). The part for my unit is very rare and Freightliner wants $200+ for it. There are a lot of other Freightliner similar switches but at different limits. So if this just for fan speed control substituting a different switch with a setting of 273/225 vs 225/175 not that big of a deal.
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Old 07-06-2022, 08:16 AM   #6
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A lot has changed in the RV dash cooling world since 2004...newer refridg. cooling gases use higher pressures, so compressors and pressure switches are different .....also curious as to how your rig handles the condenser cooling fan interface--in that era, many units still used mechanical wax valves to control hydraulic fan motors with no dash AC interface, vs newer rigs with electronic controller and a built-in interface circuit for remote electric fans????
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Old 07-06-2022, 10:54 AM   #7
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A lot has changed in the RV dash cooling world since 2004...newer refridg. cooling gases use higher pressures, so compressors and pressure switches are different .....also curious as to how your rig handles the condenser cooling fan interface--in that era, many units still used mechanical wax valves to control hydraulic fan motors with no dash AC interface, vs newer rigs with electronic controller and a built-in interface circuit for remote electric fans????

My system is R134a which is the most common type for vehicles. I think Ive heard that all electric cars are using a newer 1234YF ??. Hard to keep track these days.


Anyway, as to how the fan speed is controlled is a complex question on bigger class A units. Apparently is combines with driving load and AC load. Dont have a wiring diagram of this area to learn more about it.
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Old 07-06-2022, 10:57 AM   #8
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PS, cant edit my reply. But that last sentence was a question on OK to substitute
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