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  #1  
Old 08-23-2017, 10:07 AM
Harbor_Handed Harbor_Handed is offline
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Default New IAC Valve but inconsistent idle RPMs

Hi,

I am having some problems with my truck.

A month or so I replaced my IAC valve with a new Motorcraft one from RockAuto because I had noticed some up and down fluctuation in my idle RPMs. Before this, I had cleaned the original IAC valve twice with carb cleaner which seemed to help the intermittent fluctuating, but I finally bit the bullet and just put a new one in.

Well today when I was driving, I noticed that my AC compressor clutch was cycling too frequently: I could hear it engaging ever 2-3 seconds, so I felt it was likely that my AC pressure was low and was needing another recharge (I recharged it back in May...apparently I have a leak). Then I noticed that when I'd come to a stop, the RPMs would rest around 700 RPM, which is not normal. 900 RPM is normal for my truck. Sometimes when I'd stop, it'd be normal at 900 but other times it would rest much lower than normal.

When I got to my destination, I put the truck in Park and popped the hood, and my AC compressor clutch was not even coming on at all, although the AC setting was on with fan on low. I looked at the tachometer and the RPMs were still low while idling in Park although AC compressor clutch was not working.

When I got back in my vehicle a while later and left, I turned the AC off with just the fan on, and I was STILL experiencing the low idling RPMs, sometimes it would drop really low to around 600 before resting at 700 or 800. This is not normal, my truck should be idling at around 900.

Can anyone tell me what is going on? I'm scared my idle will drop further and stall. I don't understand why this is happening. I stopped and bought another AC recharge canister on the way home, and I'll recharge it this evening when it's cooler out. Could the low AC pressure be responsible for the inconsistent idle RPMs - even when the AC is switched off?

Any help is appreciated. Thanks.
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  #2  
Old 08-23-2017, 03:33 PM
Harbor_Handed Harbor_Handed is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

So I recharged my AC and the idle RPMs seem back to normal now. From googling, it seems like other people have noticed the same issue that their idle RPMs get lower when their AC compressor clutch starts clicking a lot, so I guess it's just a normal symptom that it needs a recharge. I was taken aback by it though because I don't think it did that last time I needed a recharge.

Anyway, I hope it stays working fine as long as the AC is pressurize properly.
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Old 08-23-2017, 08:11 PM
spry85 spry85 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Was your A/C still cold when this was happening? My truck is doing this same thing but my A/C is extremely cold which makes me feel like it's not an A/C for mine


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  #4  
Old 08-24-2017, 06:11 AM
Harbor_Handed Harbor_Handed is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Quote:
Originally Posted by spry85 View Post
Was your A/C still cold when this was happening? My truck is doing this same thing but my A/C is extremely cold which makes me feel like it's not an A/C for mine
Yes, my AC was still blowing quite cold yesterday (when the compressor was actually engaging).

My understanding now is that in a properly charged AC system, the compressor clutch stays running all the time and does not click on and off. If your AC compressor clutch is clicking on & off, then that means your AC pressure is getting low. If it clicks about every 6 seconds, then that means it's just starting to get low. If it clicks every 2 seconds then it's very low and is going to fail immanently. So if you're AC compressor clutch is clicking on and off at all, then your AC has a pressure problem and that could be the issue with your idle RPMs (as it was with mine).

If your AC compressor clutch is NOT clicking, then it could just be your IAC valve is gunked up with carbon and needs to be cleaned with carb cleaner or replaced.

Or it could be both of those issues - AC has a leak & needs recharge and IAC valve needs cleaning/replacement.
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Last edited by Harbor_Handed; 08-24-2017 at 06:13 AM.
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  #5  
Old 08-24-2017, 06:16 AM
spry85 spry85 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Thanks for the insight, my AC clicks about every 4-5 seconds at idle. I guess I'll have to invest in some gauges to see what the pressure is at.


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  #6  
Old 08-24-2017, 06:33 AM
Harbor_Handed Harbor_Handed is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Quote:
Originally Posted by spry85 View Post
Thanks for the insight, my AC clicks about every 4-5 seconds at idle. I guess I'll have to invest in some gauges to see what the pressure is at.


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My recharge canister came with a detachable/reusable gauge on it, which is used to test the pressure.

Just remember that the pressure you're looking at is when the clutch engages. When the clutch is not spinning, the pressure on the gauge rises (at least on mine) but when the clutch would start spinning it would fall to almost 0.
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Old 08-24-2017, 06:37 AM
spry85 spry85 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Gotcha thanks, what recharge canister do you have?


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  #8  
Old 08-24-2017, 07:11 AM
Harbor_Handed Harbor_Handed is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

I use Arctic Freeze, it's like $35, and in the future you can just buy the cheaper canister without the gauge on it because you reuse the gauge on this one.

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  #9  
Old 08-24-2017, 07:13 AM
spry85 spry85 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs




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  #10  
Old 08-24-2017, 06:21 PM
GSF1200S GSF1200S is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

FWIW, I really recommend going ahead and picking up a set of gauges and the adapter for refrigerant.

The bottles with the gauges are fine I guess, but it only gives you half the story and isn't anywhere near as useful to t/s air-conditioning problems as a full set of gauges.

A full set of gauges can show you blockages, compressor problems, whether low or high pressure is kicking off the A/C, etc.

Another problem with some of those gauge type bottles is that the refrigerant often contains stop leak. Stop leak will make A/C work in the future miserable for whoever does it, and likely wont fix the leak at all.

The best thing to use is the cheapest R134a refrigerant you can find that has no stop leak at all. At most, use some that has UV dye so you can use a UV light to find your A/C leak.

And really, it depends on the leak as to whether you should fix it. If a hose or fitting has a small leak that takes a year to require a recharge, the hundreds of dollars you'd have to spend to evac the system, replace the hose, vac the system, and recharge the system (assuming this is done by shop) would be 10-15 times more expensive than just recharging the system with a cheap can of R134a. And thats not even getting into the folks who believe that the accumulator should be replaced every time the system is opened up, etc..
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  #11  
Old 08-25-2017, 04:11 AM
tomw0 tomw0 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Harbor:Just remember that the pressure you're looking at is when the clutch engages. When the clutch is not spinning, the pressure on the gauge rises (at least on mine) but when the clutch would start spinning it would fall to almost 0.

ZERO!! Not good. Too low. The clutch should have released before it got that low.

Two things: The refrigerant was already boiled away, so no extra cooling from going so low. The refrigerant carries the lube to the compressor. No flow == no lube. Bad for the compressor longevity.
R134 will boil at low pressures, and create low temperatures as it boils. If you lower the pressure much below the mid-20's, you'll get frost formed on the evaporator. Get enough frost, and the air won't flow by. Nice ice cube you got there, bud, though it won't cool your cab.
You should have your LPCO switch checked. (Low Pressure Cut Out.) It is there to prevent frost and lube-less compressor.
I suspect you may have a restriction. How long does the pressure take to bleed off after you shut down the A/C & engine? Compressed refrigerant that is already on its way to the evaporator will flow past the restriction(TXV / FOT) and do its thing, evaporating in the evaporator, and will/may make noise. It should 'equalize' the system pressure pretty rapidly after shutdown. If it take time, like over a few minutes, it may be restricted. How well does it cool when functioning?
tom
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Old 08-25-2017, 05:53 AM
Harbor_Handed Harbor_Handed is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Quote:
Originally Posted by tomw0 View Post
Harbor:Just remember that the pressure you're looking at is when the clutch engages. When the clutch is not spinning, the pressure on the gauge rises (at least on mine) but when the clutch would start spinning it would fall to almost 0.

ZERO!! Not good. Too low. The clutch should have released before it got that low.

Two things: The refrigerant was already boiled away, so no extra cooling from going so low. The refrigerant carries the lube to the compressor. No flow == no lube. Bad for the compressor longevity.
R134 will boil at low pressures, and create low temperatures as it boils. If you lower the pressure much below the mid-20's, you'll get frost formed on the evaporator. Get enough frost, and the air won't flow by. Nice ice cube you got there, bud, though it won't cool your cab.
You should have your LPCO switch checked. (Low Pressure Cut Out.) It is there to prevent frost and lube-less compressor.
I suspect you may have a restriction. How long does the pressure take to bleed off after you shut down the A/C & engine? Compressed refrigerant that is already on its way to the evaporator will flow past the restriction(TXV / FOT) and do its thing, evaporating in the evaporator, and will/may make noise. It should 'equalize' the system pressure pretty rapidly after shutdown. If it take time, like over a few minutes, it may be restricted. How well does it cool when functioning?
tom
Thanks.
I think I misspoke, when I wrote it would fall to almost zero I just meant that when the compressor clutch engaged it would rapidly start falling into the low range, but then the clutch would disengage and the pressure gauge would start climbing again. It did not get to zero, and I honestly don't remember precisely where it would fall to before the clutch disengaged and it started climbing again, but it did start falling rapidly which made me think if it continued to fall it would go way down to around zero.

My AC was nice and cool before it started malfunctioning. And after recharging it a couple days ago it blows colder than ever. I've never noticed any frost, it just condenses a lot of water.

When I shut the truck down with AC on, I could generally hear it hissing under there for maybe 4 seconds or so.
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  #13  
Old 09-15-2017, 04:45 PM
spry85 spry85 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

So I got my system looked at and found a leak at the evaporator but the level wasn't very low, got it serviced back up and the compressor stills clicks on and off like before while at a stop. The guys at firestone said they checked all the pressure switches and the recommend replacing the evaporator because of the leak and replace the condenser because of the clutch engaging and disengaging all the time. Any thoughts?


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  #14  
Old 09-16-2017, 05:13 AM
tomw0 tomw0 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Quote:"and the compressor stills clicks on and off like before while at a stop."

Your techs said:"they checked all the pressure switches and the recommend replacing the evaporator because of the leak and replace the condenser because of the clutch engaging and disengaging all the time."

Their suggestions make no sense unless they had boat payments or orthodontist bills coming due real soon.
If the leak is small, as in will last the season, the replacement cost(labor & parts) could be significant as the system needs evacuation, and the complete dashboard has to be R&R'd. A full day's work. THEN the system vacuumed and refilled.
The condenser has about as much with the clutch action as my left elbow. Unless high head pressures are developing due to a condenser that is blocked, and cannot pass air over the fins, or is blocked internally, it should work. There are no moving parts.
Before doing any of the above, I'd want to see at rest pressure and ambient temperature, running pressure & ambient temp, HI & LO, and center outlet temp. I'd also want to see the pressure readings when the clutch releases, and when it re-engages.
Cycling can be due to 1)high head pressure - HPCO, 2)low evaporator pressure - LPCO, or 3) weak clutch, 4)too much/little gap, 5)clutch power problems such as bad brushes or corroded terminals or broken feed wires. Which do they suggest you have causing the cycling? A condenser can cause cycling only if head pressure rises due to blockage, and you reported COLD air, which you won't get with blockage. I'd like to hear that explanation as it makes no sense from my point of view.
tom
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Old 09-16-2017, 06:49 AM
spry85 spry85 is offline
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Default Re: New IAC Valve but inconsistent idle RPMs

Quote:
Originally Posted by tomw0 View Post
Quote:"and the compressor stills clicks on and off like before while at a stop."



Your techs said:"they checked all the pressure switches and the recommend replacing the evaporator because of the leak and replace the condenser because of the clutch engaging and disengaging all the time."



Their suggestions make no sense unless they had boat payments or orthodontist bills coming due real soon.

If the leak is small, as in will last the season, the replacement cost(labor & parts) could be significant as the system needs evacuation, and the complete dashboard has to be R&R'd. A full day's work. THEN the system vacuumed and refilled.

The condenser has about as much with the clutch action as my left elbow. Unless high head pressures are developing due to a condenser that is blocked, and cannot pass air over the fins, or is blocked internally, it should work. There are no moving parts.

Before doing any of the above, I'd want to see at rest pressure and ambient temperature, running pressure & ambient temp, HI & LO, and center outlet temp. I'd also want to see the pressure readings when the clutch releases, and when it re-engages.

Cycling can be due to 1)high head pressure - HPCO, 2)low evaporator pressure - LPCO, or 3) weak clutch, 4)too much/little gap, 5)clutch power problems such as bad brushes or corroded terminals or broken feed wires. Which do they suggest you have causing the cycling? A condenser can cause cycling only if head pressure rises due to blockage, and you reported COLD air, which you won't get with blockage. I'd like to hear that explanation as it makes no sense from my point of view.

tom


Thanks for all the input Tom, their recommendation didn't make any sense to me either. They claim that they think the cycling is from a worn out clutch in which my reply was then why don't you just change out the clutch instead of the whole compressor and they said well the compressor might be worn out from engaging/disengaging so much that it would be better to just replaced the whole compressor while you're at it. I said alright thanks, grab my keys and left. Haha As far as the pressure readings that you mentioned, I have no clue but I think I'm just gunna invest in some gauges and dig into this myself. I hate that you can trust mechanics anymore, I literally walked away with the feeling like they were just loading there shotgun and shooting from the hip lol


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