Is A/C somehow connected to the Vacuum pump? - Ford Powerstroke Diesel Forum
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Old 05-25-2012, 09:07 AM
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Is A/C somehow connected to the Vacuum pump?

First a caveat: I am not a mechanic and this is my first diesel no less first powerstroke. It's a 96 F250 crew w/250K on it. I have no idea what the history of the truck was but I have had to replace the front end and the timing cover, of all things.

Now, A/C hasn't been working for a year and I am in Texas and it's damn hot. So I did some research and found it could simply be the harness on top of the compressor and sure enough if I wiggled it just right the clutch would engage and cold air would blow. So now the harness must be makeing contact right because A/C is working but after about 15 minutes of driving my brake and ABS lights come on.

The only other time those lights came on was a bout 6 months ago, they started to come on and about the same time I had the recall done on the harness that goes into the end of the brake fluid/master cyclinder. They went off and never came back on after that. Until now. Now the come one after driving with the A/C on for awhile and only one time, so far, they came on without the A/C having been on but after driving for about 15 - 20 minutes.

So what could be the issue? I heard those lights come on sometimes due to malfunctioning vacuum pump (?). If that thing is about to go out, am I going to die a fiery death due to no brakes/power/etc.?
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Old 06-04-2012, 03:44 PM
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Awesome, you have discovered what the Ford manual affectionately calls the FGT or Ford Giggle Test. Yup, Ford wiring harnesses suck. Only the doors under the dash that you select between windshield (defroster selection), lap, and feet use the vacuum as far as thermal controls go. I've not seen the brake/ABS light thing before but would like to think that the system might be freaking out with the short you have to the A/C compressor. A lot of times the wiring will brake VERY close to the connector and not what it is connecting to.

Do you have a DVOM? Test the wiring on the connector on the A/C compressor to confirm that it is the harness and not the compressor. If it is the harness then pop over to a Pick-A-Part and cut one off another truck and solder into your harness.

Good Luck!
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Old 06-04-2012, 06:36 PM
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That's what I am hoping, BigFuel. It was just too coincidental that the lights started coming on AFTER I wiggled the A/C harness. And the wires were bent very tightly right at the harness connector into the compressor.

One edit to my previous comment though, the lights have come on a couple of times during a drive without me ever turning on the A/C. Usually about 20 - 30 minutes into a drive. These are usually stop and go drives ... this is my daily driver.

If there isn't any connection to the lights coming on and the A/C working again, and this is signaling a vacuum system failure, what should I look out for/feeling in the truck? Will the brakes go out or just get harder to press?

ALso, I don't have a DVOM but would any ol' multimeter work? What am I looking for with the DVOM?
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Old 06-05-2012, 12:21 PM
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Any multimeter will work, it's just not common anymore for someone to know how a analog meter works. Disconnect the harness and on the compressor first make sure that the male contacts are not broken or susceptible to movement. They should be very ridged otherwise the contacts are broken just inside the compressor. Set the meter to Ohm, cross the probes to make sure that the meter is working (should see a sweep from infinite or OFL to 0 if analog or .1 if digital), if analog turn the calibration knob till it reads as close to zero as you can get it without going past it (I'm not trying to be an ***, I don't know how much experience you have with a multimeter and if this is useful to you then it will save a post-back). Touch both contacts and take a reading.

If the number is very low then take one of the leads and touch the compressor housing and then the pulley. If it reads infinite to the housing and pulley but low to the both contacts then the electromagnet is good and not shorting.

The harness is a little harder as I think that the female holes are smaller then the meter's lead's tips. In this case get some wire or a paperclip and carefully insert them into the harness plug take your reading (might have to turn the A/C on) with the meter's setting on VDC. While taking the reading flex the wiring and see if the positive signal comes and goes. The "open" is probably going to show here. Also, usually, the brake is so close to the connector that it is easier to cut a working one off a wrecked truck then to try and fix the one you have. It doesn't even have to be the same truck it just has to be the same connector.
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Old 06-05-2012, 12:55 PM
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BigFuel, I didn't take your comments as being condescending or the like. In fact, your answer has the detail my dumb @ss needs to learn this stuff. This is very helpful and I'll see what I can do with it. Atleast it gives me an excuse to go muy a digital multimeter.
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Old 06-05-2012, 12:56 PM
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Quote:
Originally Posted by xbrotherx View Post
One edit to my previous comment though, the lights have come on a couple of times during a drive without me ever turning on the A/C. Usually about 20 - 30 minutes into a drive. These are usually stop and go drives ... this is my daily driver.

If there isn't any connection to the lights coming on and the A/C working again, and this is signaling a vacuum system failure, what should I look out for/feeling in the truck? Will the brakes go out or just get harder to press?
When was the last time the brake fluid was flushed? Every three years for a new system. As frequent as every year for a really worn system. New fluid is near clear, old is very dark and will probably have stuff floating in it.

Hit your local parts shop and borrow a vacuum gauge (usually free). Carefully (might be old rubber) disconnect the vacuum line from the brake booster. Start truck and take a reading off the hose. In optimum shape your looking at around 20" of mercury. Worn pump or bad rubber hoses will be a much lower reading, like 6" of mercury. If the reading are good use the vacuum pump and gauge on the brake booster. After pumping it down watch the gauge for a very slow return to 0. If the system stays in vacuum then the one way valve is good. If it'll slowly return to 0 then the Diafram is good but the one way valve is bad. If you cannot get the booster to take vacuum then your booster diafram is bad. The vacuum pump, little pulley under the A/C compressor, usually starts squeaking (bad bearings) or pops (bad diafram internally) before it fails.

Bad fluid holds water in solution which would cause rusting and internal damage to the moving parts (ABS system, master cylinder primary and slave piston seals, internals of the calipers and drum cylinders).

Bad vacuum will cause VERY hard braking but the system is still intact on the hydraulic side.

Last edited by BigFuel; 06-05-2012 at 01:01 PM.
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Old 06-05-2012, 01:12 PM
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Originally Posted by BigFuel View Post
When was the last time the brake fluid was flushed? Every three years for a new system. As frequent as every year for a really worn system. New fluid is near clear, old is very dark and will probably have stuff floating in it.
Since I've had it, I have not flushed it. And I've had it a year so I should probably get it flushed since who the heck knows when the last time was. Not sure about the color of the fluid ... never looked (good mechanic I am, huh).

I have heard a rhythmical squeak when was cold outside and the truck was warming up. It was a rhythm like a quick 1 .. 2 .. 3, then a pause then it repeated and I heard it over on that side. With my luck the pump is going out but your instructions are detailed enough to get me started on diagnosing the issue at least.

Worst case, how much do vacuum pumps run to get and put in if I had someone else put it in? If it's not too difficult I could possibly do the work myself. Understand the only mechanical work I have done myself on my truck is put in a new starter and change the oil. Woo hoo.

Last edited by xbrotherx; 06-05-2012 at 01:17 PM.
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Old 06-05-2012, 01:55 PM
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Mine squeaked for several minutes or so when cold and became persistent before failure. My business went under last year and I didn't have a real job for at least year as I hoped it would last till I had some good money to swap it out. I pushed it too long and the bearing failure took out my belt, loosing power steering and braking. Amazing how much the power assist really does assist! Was able to get it to the side of the road without any damage, just scary and I'm glad that my wife wasn't driving it at the time.

Doing the flush yourself is not hard you just need two people. One to pump up the brakes and the other to bleed the system. Just the same as a bleeding the brakes after some work. Start at the farthest wheel in the system (passenger rear) and go at it till the fluid coming out is the clean fluid that went in. Constantly check and refill the brake reservoir so that new air doesn't get into the master cylinder working your way to the driver rear, passenger front, and finally driver front. It doesn't have to be tight but DO keep the lid on the reservoir as brake fluid squirts about and it'll take your paint off. DO NOT let the pedal go past half way down as this will cut the wiper seals on the inside if you go to far. Done. While we are doing a PMC get a couple gallons of power steering fluid, funnel about 12" long, and a somewhat narrow turkey baster that will fit into your power steering pump/tank. Lift and block the front of the truck so that the front tires are not on the ground. Block the rears. Start the truck and be VERY careful with the next couple steps as the trucks cooling fan is now spinning:

-Cover the BOTH of the trucks batteries with a non conducting matierial (wood or thick cloth)
-remove the power steering resevoir cap and set out of the way
-use the turkey baster and remove some fluid from the resevoir (not too much as this will allow air into the pump, the baster will hit a "metel thing" straight in from the top if you just probe in. That's the pump. Keep the fluid above this)
-use the narrow funnel to pour in some new fluid (this is where the longer funnel shines as it keeps your pour out of the wind from the fan)
-turn the wheels left and right
-repeat till the fluid comming out is about the same color going in (you wont get all the old fluid out but you did just get most of it out without exposing the system to air

-top tank to the fill line on the dipstick/cap. Done

Vacuum pump prices very by brand. $100 for real cheepies to $250 for stock replacement. Easy to replace yourself. Remove belt, three bolts hold it to the block, disconnect rubber hose, take to parts store as (this is the only "hard part" but a lot of shops will do this for you) you MUST use a pulley remover and installer to move the pulley to the new pump and to the same depth as the old one. Prying it off the old one will bend it and "tapping" it onto the new one will push the rotational shaft out of alignment of it's internal parts.

Last edited by BigFuel; 06-05-2012 at 02:14 PM.
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Old 06-05-2012, 02:13 PM
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BigFuel, you have been very generous with your time and knowledge helping me out here! Thank you. I will do these diagnostics and see what I come up with.

A confession for ya here, I was not very smart in buying my truck. I saw the pictures and description on craigslist, drove an hour and half to look at it, was blinded by the fact that it had EVERYTHING I wanted including be year and bought it. Did all this not knowing that the front end was shot, the timing cover had a crack, etc. etc. Hell, even the 4-wheel drive stick was not there but the dude selling it had one loose in the truck and said it just needed to be put on.

SO I have dropped cash on all new ball joints, tie-rods, etc. A new timing cover which required pulling the engine out (not me the mechanic and maybe I got bamboozled on that one too), I put the new starter on, the clearance lights were never wired in ... just decorations so I wired those up, gotta fuel leak in the valley somewhere and who knows what else.

That's my sermon and I'm stickin' to it.
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Old 06-05-2012, 02:24 PM
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No worries friend, I went from private mechanic on my uncles rigs, to a dealership mechanic (Ford and Toyota), to heavy industry mechanic (heehee BIG toys), to custom vehicle builder (my own shop that is just kinda coming back in sales with people starting to spend money again), to now teaching this stuff at California State Polytechnic University Pomona. I'll take them young and old and show/help them with anything they want bumper to bumper. Knowledge is meant to be passed. Hit me if you want to know more about the fuel leak but there are several treads on that as well

Good luck with your rig,
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