Accumulator/dryer really cold even when AC is off

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ripcord

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Another question for the group... This may be a simple one for the AC experts, but I'm scratching my head.

I got out of my OBS Ford truck after about a 20 minute drive this evening and noticed that there was a drip coming out of the back of the engine compartment. I popped the hood to find that the accumulator was covered with a heavy layer of condensation. The weird thing was that the AC was off and I haven't turned it on in that rig for weeks. I drove it again about 15 minutes later and I turned the AC on to test it and it blew very cold like normal so it's still working. What gives?
 
Condensation on accumulator indicates liquid boiling away inside. Question is, why?

Liquid moves around the system depending on temperature, collecting in the coolest part. The places with the most space for it are the condenser, the evaporator (less) and the accumulator. If the condenser and evaporator are warm but the accumulator is cool, the liquid will go there, probably over a space of hours. Say you park with the front in sunlight and the windows closed so interior gets hot, accumulator's a bit cooler ...

Then you drive ... cool air goes through both condenser and interior (evaporator), they cool dramatically below the accumulator temp so the liquid there boils away cooling it to the temp of the coolest other part. If high humidity, condensation forms on the outside of the accumulator. .

In effect your truck has a heat pipe system as used on many modern laptops -- heat is moved from here to there by refrigerant in a closed system without mechanical input. Another practical application is charging of a car A/C system by having the engine NOT running, connecting a can of refrigerant to the high pressure side (a NO-NO if running!), icing the accumulator and slightly warming the can (pan of warm water -- never flame) -- look up the safe temperature for the can and stay well below it. This will move the liquid in the can to the accumulator over a fraction of an hour.

One other less cheerful possibility is a leak in your system. But probably not, and in any case you'll know quickly.
 
many people fail to recognize that the compressor runs in other scenarios other than A/C

You must have had window defroster on.

Or a lot of auto climate controls will run the compressor quite a bit unless you intervene.
 
I had the AC and the heater off the whole day. It was pretty mild - mid seventies. Also, it's an old truck without automatic climate controls. The only other detail that comes to mind was that I parked it on a hill all day with the front facing down. I'm curious to see if it does it again.
 
Thanks. The clutch wasn't engaging on the compressor.

I drove the truck to work today and tried to reproduce all the variables, but the accumulator never got cold.
 
How did you figure that out when he didn't mention it? I mean the F150 had a bunch of bodystyles. 1987-91, 1992-96, 1997-03, 2004-08, etc. Any one of those could be the OBS from the next generation.
 
OBS is a Ford thing, I guess, and is understood to refer to the 92-97 generation of trucks. Don't quote me, but I think the term got started when the Super Duty line of heavy duty F250 came out mid year so you could get a "new" or "old" body style truck around '97 and the name eventually stuck on that whole generation of pickups.
 
The new body super duty came in 1999 if I remember correctly. Before then, F150 looked the same as F250 and F350. Like this '95 F250 I had once.

2.jpg
 
atikovi said:
How did you figure that out when he didn't mention it? I mean the F150 had a bunch of bodystyles. 1987-91, 1992-96, 1997-03, 2004-08, etc. Any one of those could be the OBS from the next generation.
Click to expand...
Just because a truck is old and has an "old-looking" body style, doesn't make it an "OBS." OBS is understood to refer to only 92-96 F-Series. The other generations already have other nicknames, e.g. brick nose, bull nose, dent side, bump side, etc.
 
If the compressor has a clutch then it was stuck on for some reason. Just keep an eye on it to see if you can catch it being on when it shouldn't. It's either a mechanical problem with the clutch or an electrical problem where power is turning on to the clutch when it shouldn't be.
 
ripcord said:
Are there any fault modes that can result in the clutch being engaged when the controls are set to the off position?
Click to expand...
not enough clearance in the clutch, shorted clutch power wire to a 12V line, stuck clutch relay, relay control wire shorted to ground, etc.
 
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