Just noticed this the other night. When the AC's on the AC pulley (below the metal looking gray arm) is naturally spinning and the AC works fine. When I turn off the AC (heat) the AC pulley from some reason does this start stop deal and the drive belt tensioner (gray arm looking deal above the AC pulley) kicks up then back down. The AC and Heat work fine.

 

The compressor will cycle in the MAX A/C, defrost, and defrost/floor positions by design.

 

Thanks glc, I had AC off, heat cranked to 90, and it was rapidly starting and stopping though as seen in the video? Is that normal? It doesn't stop just on for a split second then off and back on etc. AC works fine the AC pulley engages and spins continuously without any irregular noise.

 

What selection did you make for where the air comes out?

 

Yes it's normal, all vehicles with A/C does this. It's to keep the seals lubed so the system doesn't leak.

 

When the AC compressor comes on, any air passing the evaporator core is dried out as moisture condenses on the evaporator core .... to later drip on the ground out that tube.

Long ago the compressor didn't cycle in anything but AC modes but then it was discovered that when defrosting, the system does it much faster with drier air like comes out the evaporator core so now when you choose any setting that relates to AC or Defrost, the AC compressor is involved.

My '77 was of the old design ..... one day I wired I in a simple toggle so when I set it on Defrost, I can flip the switch and within seconds, the windshield is clear. It was not designed like that in 1977. I did the same on my '67 Chevelle SS with factory AC in early '80s.

 

My 2000 F150 heat is luke warm, blend door closes completely, new heater-core and rad, 4 coolant flushes slightly better but still not hot. I noticed that the AC clutch is engaging every 25 seconds or so. I realize it's supposed to do this in defrost but it also does it in panel and floor heating selections therefore the air it's blending is colder than the outside air by feel at the blend box. Any ideas?