Air conditioner questions

[MagikDraggin]

First question:
By what mecnanism does the A/C system (not the auto-air) cause the fans to push less air ...or is it that the fan actually slows down, when the suction line and the evaporator ices up?

Second question:
Is the action of the A/C system controlled by the main computer that runs the engine, timing and emissions controls, or is there some other "brain" that runs just the air conditioner?

Third question:
How are the 4 speeds determined for the fan? Is it by way of resisters on the selector switch itself or are there actually 4 windings in the fan motor? Or something else?

 

[jmccloud]

A/C Questions

I'm not sure I've got the answers to the correct questions. If these replies miss, please be patient and ask again.

The fan push buttons control the fan speed via two relays (hi and lo) and three resistors, essentially bypassing the computer (on a manual A/C). The resistor (actually three resistors in a pack) are located in the evaporator coil housing in the engine compartment. The relays are just behind the right front wheel house. There are several other relays there, I can look up which is which if you need.
If the evaporator (cold coil in the dash) freezes up, that will restrict the air flow but not slow down the blower speed. It's not supposed to freeze up.
The 4 buttons for A/C (recirc, a/c, bilevel, and defrost) are wired to an 'OR' circuit in the control head (what you see in the dash). This circuit grounds a transistor lead to the computer that indicates to the computer that you want A/C.
The A/C compressor responds to the computer via a compressor clutch relay. That relay is also controlled by the freon low pressure switch and hi pressure switch. Either switch can open the magnetic clutch via the relay.
On modestly warm days, the compressor will pull the low pressure down because the evaporator (cold coil in the dash) can't evaporate enough freon to keep the compressor supplied. Then the low pressure switch opens the relay and the relay opens the clutch. After the pressure builds (due to cockpit air heating the evaporator), the low pressure switch closes, closes the relay and engages the compressor magnetic clutch.
The temperature control slider opens a door to the heater core, thereby adding hot air to the evaporator outlet air. This temperature control slider has nothing to do with compressor cycling.
On Hot Hot Hot days, the evaporator heats the freon enough to keep the compressor busy.
The high pressure switch is for safety (clogged condenser, defective engine coolant fan, etc.) and doesn't typically do any control.
Hope this helps

 

[FordNoMore!]

And Im a AC tech, not auto , but HVACR, and JMC is quite correct,Good Points

 

[MagikDraggin]

Re: A/C Questions

I'm not sure I've got the answers to the correct questions. If these replies miss, please be patient and ask again.

You answered the questions very well indeed. At least I have a better understanding of how the system works. Still, I haven't been able to solve the problem.

Even on the hottest (and especially on the hottest) days, I have noticed that the suction line, from the accumulator (the cylindrical can by the radiator fans), to the box immediately beneath the radiator overflow, will not simply become frosted, but will completely get ice covered. This, in turn, causes a severe reduction on air flow out of the dash vents.

So far, it would seem, if I start the unit off with the fans on high and do not touch any other buttons, it works just fine......but if I chose another button in order to have the air come out of the floor vents as well as the dash vents, or mess with the fan speed selector buttons after it has been running for awhile, the quantity of air coming out of the vents is severely reduced and the interior becomes quite uncomfortable.

Only shutting off the motor and A/C completely for about 10-15 minutes, allows everything to work normally again.

I don't have any gauges or any real expertice on automotive a/c systems, so I am not inclined to attempt any repairs myself, however, I WOULD like to have some idea of what the problem could possibly be, so as when I do take it in to the service techs, I won't be completely at their mercy and be talked into paying for services that I may not necessarily need.

 

[MagikDraggin]

UPDATE.

Ok, had the vette out today for a drive in the country. It is NOT the fans that are slowing down, (as I had previously suspected), it is the diverter doors that are not staying open, therefore are restricting, if not blocking, the air from coming out the dash vents.

Now I inspected the vacuum line and the fittings that appear to feed these doors (part of it is teed off from a line that runs beneath the passenger side fuel rail cover) and all seems to be in ok shape.

Is there something I can check as to the possible cause of this.....is it a drop in vacuum, or something else that prevents the door(s) that allow air to come out the dash vents from opening.....I get sufficient air out the floor vents.

Any ideas?

 

[jmccloud]

Air vent control

There are several threads on this but they at first appear to be on a different subject; that is the 'A/C Programmer'
It's located generally above the gas pedal and is difficult to see much less reach and service. There's a vacuum distribution block that is infamous for leaking. The failure/default mode is to direct the air out the defroster vents and the floor vents. If your air is coming out those two places in lieu of the A/C vents, the distribution block on the A/C programmer is the place to look. Yes, this is for the manual A/C too.
There's a push-on nut that holds the distribution manifold in place. The talk on the treads indicates the post this nut fits onto is fragile and often breaks during service attempts. It looks like there are 5 or 7 vacuum lines, one of which is the source.
I've never been into this thing and would suggest you use the 'Search' menu above to find the appropriate threads. Key words of vacuum connector, a/c programmer, wrong vents, etc. should turn something up.
Hope this helps
PS If the air is NOT coming out the defroster and floor vents (but is simply reduced in quantity), your evaporator may be freezing up due to inappropriate charge (too much?? or too little??) Check this out early in the diagnosis as the A/C programmer connector appears to be a bear to service.