2000 XLT A/C works great! All the time?!?!

[Winger]

Hi all

Recently got my hands on a terrific truck. Ex-FD vehicle in great shape for 127k. No rust and doesn't need much beyond exhaust manifolds, rear seals- the usual.

The intermediate owner Had a grand old time ripping out the FD wiring and almost successfully adding anti-theft. In short the the electrical side is ugly in places.

Anyway, I was less than happy with the 5.4's mpg like most folks. The Gotts mod and a K&M filter seemed to get me from 10 to 12 mpg overall, but that's still pretty unimpressive.

Well we finally had a hot day today and I found something odd about the AC. It works great- All the time! Nothing I do with the controls seem to shut down the compressor.

I bet this does great things for my mpg and the AC compressor Anyone else have a similar experience?

Thanks in advance for any ideas

Winger

 

[stamp11127]

Does the mode selector switch work correctly?

 

[Winger]

Thanks and good morning! It seems to redirect air flow properly, yes. (Not clear why there is an "off" option on it though. Maybe I will RTFM...)

Wherever the airflow is directed, and at any blower speed, the air come through AC cold unless I set the temp dial to hotter right half of the range. But nothing seems to disengage the compressor.

I think I may pull the AC fuse later just to hear what the difference sounds like. I would think a bad relay would fail open not closed, so I suspect something got bypassed. I dudnt find anything in the forum search, but i may not have looked correctly.

Just figured I'd ask around first to see if this is something familiar before I start tracing wiring. Cause I just can't WAIT to open that can o worms...

 

[stamp11127]

Most basic systems run power through mode/function selector, low side switch, high side switch, a/c clutch then ground. I'd check for power at the low side connector with the mode switch off. If you have power the switch is bad or has been bypassed.
The blower has a relay and is on a separate circuit. They can fail open or closed, but this isn't your problem.
The off setting kills power to the blower and compressor.

 

[Winger]

Well, after wasting time looking for a wiring problem, I actually did the forbidden act: I read the owners manual.

Just for context, my last ford was a 68 bronco and I loved it. Since then I've driven mostly foreign cars, so I'm used to a certain design philosophy.

The bottom line is: the Expy AC system is designed to run a whole lot more than I can see any reason for. The controls are NOT obvious in this regard, so as a public service I am posting the relevant owners manual text below.

In short, this is a weird design and I bet significant MPG improvements are possible by paying close attention to these control settings.

Thanks for the tips, stamp. Sorry to waste your time.

Controls and features
The air conditioning compressor will operate in all modes except PANEL and FLOOR. However, the air conditioning will only function if the outside temperature is about 10°C (50°F) or higher.
Since the air conditioner removes considerable moisture from the air during operation, it is normal if clear water drips on the ground under the air conditioner drain while the system is working and even after you have stopped the vehicle.

• MAX A/C-Uses recirculated air to cool the vehicle. MAX A/C is noisier than A/C but more economical and will cool the inside of the vehicle faster. Airflow will be from the instrument panel registers. This mode can also be used to prevent undesirable odors from entering the vehicle.
• A/C-Uses outside air to cool the vehicle. It is quieter than MAX A/C but not as economical. Airflow will be from the instrument panel registers. Air conditioning and heating capabilities are provided in this mode.
• PANEL -Distributes outside air through the instrument panel registers. However, the air will not be cooled below the outside temperature because the air conditioning does not operate in this mode.
• OFF-Outside air is shut out and the fan will not operate. For short periods of time only, use this mode to prevent undesirable odors from entering the vehicle.
• PANEL & FLOOR - Distributes outside air through the instrument panel registers and the floor ducts. Heating and air conditioning capabilities are provided in this mode. For added customer comfort, when the temperature control knob is anywhere in between the full hot and full cold positions, the air distributed through the floor ducts will be slightly warmer than the air sent to the instrument panel registers.
• FLOOR -Allows for maximum heating by distributing outside air through the floor ducts. However, the air will not be cooled below the outside temperature because the air conditioning does not operate in this mode.
• FLR & DEF-Distributes outside air through the windshield defroster ducts and the floor ducts. Heating and air conditioning capabilities are provided in this mode. For added customer comfort, the air distributed through the floor ducts will be slightly warmer than the air sent to the windshield defroster ducts. If the temperature is about 10°C (50°F) or higher, the air conditioner will automatically dehumidify the air to reduce fogging.
• DEF -Distributes outside air through the windshield defroster ducts. It can be used to clear ice or fog from the windshield. If the temperature is about 10°C (50°F) or higher, the air conditioner will automatically dehumidify the air to reduce fogging.

To aide in defogging and demisting (removing condensation on the inside of the windshield) in cool weather:
1. Select PANEL & FLOOR
2. Set the temperature control to full heat
3. Select A/C
4. Set the fan speed to HI
5. Direct the outer panel vents towards to side windows
To increase airflow to the outer panel vents, close the central panel vents.

Operating tips
• In humid weather, select DEF before driving. This will reduce fogging on your windshield. After a few minutes, select any desired position.
• To reduce humidity buildup inside the vehicle, don’t drive with the climate control system in the OFF or MAX A/C position.
• Don’t put objects under the front seat that will interfere with the airflow to the back seats.
• Remove any snow, ice or leaves from the air intake area (at the bottom of the windshield under the hood).

 

[98EXPY 5-0]

To my knowledge, the AC should only function when you are on AC or MAX AC, and it also blips the compressor for a couple seconds while in DEF to pull the moisture from the air, otherwise on a cold day, blowing heat on the windshield would cause condensation to form on the inside of the glass. Are you saying that yours does not function like this? If you have the dial on PANEL, FLOOR or a COMBO setting, the AC isn't on, regardless of the position of the RED/BLUE dial.

 

[Winger]

Well, that's what assumed too, 5-0. That the AC compressor would only engage when the selector was pointed to AC or Max AC. But mine operates just the way the manual I quoted describes above. The AC compressor is only offline when I select Panel, Off, or Floor.

There is supposedly an exterior temp sensor that keeps the AC off below 50 degrees or so. Wonder if that still works...

It's just odd. It must impact MPG. I'm currently running a normal workweek with the AC confirmed off. I'll post how things go after my next fill up.

 

[Winger]

Well, after a week of use with the AC confirmed off, I seem to have some improvement. Went from 12 to 14 mpg, but my mix of city/highway changes a fair amount week to week, so I will test this idea for a few more weeks to see if my overall mpg is consistently better.