a/c expansion thermal bulb positioning- 66 427

[Harry L.]

Should the expansion a/c thermal bulb be clamped on the upper or lower side of the evaporator tube? thanks , Dutch

[Ray G.]

Re: a/c expansion thermal bulb positioning- 66 427

Hello;
Hope this helps.
Ray
Expansion valve install .jpg

[Larry M.]

Re: a/c expansion thermal bulb positioning- 66 427

Dutch:

The TXV (expansion valve) temperature sensing bulb on my 1967 factory air car is on the underside of the evaporator outlet tube.

Larry

[Harry L.]

Re: a/c expansion thermal bulb positioning- 66 427

Larry, does it make a difference? Have you ever put the bulb on the top of the tube? Did you get better cooling on the bottom? Thanks, Dutch

[Larry M.]

Re: a/c expansion thermal bulb positioning- 66 427

Dutch:

In my opinion the location on top or on bottom makes no difference as long as the thermal bulb is tightly secured against the evaporator outlet tube and the bulb is well insulated with the black insulation tape/putty. Just be certain that the capillary tube from the TXV valve is long enough for the top position.

Original TXV use a J-shaped bulb that fits better in one location than another. If you are using a replacement TXV with a coiled end or cylindrical bulb it probably makes no difference.

Larry

[Tom L.]

Re: a/c expansion thermal bulb positioning- 66 427

The TXV bulb should NOT be placed on the bottom of the tube. Oil may act as an insulator and cause the valve to hunt, a bad thing for operation. It is intended for commercial applications but see the link for a detailed descritption. Personally I usually place bulbs at 4 or 8 o'clock. Good luck!!

http://www.emersonclimate.com/Documents/FlowControls/pdf/Contractor%20Tip%20Cards/Tip%20Card%2008.pdf

[Larry M.]

Re: a/c expansion thermal bulb positioning- 66 427

The TXV bulb should NOT be placed on the bottom of the tube. Oil may act as an insulator and cause the valve to hunt, a bad thing for operation. It is intended for commercial applications but see the link for a detailed descritption. Personally I usually place bulbs at 4 or 8 o'clock. Good luck!!

http://www.emersonclimate.com/Docume...0Card%2008.pdf

Tom:

I won't argue the exact location of the sensing bulb with you. In my opinion, and according to the GM Service Manual, the main condition is that it is tight to the evaporator outlet tube and that it is insulated. But………...

1. Where does the "oil" come from?? There is no oil anywhere near this location for a mid-year car unless the evaporator outlet pipe has a leak. Then it doesn't matter.

2. The St Louis line workers back in March 1967 must not have read that Emerson brochure, cause they put my connection on the bottom. However, the AC has worked since that time (45 years).

However, I am always willing to learn.

Larry

[Tom L.]

Re: a/c expansion thermal bulb positioning- 66 427

I'd think that factory workers were never educated on the details of the a/c systems they installed. The procedures they followed likely only insured that there was cool air flowing. IF it was tested, I don't know if they did.

Sorry I wasn't clear on the oil thing. Unlike our old engines oil travels through the entire system at all times. Refrigeration systems (OOPS, I may have confused refrigeration with A/C. Actually ALL of the principles are the same) oil does travel through the system and at the exit of the evaporator it will likely flow at the bottom of the tube. It is supposed to. One of the problems in our modern "cooling" world is the fact that older oils are not miscible with modern refrigerants but that's another discussion.

Going back to the bulb placement issue, since properly matched refrigerants and oils travel though the system together it is possible, and even likely, that there will be refrigerant that has not completely boiled off in the oil. If the bulb were to be strapped to the bottom of the suction line it will sense the temperature of the refrigerant laden oil. Not the temperature of the suction gas. That's the only issue. There will either be capacity loss or flood-back to the compressor. Neither are good.

Some may say that I'm being picky and that the "old" systems work just fine but this is my trade, I understand it. While some want their cars to be as they left the factory I'd hope that they also want them to be right, not just "correct". Hope I cleared my position up. As always, Have fun!!!

[Ray G.]

Re: a/c expansion thermal bulb positioning- 66 427

[ATTACH=CONFIG]61000[/ATTACH]
1967 aim

[Keith B.]

Re: a/c expansion thermal bulb positioning- 66 427

just so I can relax about it I placed the bulb on the top of the tube on dads car. the AC works and blows cold. should I move the bulb to the bottom. or will it be fine

[Ray G.]

Re: a/c expansion thermal bulb positioning- 66 427

On top is correct. Or on sides if necessary . On the bottom could give false readings and cause erratic function.