It started doing this fairly recently - no work has been performed - it just decided to not work right one day...

The A/C compressor will not engage until after the engine is hot - the idiot gauge on the dash has to be firmly in the middle. After it engages, though, hoo boy does it blow cold - which is great, except I didn't used to have to wait as long to get cold air... It does cycle.

I thought, okay - low coolant - I get one of those refill bottles of r134a (w/ "conditioners" and whatnot) with an attached gauge at walmart and pump it into the truck - no change. Gauge was cheesy - told myself to get a better one.

I wait a while and get another bottle of refill r134a - one with a better gauge on it - and try again. Truck doesn't want any more - I may have overfilled, but there's no change - before the compressor kicks in, the gauge reads in the red - overcharge - but once the compressor kicks in, it drops and starts reading in the green and, when I checked per ambient temp, it was a bit in the high-end of the green for that temp, but was fine. I have no way of checking the high-pressure port.

Is there a temp switch of some kind on this system? I don't think it's low on r134a, but something is keeping the compressor from kicking on like it used to.

 

Yes most A/C Systems have a Low/High pressure safety switch to shut it off to avoid damage to compressor


Need to somehow get the Low Side back to the right PSI see what happens

To Really troubleshoot A/C As you know you need gauges for High and Low Siddes and a DVM to Check the electrical side of things

You could Also have a Open clutch wire harness that heated up and closed the connection and turned on hard to say Given what has happened Now

 

I need to track down some guages. I checked it over for leaks again yesterday, but didn't find anything obvious. The system is still under pressure, though. It seems I was wrong about it cycling - it doesn't seem to want to cycle until after it decides to engage the compressor.

Sent from my Nexus S 4G using IB AutoGroup

 

The first thing I would check are the HPCO and LPCO switches when the engine is cold. They should both be closed, as the pressure should be above LPCO temp, mid-high 20's and below the HPCO pressure. If one is open, your clutch won't engage.
If they are both closed, connect an indicator light to the feed to the clutch, and ground it. It should light whenever power is provided to the clutch. Work your way back through the switches to see where you lose power. To my knowledge, there is no provision for an A/C cutout due to low temperature except the LPCO. The WOT cutout is operated by the computer, I believe.
If you have an 'automatic temperature controlled' system, I'm ignorant. There are a lot of inputs that affect operation. There are also fail-safes that will prevent operation until things are repaired, or conditions change. As an example, a Honda system has a PWM control for the blower motor that will cause the system to stop A/C from working at all if it fails. And the system detects the failure. The blower will still work in High, but not the lower speeds, so the 'auto' can no longer 'auto'...
You might want to read up a bit more on symptoms of low refrigerant before jumping to the easy solution of adding a bit. You may now have an overcharged system that will not perform as well as one that is properly charged. Many techs no longer want to charge by pressure, and instead want to do an 'exact' charge by weight, using the manufacturer provided spec. You now have a system that has an unknown charge.
tom

 

I haven't done any work on it - I've been looking around here locally for someone who knows how to work on these systems...

But, in the meantime, I did notice something else. When the engine gets up to max temp (I'm assuming it's max, at that point), I hear a noise, like a "thump" - it seems to be coming from either under the dash or around the firewall. All of the heat/cool functions seem to work fine so, I don't think it's a blend door. When this "thump" happens is when the A/C decides to start working, though - which I find weird...

 

If the temp control, or 'blend' door got stuck, you might have high temp until it frees up and moves to the 'cool' position. In that case, you'd have high outlet air temp, or at least warm as the coolant heated up. You might try removing the glove box and looking at the linkages and control stuff on the plenum and watch as the engine heated up. If you see things move as the 'whump' occurs, you'll have a good idea of what's going on.
tom

 

That thump you hear is the compressor engaging.

 

Lets think about this some more.

You may now have more than one problem.

I'm not clear on When you added charge to the system, but if it was blowing cold to begin with, before you added 2 more cans of charge, it likely didn't need more & now is likely overcharged.

Before you added the 2 cans of refrigerant, did you raise the hood to see if the AC clutch was engaging/cycling when the engine was cold & you were calling for cooling??? Or were you in the cab & just guessing it wasn't engaging, because the blend door was acting out?????

The whomp/thump sure sounds like an acting out blend door problem & if its sticking, or otherwise acting out because of a control system vacuum leak, it'll sure mess with the air conditioning the system puts out.

So I agree & like tomw's ideas on checking/servicing the AC system. Check the pressure switches as he suggested, before you turn the system on & if they check out ok & you've over charged, which it sounds like you might have, resolve the blend door operation question first, (whether its arm is broken, or the AC control system has a vacuum leak), then run this puppy by a trusted AC shop & explain you think its over charged & have them evacuate the system, then re-charge with the proper Type & Weight of refrigerant. More thoughts for consideration, let us know how it goes.

 

Alright, I thought I had already covered all of this in prior posts but, apparently, I didn't do a very good job of explaining myself - let me see if I can clarify this a bit...

1. I first noticed there was an issue when cold air didn't flow from the vents like it usually did when I turned the a/c on.
.....1A. This was not when I initially tried to recharge it.

2. After doing some initial research, I waited until the truck was cold, then I started it up; turned the a/c on "max"; and turned the blower speed all the way up.
.....2A. It was at this point that I observed the following:
..........2A1. The compressor was not engaging.
..........2A2. The compressor was not cycling.
..........2A3. After the truck warmed up to its 'max' temp (the temp gauge on the dash reads dead center at this point), there is a "whump", or "thump" sound that can be heard and the a/c starts working like it should. When it does start working, it blows cold - not before then.

3. I attempted to research the symptoms online - everything I was reading was indicating that the symptoms I was seeing was indicative of the coolant being low.
.....3A. I performed a visual scan to see if I could spot anything obviously wrong - I found nothing.
.....3B. Not knowing anything about the prior service history of this truck in regards to the a/c system and, given that the truck is 10-years old, it made sense to me that it could be possible for the coolant to be low.
.....3C. Based on the information above, it was only at that point that I decided to try pumping more coolant into the system to see if anything would change.

Now, here's where things get a bit sketchy - It is known that those goofy little gauges they put on those refill canisters only read the low pressure - not the high pressure so, it's not a fully accurate reading of what's going on - also, some of those gauges they put on those bottles don't work all that well. The gauge on the first bottle I put in didn't indicate an overfill problem - it wasn't until after I put the second bottle on (with a seemingly more accurate gauge) that it started reading that the system was overfilled.

Nothing has changed therefore, the issue of whether it's overfilled or not seems irrelevant to me, at this point.

4. I had thought of the blend door issue. I worked the controls around and it seems to be working just fine - it's not stuck on any one temp or function - all functions work in regards to heat and ventilation - the a/c, of course, kicks in after the "whump". I can hear the doors working. I will, however, add the removal of the glove box to visually inspect the blend doors on my list of things to do anyway - one never knows.

I have not gone through tomw's suggestions yet, but I will. I did do a visual inspection of the wiring harnesses and plugs and found nothing wrong. I did not find any vacuum lines disconnected. The battery terminals are corroded and I'll be taking care of them. I'll also be checking the relay again although, I think it's fine.

I'm also in the process of trying to find a competent a/c repair person somewhere along the coast here - or someone with a proper set of gauges...

 

OK, on the delayed compressor start, swap, or replace the under hood power distribution box located AC power relay, for a known good like one not needed to run the engine. The power relays are a known problem part & I've heard of heat sensitive ones.

If the AC was blowing cold air when it decided to turn on (before you added the two cans of refrigerant) it may now be over charged & should be checked with a set of gauges, or evacuated & recharged by weight imo, to prevent possible overcharge damage. You can buy a set of AC manifold gauges that are good enough for occasional home use, from Harbor Freight for about $50.

 

Just an update...

Following up on tomw's suggestion, I checked the HPCO and LPCO switches at KOEO and engine cold - both were closed.

With engine running and A/C on max, I get a solid 14.5VDC reading on both plugs feeding the HPCO and LPCO switches and, by unplugging and plugging the harness back in, you can definitely tell the switch is working.

So, I guess I'll cross those off my list... Haven't found the right relay yet - went to grab the user's manual and realized I buried it somewhere - gonna have to look it up online, LOL...

I'm also thinking that "03 Maz B23" might be correct about the source of the "whump" or "thump". I was keeping an eye on the compressor the whole time I was there checking wiring harnesses, plugs, and whatnot - it didn't cycle once the entire time until the temp finally triggered it (it's consistent each time as to when it will kick in) and when it did, it was like BAM, it's on - the compressor kicked in, bogged down for a bit, then picked up steam and away it went...

There's a Ford dealer in Coos Bay - I'm thinking I'll just take it to them to figure out...

 

You might check the clutch gap as a too-large gap will make engagement 'clunky' and possibly intermittent. That could explain why it won't engage until everything is warmed up. There is a specification of how much distance there should be between the drive and driven faces. It is adjustable by moving shims from one side of the clutch to the other, front to back. Add shims 'behind' if too close, move them in front of the cltuch if too far apart.
tom

 

But then you would need a clutch hub puller to adjust the gap, ect ect, let a shop take a look for ya, you already took some lumps, 2 cans of 134a, probably an over charged system and the cans he added could have cantained an oil charge or leak stop. Now the o-tube is going to be plugged up. Thats why you need a licence to play with a/c. There is no doubt there is a problem, a/c should kick on as soon as the switch is turned on. hub gap, open wire in clutch coil sounds right, relay in underhood fuse block, have seen many times. but one important question we never asked is this a manual or automatic system, the body module could be holding off the air for some reason. there's just to much to put on a thread and yes it does have a HPCO another can of 134a and someone could get hurt. Take it in, let us know and we will all hope it doesn't sting to bad.

 

Seeing as how you can't find your owner manual, here is a link to it. http://www.fordservicecontent.com/Fo.../04ranog3e.pdf
At the bottom of Page 146 is the pictorial of the 3.0 & 4.0L engine under hood power distribution box fuses & power relays. Position 46A is the AC clutch power relay. Try giving it a thump, or wiggle when the engine is cold & your calling for cooling & the AC isn't running & see if it'll turn on. If it does, remove the power relay & check its contacts/pins/sockets for loose fit, or corrosion. If you find corrosion, tidy up with a good electrical contact cleaner spray, like CRC QD & apply a good electrical contact lube product, plug it back in & see how it goes.
If no joy, try swapping the AC power relay with a known good like one not needed to run the engine & let us know how it goes.

I'm not clear on if you believe you discovered the source of the woomp/clump sound while you were working under hood & the AC compressor turned on after things warmed up. If the sound is in cabin & you think its the blend door, check its in cabin fuse panel fuse contact, to make sure its tight fitting & without corrosion. Did you ever remove the glove box so you could check the blend door control arm, to make sure it isn't cracked, as that's a common problem area in blend door operation woes.

If no joy on these thoughts, probably a good idea to take it in & let the Dealer have a go at it.

More trouble shooting thoughts for consideration, keep us posted on your findings.

 

My a/c has always has always had a very positive clutch engagement accompanied by the thump. ( Sounds like someone giving the fender a good kick). Done it since day one and 11yrs. later it is still putting out the big chill without any problems.