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A/C & RPM's


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Old 08-10-2004, 06:40 PM   #1 (permalink)
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Question A/C & RPM's


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I'm not to sure what to do about this and I'm hoping that someone can offer me some sort of explanation before my extended warranty runs out and I'm stuck with a major problem.

My 2000XLT runs like a dream, with one exception.......

I turn the control dials to cold and leave it on floor/panel. Hardly ever do I turn it onto the designated A/C setting, it gets cold enough so never find the need.

After doing stop and go driving throughout the city, every time I pull up to a stoplight, I watch my RPM's bounce up and down and feel the engine pull (don't know if that's the right terminology, but that's what it feels like). But it doesn't do it when I drive straight for 5 -10 minutes without stopping, seems that the stop and go driving is the culprit.

Talked to the dealership where I got it from and some idiot gave me the lame explanation that "its just the way Fords are" I then promptly hung up the phone and am now writing to all of you hoping for more of an educated explanation.

I hope I gave you enough info, but please holler at me if I didn't!

Thanks all! I appreciate it greatly! :)
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Old 08-12-2004, 02:12 AM   #2 (permalink)
 
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So, it doesn't do this when the HVAC controls are in the OFF position?
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Old 08-12-2004, 09:39 AM   #3 (permalink)
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It sounds as if the A/C compressor is cycling off and on during this interval.
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Old 08-12-2004, 03:18 PM   #4 (permalink)
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Paul: thats what I am thinking, and I dont think its suppose to do it!

Monsta: it never does it when its OFF, only when the thermostat is turned all the way to cold and the other knob is in the Panel/Floor position.
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Old 08-12-2004, 04:44 PM   #5 (permalink)
 
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How is the A/C working? What I think is happening is that you have an insufficient amount of freon in your system. There is a Low Pressure switch on the system that will turn the A/C off when it is running - the theory is that this protects the system from sucking in air from a leak point, which will happen on the suction side of the A/C if the freon level gets too low.

I would take it in to a shop and have the system vacuumed out, checked for leaks and refilled. You could also try to the system yourself with a kit you can get from any auto parts store, but unless you are familiar with A/C systems (I had been in a former life an A/C mechanic), I would advise against it since you need some special tools (i.e. gauges), and since new systems do not have a sight glass anymore to help you determine if the system is flash gassing.

Note to all, EVERY auto A/C system leaks, albeit small, from the seal around the shaft on the compressor, so everyone will eventually have to recharge their A/C system. This is just a simple fact for non-hermetically sealed systems (like your home A/C). The trick to keeping the leak at a minimum is to occasionally run the system the keep the shaft seal lubricated.
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Old 08-13-2004, 03:32 AM   #6 (permalink)
 
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Okay, I'll go out on a limb here and say that if she feels the air is getting cold (it should since the AC runs in the face/floor position) then the compressor is running.

I think the problem lies with the fuel delivery (fuel filter old, sticky throtttle linkage or plate etc.) or even the Idle Air Control (that damned! IAC again) unit.

Seems since it doesn't happen when driving after 5-10 minutes of steady state cruise with no varying "stress" on the fuel delivery, then the AC may not be the culprit.

It can, however, be the common denominator!

When the AC compressor runs it tells the PCM to keep the idle up to compensate for the increased load at idle.

The stopping & going of city driving could be causing something "to not return to center" <---- not to be taken literally.

Maybe not enough fuel, or even air, is getting in because the fuel pressures & loads keep changing.

Could also be heat related. It gets hotter under there in town driving.

If it were my truck I would;

1. Replace the fuel filter. (Cheap, easy & required maintenance anyway)

2. Run injector cleaner through a tank. (Good stuff only. I like Chevron Techron.) This actually solved a similar problem with my Dodge Grand Caravan.

3. Verify the correct tension & condition of the drive belt. (takes 2 minutes)

4. Inspect and replace the air filter, if needed.

After doing those simple things, I would report back to youse fellas. :)

I would also like to know at what RPMs does the truck idle between?
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Old 08-13-2004, 07:52 AM   #7 (permalink)
 
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monsta,

Good points...we should all give a quick maintenance history when we post so we know if these items had been attended to recently.

I still am not so sure that it is not the A/C, but there is a quick way to find out. Just let the Expy idle for a while in the driveway and actually look at the A/C unit. You can see/hear if the clutch pulls in and out while running, and if so it probably is the freon level. If not, certainly do as monsta says (actually, if it has not been done yet or for some time, they are all good things to do anyway!)
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Old 08-13-2004, 01:02 PM   #8 (permalink)
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WOW!!!!!! You guys are great!!!

I have been doing some further research on my own, (I am a very stubborn woman!!). Here are some things that I have read/heard:

(You can tell if there is a leak because of the oil residue on the compressor line.) OK, so lifted the hood, found the line and sure enough if it isn't oily and full of dirt/dust/grime. RWinch you said all A/C's leak, will the oil be on the line, all the time?

(Cycling because of lack of Freon) When I took the cap off (where they put the Freon in) it made a "fffsssst" noise, like there was pressure buildup. This was this morning; the truck hadn't been run with the A/C on for 12 hours.

(IAC) if I understand it correctly it is a little switch that keeps the idle in check. Monsta: you mentioned it, can you possibly explain it further?

You can hear the clutch pull when the compressor cycles, don’t need to let it idle in the driveway to answer that one.…..Oh and another thing, its probably totally unrelated, but after I turn the truck off, get out, and listen you can hear the condensation drip off and hit something hot (thinking exhaust). Is there suppose to be that much condensation coming off?

As far as the maintenance issues, I will definitely do the stuff you mentioned this weekend… Again, you guys great. I have been "watching and reading" on the site for 8 months….. finally decided that I needed to actually get involved… Thanks for everything :)
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Last edited by MizzCricket; 08-13-2004 at 01:12 PM.
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Old 08-17-2004, 05:54 PM   #9 (permalink)
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Ok guys... Truck is going in the shop on Thursday to check the Freon levels....................... cross your fingers and toes !!

I'll follow up as soon as I know something :p
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Old 08-17-2004, 11:07 PM   #10 (permalink)
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Answers to a couple of your questions:

The amount of condensation on the A/C components will depend on the humidity. Higher humidity = more condensation. From what I understand, the condensation drain outlet is directly above the exhaust- so that's exactly what you thought!

The IAC is a "bypass valve" of sorts. When you are not pressing on the accelerator, the butterflies in the throttle-body are closed. Thus, no air can enter the engine. Obviously, the engine can't run without some air for combustion. The IAC allows just enough air to 'bypass' the closed throttle-body to keep the engine running at idle.
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