Clutch cycling switch

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volaredon

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This isn't an a body but I typically get better results here, there aren't any D150 sites that compare to what this site is to an A body....

I'm adding factory AC yan 85 D150.
I have most all the parts off of multiple donors of 80s factory ac equipped trucks. Just missing a few things, have multiples of other related parts.
One thing I don't have, and have seen on some vehicles but not others ... A "clutch cycling switch"
Different than the low pressure cutout switch. I know I need that.
This is a square block, with 2 terminals, and has a capillary tube that slides in along side one of the lines near where it bolts to the expansion valve. It's wired in line with the "hot" lead to the clutch.
How important is this, what happens/don't happen if I don't add this, and run the "hot" straight to the clutch /rather than thru one of these?
 
Evaporator will freeze up and system will quit blowing cold. Essentially serves the same purpose as a low pressure cut-out switch.
 
Have to pop the CD I have of the factory service manual back in the computer when I get home, I thought it showed both the low pressure cutoff switch and the cycling switch on that one.
 
This is basically a temperature control, and I don't know why they don't call it that. It simply drops the compressor if the evap gets too cold. Once an evap starts to ice up it becomes a (literally) a snowball. The thing starts to ice/ frost over, which decreases airflow, and that causes the temp to drop lower which causes more ices, which causes...........and around and around you go
 
I don't run one on my cars but I live in Az were freeze up not common. I just planned on being a human cycle switch if it started to blow warmer while in use.
 
Ok next question
What is the white pastey grease they use with the capillary tube where it piggybacks the main line set?
 
The clutch cycling sw controls the minimum evap temp, to as stated, prevent evap freeze up. The low pressure sw (on the drier, if my memory is correct) will cut off the compressor, if the refrigerant is too low. This protects the compressor from failure due to lack of oil. If it were my vehicle, I would replace the low pressure switch with a dual low/high pressure switch, that will protect the system from high head pressure, due to lack of air flow thru the condenser.
PS: With the thermal clutch cycling sw, make sure you use "thermal grease", not silicon grease. Same stuff as used on the back of the GM ign modules
 
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