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  1. #16
    Join Date
    Mar 2011
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    Quote Originally Posted by keviekev70 View Post
    Nice, but shouldn't the TXV bulb be installed upstream the trap and external equalizer?
    That is a good question. My thoughts are, if you were speaking practically, in real world operation, the exact bulb location does not make too much of a difference. Provided it is securely fastened and at least marginally insulated. (I believe air conditioning and refrigeration is not an exact science and what works on one job, may not work on another, experience and experimentation on start up and maintenance check ups are what works)

    My father says he has seen an instance (a large capacity valve) on a particular installation, where the bulb capillary was pointed downward, above the txv power element, and the valve sort of "hung open" and over fed. Rotating the bulb 180 degrees fixed the problem.

    From memory, a Carrier recommendation was to install the bulb a minimum of two piping turns (if possible) from the evaporator outlet to ensure good refrigerant mixture before the sensing element. Also, to locate the bulb on a vertical section of piping (if possible) and if horizontal, to locate the bulb 45 degrees from the bottom of pipe to protect against oil insulation from true temp and possible liquid flowing along the bottom of pipe.

    I decided to dig out some books and review. I don't have any links because I prefer books. But anyway, the old Trane Reciprocating Air Conditioning Manual suggested placing the txv sensing bulb upstream of the equalizer line as keviekev70 suggested. Reason being from a possible liquid leak-thru from the high side to the low side via the equalizer line, influencing and falsely throttling down the valve. I myself have not experienced this, possibly due to modern expansion valves being manufactered with better and more precise designs. The Carrier system design piping manual had no real details on the exact location of the sensing element, however the IOM for the Carrier 38AE condensing units suggested via an evaporator piping layout diagram the appropriate location for the txv bulb as upstream of the external equalizer line. The McQuay refrigerant piping manual also depicted the txv bulb upstream of the external equalizer line.

    To summarize, technically it is correct to install the piping in that manner.

    Having plenty of hands on time with this installation however, I can say that it performed well.
    Last edited by AiResearch; 01-04-2013 at 07:30 PM.

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