Subject: 05 F250SDCCLB4x4, 34K miles.

Got home from work yesterday and noticed fluid dripping near the front right wheel. I felt it and it wasn't oily nor did it smell. I tasted it and it wasn't sweet, so, ... , straight water?

A/C Condensate!

I used the exclamation point because the HVAC control was on the "face+foot" position, the first click right of OFF. By virtue of no reference to A/C operation in this position (no "A/C" markings nor defrost symbol, both indicative of A/C compressor operation), I was under the assumption that the A/C should NOT be on in this case. I popped the hood and sure 'nuff, the A/C lines were cold up by the blower motor, and the two lines to/from the condensor were hot/cold. I had noticed some "A/C operation-like noises" when idling over the last few days of running the truck w/ the HVAC control in this position, which made me a bit suspicious. This confirmed A/C operation. WTF?

I had read where vacuum leaks near the front auto hubs may manifest itself as weird HVAC operation, apparently needing vacuum to direct air to places other than defrost/windshield, i.e. strong vacuum leaks will lead to air going to the windshield, regardless of the control position. I did note a cracked vacuum hose last weekend when doing a tire rotation, so I taped it up pretty good (I have intentions of blocking it off altogether and have manual hub operation only). I indeed get airflow switching when cycling the HVAC control through its 8 or so positions, so I was thinking that there wasn't a substantial vacuum leak.

I don't think that the A/C compressor clutch is always engaged, as I can hear the clutch engaging and disengaging too (e.g. at the foot-only and face-only positions there's no clutch engagement, but there is engagement/engine tone change at defrost, defrost+foot, A/C, Max A/C, and the aforementioned face+foot, so I don't think that hypothetically there's a compressor clutch relay that's stuck "on".

Is fac+foot supposed to engage the A/C clutch?

Thanks in advance for any tips the collective may be able to provide.

Mark

 

The clutch will cycle (engage every so often for a few moments) to keep the system fluids circulating, even when the AC is not turned on. This is normal.

The water you see dripping is condensation on the AC system. That is also normal.

 

I did another coupla test drives since that event (3 actually). In one case, I kept the control at OFF and there appeared to be no clutch engagement at all and at the culmination of that drive, both A/C lines in the engine compartment were similar, warm temperature. In another test, I kept the control at the face-only position (one click to the left of OFF), where I though that there wasn't any engagement that I could detect and again, indeed, a quick hand-check of the A/C lines indicated no engagement at that position either.

Is this "random A/C operation in order to keep things well-lubed and lines dry, etc." function supposed to be at ALL HVAC control positions? In my case, it appears to be only in that face+foot (in addition to the obvious ones).

Mark

 

The only two positions where the AC compressor clutch is always off is "off" and "vent" (the first click to the left) as you noticed.
In all the other positions, depending on the temperature control setting the compressor can come on. I have put a switch inline so that I can run hi/lo vents or defrost without the
AC.

 

SCHWING!!!!!!!!

Yeah, that's exactly what I was thinking of. In some other cars (some Japanese, BMW), there's a manual control for A/C clutch operation, and I like that. A lot. I really am NOT a fan of letting some "system" determine when to do it. I like having the control (not surprisingly, I drive a manual transmission, but I digress).

Might you happen to have a schematic of how you incorporated your A/C clutch switch?

Mark

 

I researched this a little further (farther?), and can now answer my own question. From a saved copy of a Workshop Manual that I found somewhere on the Internet (granted, it's for an '06, but I gotta figure that my '05 is gonna be pretty close), I found this:

System Airflow Description — Manual Climate Control
Max A/C
When MAX A/C is selected:

• The air inlet door vacuum control motor is at full vacuum, closing off outside air and admitting only recirculated air.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at no vacuum position, directing airflow to the instrument panel A/C registers.
• The heater control valve (if equipped) is at full vacuum, preventing the flow of hot coolant to the heater core. Blended air temperature is not available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F).
• The blower motor is on.

A/C
When A/C is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at no vacuum position, directing airflow to the instrument panel A/C registers.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F).
• The blower motor is on.

PANEL
When PANEL is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at no vacuum, directing airflow to the instrument panel A/C registers.
• The temperature can be adjusted to heat the air but the air cannot be cooled below the outside temperature.
• The A/C compressor will not operate.
• The blower motor is on.

OFF
When OFF is selected:

• The air inlet door vacuum control motor is at full vacuum, closing off outside air from entering the passenger compartment.
• The panel/floor door vacuum control motor is at full vacuum and the panel/defrost door vacuum control motor is at full vacuum, closing off airflow to the defrost duct, side window demisters and instrument panel A/C registers.
• The A/C compressor will not operate.
• The blower motor is off.
• The coolant control valve (if equipped) is at full vacuum, preventing the flow of warm coolant to the heater core.

PANEL/FLOOR
When PANEL/FLOOR is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at full vacuum and the panel/floor door vacuum control motor is at partial vacuum, directing airflow to the instrument panel A/C registers and floor duct.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F).
• The blower motor is on.

FLOOR
When FLOOR is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/floor door vacuum control motor is at full vacuum and the panel/defrost door vacuum control motor is at no vacuum, directing airflow to the floor duct.
• The temperature can be adjusted to heat the air, but the air cannot be cooled below the outside temperature.
• The A/C compressor will not operate.
• The blower motor is on.

FLOOR/DEFROST
When FLOOR/DEFROST is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door vacuum control motor is at no vacuum and the panel/floor door vacuum control motor is at partial vacuum, directing airflow to the defroster duct, side window demisters and floor duct.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F).
• The blower motor is on.

DEFROST
When DEFROST is selected:

• The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
• The panel/defrost door and panel/floor door vacuum control motors are at no vacuum, directing airflow to the defroster duct and side window demisters.
• Blended air temperature is available.
• The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F).
• The blower motor is on.

So the A/C is on in every position other than "Vent" (panel only, 1 click left of OFF) and Floor-Only. Otherwise, the A/C will be in operation if ambient temperatures are above approximately 43 degrees F. I learned something today. Cool.

Mark

 

One of my future mods is an AC clutch cut out switch.