B-body factory air heater boxes - Question

[gtx6970]

On a factory air equipped 1966-70 B-body.
Why do some have the circular vacuum delay valve on the bottom of the box and some don't ?
I remember my old 1969 GTX with a/c had it.

This valve ?

I have 3 B-body air boxes - 1 has it and 2 do not


1 box I know is a 1967 B-body, the other 2 are supposed to be 1 each 1968 and 1969 B-body

the 67 box doesn't have it , the 1968 box does and the 1969 box doesn't.

It's a thermal delay valve, If I remember correctly it's cycles the compressor in defrost mode untill it reaches a pre-determinded internal box temp

[Chatt69chgr]

could it have been a running change that occurred during the model year?  For that matter, what does the thing do?

[tan top]

mine  had it     ,    SPD   22nd  November 68

[Just 6T9 CHGR]

My '69 R/T doesnt  ----4/30/69 SPD

[gtx6970]

could it have been a running change that occurred during the model year? 

Thats what I'm trying to determine.
Its mounted on the pass side,,, bottom of the box itself

[gtx6970]

bump -
no one else has an air car?

[doctor4766]

My factory air car doesn't have that.

[y3chargerrt]

My Charger has it SPD 1/20/69. Yes it is mounted on the passenger side bottom.

[68r/t]

Mine has it, feb(I think) 68.

[Hemidog]

My 68 has it.

[Troy]

My 68 has it (3/25/68).

Troy

[histoy]

Our '68 Coronet has it - built 10/31/67 and our '68 Charger had it.

[70charger2006]

Unless mine is not correct for my model year, my 1970 has it. 5/25/1970.

[baullz]

My '69 has one build date of 28 February '69