TXV Temp Sensor Clamped or Taped Only to Evap?

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1GCamaro
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TXV Temp Sensor Clamped or Taped Only to Evap?

Post by 1GCamaro »

I'm pretty sure there was never a clamp on my '67 Camaro, and there was only the cork tape / PresTite. But the cork tape holding my new TXV Sensor (the flat rectangular type) gets flexible when the engine is hot and allows the sensor to lose full contact with the Evap tube. Is there an official clip/clamp for this car -- or would it be OK for me to put a hose clamp around the tape to hold the sensor in place (not too tight, just right) ??
tbirdtbird
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by tbirdtbird »

A pic would sure help here.
Having said that, the sensing bulb must be in direct contact with the evap exit tube, else the TXV will not perform well at all. This has always been the rule. The sensing bulb should never be on the bottom of the tube, the side or the top is OK.
You can use a small hose clamp lacking anything else, but don't tighten the snot out of it. In many cases there is a spring steel clip that holds the bulb on, this allows for expansion/contraction of the tube. A hose clamp does not. It would be best to get the correct clamp.

Once properly fastened, insulate. Personally I dislike the Pres-Tape immensely, just try to get it off later.
We use small sections of the high quality soft black foam rubber used to insulate plumbing pipes, not the stiff stuff. We use zip ties to hold it on
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Tim
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by Tim »

Hose clamp, re-tape.
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1GCamaro
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by 1GCamaro »

I've seen the springy-type clamps on others but never saw one on this car - but it does seem to need one. The tape is wrapped pretty tightly and in several layers but still flexes too much when warm. I could clamp it on the outside of the tape to keep it snug, but understand it would be best to clamp before taping - or clamp and use the soft plumbing insulation. I have some of the stiff stuff and will look around for the softer more flexible type described, which sounds cleaner than more of the Pres-Tape. For the time being I suppose I could zip-tie over the existing tape/sensor to keep things nearer to optimum until I do it right.
1GCamaro
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by 1GCamaro »

Using a regular hose clamp, I definitely won't get it too tight. Should I somehow pad or cushion part of the clamp to allow for expansion/contraction?
tbirdtbird
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by tbirdtbird »

Not sure how well that will work. Just clamp it and wrap it.
There is no way that sensor wasn't mounted metal-to-metal originally
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Tim
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by Tim »

The probe has to be directly placed against your suction line. The hose clamp is fine, it's just to hold the sensing bulb in place. Then wrap with prestite tape. Tape is just to cover the bulb from warm/hot air messing with sensing bulb sensing.
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1GCamaro
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by 1GCamaro »

Thanks! It was definitely metal to metal to begin with, but only recall tight tape holding it in place. It was fun removing the old Pres-Tite (razor blaze and kerosene). Will be clamped and wrapped to make it right.
Al9
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by Al9 »

Leaving the sensing means exposed to the hot engine bay will make the TXV "hunt" in certain circumstances as the control charge cyclically migrates between a cold region and a hot region.

I've seen a Denso patent where it seems that their "sensing tube in suction port" style block TXVs seem to do that when they're placed sideways or downways rather than upways. The sensing tube has an internal pathway to the disc. The gas charge condenses inside the tube (due to the cold suction gas), then drops by gravity inside the disc where the engine bay heat turns it into a gas again, and the cycle repeats, making the valve hunt.

Part 447500-1620 used in many Jap applications in a sideways mount, for example, features black thermal insulation material on the disc in order to prevent heat from the engine bay from affecting valve operation due to sideways placement of the valve. By contrast, part 447500-1600, featuring a naked disc, is only found in applications featuring an upright TXV.

Bottom line, by all means, make sure to thermally insulate that sensor pretty well, or the valve will hunt severely (unstable vent temperature the most immediate sign, unstable pressures the other).
Dougflas
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Re: TXV Temp Sensor Clamped or Taped Only to Evap?

Post by Dougflas »

do not use zip ties. they stretch after a while. As mentioned, use a hose clamp and then cork tape
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