Carrier Transcool Air Conditioning help

[WiredForStereo]

Originally Posted by Walter62

That white box behind the engine maybe the fuse box. That’s what mine looks like. I do not have the AC you have. Although I do have a giant AC compressor that runs off the engine at first I thought it was the air compressor.

Yes, that is the fuse box, there are no AC connections that go into that box. They all seem to go to the agglomeration of breakers and relays on the right side of the fuse box next to the driver.

[Bus'n it]

Most if not all Phoenix area buses that get decommissioned are typically due to non functioning A/C. Mine had a screw from one of the steel side interior transition panels through one of the hoses. Been like that from day one I imagine. They must have charged that sucker every year. Both compressors were shot on mine and one system was completely devoid of refrigerant while the other with the screw in the hose still had very little. The repairs done to my bus were more of a third world duct tape or zip tie repair. All wiring and hoses under the bus were just dangling. No one made the attempt to clip the harnesses or any hoses back to their respective mounts with adel or bolt on zip ties. What a mess. The airbrake dryer has electric tape around two of the compression unions. Good grief! Fun but I can handle it. Clapped out bus is exactly what this thing is. (Benimble, I'm looking at you!) Thats ok. I will fix it. I do not have many friends so when I get discretionary time, The bus has me. You will figure it out. Do not rule out a puncture somewhere. Follow all the lines even if you need to remove a interior panel to check.

[WiredForStereo]

Originally Posted by Bus'n it

Most if not all Phoenix area buses that get decommissioned are typically due to non functioning A/C.

I have the maintenance logs for this bus. The last thing that needed to be repaired that wasn't, was seats and a dead battery.

The AC was topped up with 1 lb of freon and a new belt in August 2019 and it was only driven about 1000 miles after that, and was parked in November 2019 after it had the brake valve replaced. As far as I can tell, it was never driven after that repair, the engine compartment light was left on and the brand new batteries installed in July 2019 were drained stone dead. The light was still on and the batteries still shiny when I showed up in May 2021. I put in new batteries, it fired right up and I drove it 1000 miles home with no issues.

Prior to that, it was given a full charge in April 2019 and passed a leak test, and previous to that, a full charge with a new expansion valve in August 2018, for which there are several entries as they didn't seem to immediately figure out that there was an expansion valve bad.

It was given 4 lbs in November 2017.
4 lbs in March of 2017.
12 lbs September 2016.
2 lbs in February 2016.

Seems like it does leak a little, but most of the problems they had were with the expansion valve in the middle unit. Seems like they didn't catch that for two years or more.

[WiredForStereo]

Okay, so I purchased a piece of junk manifold set from Amazon, which I will be returning, but I got it hooked up and played around with it.

Turns out the reason I was getting weird readings was because there was in fact a valve to open. I discovered this while reading the manual somebody posted, or I found posted somewhere else. Anyway, I have a manual and it has procedures and there's a valve to open to make the ports work.

On the upside, the system was still pressurized.

On the downside, it only had 10 PSI left. Generally, I'm led to believe that two years is not long enough to drain down a properly functioning system. I charged my brother's 99 F450 three years ago and it's still sort of working. So it's obviously the cool juice is going somewhere.

Also good news, I put a couple of cans in from Walmart, the compressor started working. (The master switch seems to do absolutely nothing. The compressor comes on any time the inside unit fans are on. Though, now that I think about it, maybe that controls the condenser fans on the roof.)

The compressor cycles on at 35 PSI on the suction side and off when it gets down to 20, so obviously not enough refrigerant in the system. The hot side hovers around 80 plus or minus.



Does anybody know what kind of stores carry 30 lb cans of R-134a? Or do I just go Ebay? I added about 2 lbs and somebody wrote "12 pounds" in paint marker on the compressor.

Here's an idea I had, tell me if I'm smoking dope. I'm going to do a 24" roof raise, that's a given. I want to remove the rear window and the little angled section that Bluebirds have at the back window (Thomases have it too) and construct it so the back wall is flat and straight up like an international. Then I had the idea of mounting the condenser unit on the back, sort of like how reefer vans have the refrigeration unit on the front wall behind the truck cab. The small problem that I have noted so far is that the unit is 6 feet long and I will have maybe 6 feet and not an inch more in which to mount it. But I don't know how much free space is under the shroud, and I was planning on building a new one anyway. So tell me if my piggy back condenser idea is crap or not.

[cadillackid]

sweet! sounds like the system operates. . and unfortunately has a leak in it.. back in the day I had cars that I charged every summer and just ran them like that.. fortunately my busses dont do that. .



I believe the 30 lb cylinders require a MACS or EPA universal license.. the last cylinder I bought the store asked me for my refrigerant card.. which im always used to displaying when I buy at a supply house so I had it with me..

[WiredForStereo]

Originally Posted by cadillackid

I believe the 30 lb cylinders require a MACS or EPA universal license.. the last cylinder I bought the store asked me for my refrigerant card.. which im always used to displaying when I buy at a supply house so I had it with me..

Ebay it is then!!!

I had to charge my 85 Toyota Pickup every year or so. But R-134a is approaching $10 a pound in bulk, so I ain't into that. The cheapest stuff at Walmart is $5 for 12 oz.

I put UV dye, so hopefully the culprit will reveal itself soon.

As I mentioned before, the compressor was covered in grime, so that's a good place to start looking. Also, one of the valves was sealed in the wrong direction. Given some other problems I've discovered, I'm not convinced that the Tempe Union High School District mechanics were all of the highest caliber. I'll buy some cool juice on Ebay, charge it up for the summer, and see what happens. I'm sure compressors are expensive too.

[WiredForStereo]

30 lb tank of R134 is here.

Will be charging it up here in a few hours.

[cadillackid]

Originally Posted by WiredForStereo

30 lb tank of R134 is here.

Will be charging it up here in a few hours.

if you are good you can flip the bottle upside down and charge very carefully with a liquid boil-off in the gauge manifold..


charging with gas is safe but the bottle can get get cold and lose pressure.. putting the bottle in a bucket of room temperature water can help keep the bottle warm and its pressure up.. of course as long as you dont change anything you can charge by weight by watching the whole mess on the scale and the eight reduces.. you've already put some in and it had some so unless you plan to evacuate and vacuum pump it to 500 microns be mindful that it already has some refrigerant.

[WiredForStereo]

I'm in the Pacific Northwest, so no shortage of heat to boil off some refrigerant. I'll go slow. The bucket sounds like a good idea.

I'm studying the temperature/pressure ranges very carefully, and I have an HVAC tech for a father-in-law, so hoping not to screw it up.

[WiredForStereo]

Welp, screwed it up.

Somehow.

So, my reference materials, several A/C websites, mostly in agreement, said that static pressure should be about 110, for 95 degrees outside.

Plugged in the gauges, said 65 on both, so I proceeded.

Fired up the engine, turned on the A/C, started filling with the tank in the bucket, like you suggested. Whilst filling, pressure hovered around 45 low, and eventually creeped up to 150 high side, for about half an hour, taking it slow.

At this point, it started to concern me because it seemed like a lot of cool juice was gone out of the tank and the pressure hadn't gone much of anywhere.

So I stopped, double checked all my gauges, connections, and reference materials, for 95 degrees, they all say 45-50 low side and 275-300 high side.

So I though, well maybe the "12.0 lbs" written on the side of the compressor is incorrect. Let's see what happens, keep an eye on the gauges.

So I kept filling. Bout the time the tank was nearing empty, it topped out at 50/200, this was all at high idle, 1200 rpm.

Then the tank was empty and I'm perplexed so I tested at different engine speeds, at 2k rpm, it was about 20/200, 1200 was about 190/21, 700 was about 30/170.

Learned the compressor only turns on when the rear blower is on.

Anyway, something happened. But the A/C works, blows nice and cool now.

Perhaps there is a leak that starts blowing off at 150-200?

[cadillackid]

yowsers!!! 30 lbs in a 12 lb system? either you have a hell of a leak asnd it will be empty in an hour or you filled the whole damn condenser with liquid and essentially reduced its capacity while runnint the head pressure up..



these systems are TxV's TxVs work on pressure and also suction line temperature.. so when the suction line (return back to the compressor) is warm the valve opens so more liquid can flow into the evaporator.. the result is a raising of the suction pressure and also keeping the head pressure low.. when the system is low the result is a mix of gas / liquid entering the evaporator so your temperature doesnt drop much and neither does the pressure.. as you get some more charge in, the suction line starts to get cold (unless the space you are working is basted hot.. in fact the only way I charge an A/C is with all the windows open and a fan blowing in.. I want my coolin g load to stay as constant as possible.. I dont want the A/C to catch up.



if you grossly ovewrcharge a system.. the condenser fills up with liquid and has much less space with which to condensr hot gas into liquid and the head pressure rises.. the suction presure likely rises a bit too as the freon on the cold size doesnt get as cold as it should.. and you get wonky readings.. the TxV tries to adjust but cant and your A/C is cool but not cold esp uhnder high load.. or you run the pressure off the scale and it shuts off the system..



the compressor likely only runs when the blowers inside are on.. running it without will freeze it up..





TxV is tricky to charge for a newbie.. alas why I mentioned the scale.. my preferred way since I have tanks recovery units and vacuum pumps wouldve been to vac the system down to 500 microns or as close as i could get and then punch in about 11 lbs and trim charge the rest to see if exactly 12 lbs is the propewr charge.. you likely already had close to 2 in it as a hunch..



now that said.. thise cylinders you buy are one-use and one-way abdsolutely DO NOT try to pump freon back into the can.. it should (to be legal) have a check-valve in it so you cannot do that..



at this point i would get your father in law A/C tech over there with his recovery machine and a Freshly vacuumed recovery cylinder and his gauges and his scale..



measure the emopty bottle and recover the system flat.. measure the weight.. run his vacuum pump on it and then punch 12 lbs of that freshly recovered 134a right back into the system and watch it run.. you want a day over 80.. 1200 RPMS is perfect.. all windows down ..


something seems off if you slammed 30 lbs into that thing and didnt blow the compressor to hell or cycle out on high head but if its a large capacity condenser you may have just filled it up with liquid.. maybe you got lucky and one of your hoses was loose and a good bit leaked away??

[TJones]

It sounds like you have way over charged the system.

If you read the manual I sent you it has specific instructions for charging the system and checking refrigerant levels.

If I remember correctly you are supposed to get the refrigerant in "super heat" state with the high side at around 150 psi at 90 degree ambient temp. You then locate the sight glass in the liquid line running from the condenser to the evaporator. It should be half full of liquid.

I see my earlier link didn't work. Here is the manual.

Ted

[WiredForStereo]

Originally Posted by cadillackid

yowsers!!! 30 lbs in a 12 lb system? either you have a hell of a leak asnd it will be empty in an hour or you filled the whole damn condenser with liquid and essentially reduced its capacity while runnint the head pressure up..

I have been attempting to test that by leaving it sit all afternoon with the gauges on to see if it leaks down. It has settled at about 105 psi and slowly dropping with temperature which seems to be expected. I don't know where there could be a big hole, I've gone over the whole thing with the UV flashlight more than once now, no sign of leaks, at least not below the roof.

Originally Posted by cadillackid

if you grossly ovewrcharge a system.. the condenser fills up with liquid and has much less space with which to condensr hot gas into liquid and the head pressure rises.. the suction presure likely rises a bit too as the freon on the cold size doesnt get as cold as it should.. and you get wonky readings.. the TxV tries to adjust but cant and your A/C is cool but not cold esp uhnder high load.. or you run the pressure off the scale and it shuts off the system..

Suction side was cold, dripping a little condensed water on the metal fittings, nothing looking unnatural. Like I said, I could never get the pressure up to what was expected.

Originally Posted by cadillackid

TxV is tricky to charge for a newbie.. alas why I mentioned the scale.. my preferred way since I have tanks recovery units and vacuum pumps wouldve been to vac the system down to 500 microns or as close as i could get and then punch in about 11 lbs and trim charge the rest to see if exactly 12 lbs is the propewr charge.. you likely already had close to 2 in it as a hunch..

How do you trim though? When is it full? What do the gauges say when it is full? This is information I am lacking.

Originally Posted by cadillackid

at this point i would get your father in law A/C tech over there with his recovery machine and a Freshly vacuumed recovery cylinder and his gauges and his scale..

Unfortunately, he has selfishly decided to extend his vacation in Yellowstone, so he's not going to be here for another week or two.

Originally Posted by cadillackid

something seems off if you slammed 30 lbs into that thing and didnt blow the compressor to hell or cycle out on high head but if its a large capacity condenser you may have just filled it up with liquid.. maybe you got lucky and one of your hoses was loose and a good bit leaked away??

I know! Something didn't seem right. The pressure never got up to where I was led to believe it should be according to the ambient temperature.

The troubleshooting sheet I was looking at has plenty of ideas for low/low pressure with warm air. But I didn't have warm air. The air was cold. High/high pressure with some cool is supposed to be overcharged. I never had that. I never had any indication that the pressure was too high. It never went over 200. And the suction side liked to run in the low 20s when at steady state, which again is well lower than what I was led to expect.`

My static pressure is right where it seems it's supposed to be. Maybe a touch high, but the engine compartment and bus body is still higher than the outside air, so it doesn't seem too far off.

Yeah, I don't understand. I really should have stopped when it felt like half the can was in. But I didn't. Live and learn.

As far as how much the system can hold, it's a 40 foot bus, long hoses, three evaporators, large condenser on the roof. I haven't seen under the hood on the condenser.

[WiredForStereo]

Originally Posted by TJones

If I remember correctly you are supposed to get the refrigerant in "super heat" state with the high side at around 150 psi at 90 degree ambient temp. You then locate the sight glass in the liquid line running from the condenser to the evaporator. It should be half full of liquid.

I'll have to see if I can find that. Would it be in an easy spot or am I going to have to get up on the roof and pull the hood?

Mine is an older system, it's not exactly the same as the manual.

[cadillackid]

stanbding pressure means nothing.. except that the system isnt 100% full of liquid or in a 100% gaseous state and super low..



A/C systems can be measured in different ways.. if the book has subcooling and superheat numbers those are a good place to start.. otherwise you can charge by PT chart.



in a normal charged system the saturation point of the refrigerant will match the little temperature scale on the gauge or you can see the pressure measure the temperature and look it up in the chart.


here is such a chart.
https://www.forane.com/export/shared...ture-chart.pdf


in a simple form you can try and aim for 10-13 degrees F of superheat..



with my fancy gauges and an app called MeasureQuick along with humidity and temp probes it does my hard work for me.. but you can do it yourself.



with a pretty accurate thermometer measure the suction line temperature right as it exits the evaporator. I do it close to where the test bulb is on the pipe for the TxV..



now you look at your low-side gauge pressure and look up the pressure in the PT chart..



if the chart comes back at 40 and the suction line is 52 you have a 12 degree superheat.. this is a very simple and approximate way to do it.. some people like to measure temperature a little ways into the evaporator coil where the boil off is beginning and compare it to the gauge reading and take an average.. others like to go through the highly complex science math and calculate the perfect saturation temp (boiling point) of the refrigerant in the coil..



but really for all intents and purposes being close it OK..


now lets talk about superheat.. what if you come back and your superheat is super low.. that subtraction number comes back at 1 or 2 or even negative...



negative superheat is caused by gross overcharging where refrigerant is evaporating in the suction line.. in fact if your suction line is colder at the compressor than it is at the evaporator outlet you are so overcharged that it will probably slug and ruin the compressor..



low superheat also can be due to very dirty coils.. the coils are so clogged up with dirt that most of the fan air is bypassing the coils and not pushing heat back into the refrigerant so it remains too cold or as a partial liquid..


expansion valve is misadjusted and allowing too much refrigerant into the evaporator.. sometimes people turn the adjustment screws in desperatin to get an A/C to work right and really foul things up.. (thank god only a small fraction of TxV actually can be adjusted without taking the pipes apart)..




high superheat... you record a number of 25 or 30 in that algorithm.


1. not enough refrigerant.. there is no liquid entering in the evaporator or it boils off horribly quick and the compressor sucks the pressure down so the gauge pressure reads ridiculously low.. you'll often see a lot of ice right on the inlet just past the TxV..


2. broken TxV.. the sensing bulb works from a closed sealed loop of its own "refrigerant". if the TxV itself leaks out its internal loop then it will tend to close down far too quickly and not enough flow is allowed into the evaporator.. high superheat readings occur and / or icing at the inlet..



3. misadjusted TxV.. see number 2 above.. some people have an ailing TxV and adjust it to make up the difference.





one of the telltale signs if gross overcharging is when you idle down your system cant properly pull down the pressure.. the TxV is forced open and the compressor cant pull the low side down for properly saturation.. the A/C will be crap at idle.. low saide will be higher than expected and high side may actually be low because when the refrigerant isnt moving any heat the condenser doesnt warm up to raise the head pressure...



remember when working with superheat..clean coils are a must.. proper airflow is a must.. as constant a load as possible.. open the windows and let the system run 15-20 minutes or so on max cool high fan before taking readings.. you can take readings all along if you wish just to watch but I dont heed any till i see it stabilize and just slowly change.



final thought.. your father in law isnt selfish for extending his vacation for something that isnt an emergency.. (at least one or 2 of us said to use a scale when charging the system....)

[WiredForStereo]

I'm sorry, this is just so much inside baseball, I'm lost. I don't have "fancy gauges" just regular gauges (???)

I used the bucket of water like you said, waited for the gauges to get to the pressure in the charts, and it never happened.

I still have no explanation. The compressor is not destroyed, the air blows cold. There is no ice. What evidence should I be seeing that it is overcharged? What is "TxV?" What pressure should it pull down to when idling?



So, what I'm hearing you say is dump the whole thing and try again and only do 12 lbs (which is a number that is written on the front of the compressor with a paint marker).

[cadillackid]

inside baseball? I sent a link of a PT chart.. yes HVAC is a complex process..thats why there are specialized tools / books / apps / schools and EPA tests / and Techs that charge an arm / leg to fix it I tried to simplify it as much as possible..



im not sure who makes these "ambient temp" charts but they are meaningless they have zero to do with the cooling load on the system if by the time you finished charging the system your bus was nice and cold inside you wont see the pressures in an ambient chart.. esp if the condenser size is extra large (which many bus systems are).. you WILL see the pressures on a PT chart...



someone wrote 12 lbs on it with a marker because perhaps the original tag on the system was lost.. every one of the factory A/C systems for busses ive worked on had a tag someplace.. inside the eelctrical panel, on the prperwork that has the total charge.. most likely the original A/C tag was lost and a mechanic scribbled 12 lbs near the compressor becasue that is what it held after gauge charging or they called the company who installed it and got the charge from the VIN. the initial instalation companies will either charge by gauge using superheat / subcool or the en gineers from the firms who manufacture the compressor / condenser / evaporator and lines have charge factors given to the installers who create the magic number by formula based on the engineering data of the components plus piping.. anyway that 12 was on there for some reason.. I'd start there...



after you got your 30 lb jug I mentioned putting the thing in water and then watching the weight on a scale... knowing you had very little in it... common sense says put in 11-12 lbs.. a little overage or under wont kill it..


on your gauges is a scale, a temperature scale.. they are rings on the gauge face of standard analog HVAC gauges.. those correspond to the pressure / temperature of the refrigerant.. if theres multiple rings one will be labelled 134a.



thats the same data that is on a PT chart..



your standing pressure when the system is off and the bus sits overnight will correspond.. so if you look at the gauge in the morning chances are the temperature number right next to your needle will be the temperature of the spot where the bulk of your liquid is hanging out... that changes.. to say that your standing pressure should be 85 when its 90 outside? who knows.. it might be 120 degrees under your bus or where the refrigerant is hanging out.. (most of it usually lands in the lowest part of the system)... thats why its a terrible way to measure.. it also doesnt give you a full / empty reading as you can have a 50% charged system showe perfect "standing" pressure.. by standing pressure I mean the system turned off after its fully equalized..


so you can leave it as it is and it may work Ok or it may kablooey, it may cool decent, or it may cool like crap in certain conditiuons.. I have no idea im not in front of it.. I know what I personally would do if the bus showed up in my driveway and I knew nothing about PT charts, superheat, or subcool.. .. I would recover the charge with my recovery machine into a FRESH EMPTY recovery cylinder and then I would scale charge the thing with 12 lbs and go drive it on some hot days and see if its nice N cold... .. alternatively you can take it to a shop who will do the same thing.. except they wont have a fresh empty cylinder so they will recover it down and then charge you for new 134a because thats how shops work..



if I didnt live clear across the country id load up my tools and help you sort this thing out in person.. but for what it would cost me in diesel to drive out, fix your A/C and drive home you could buy a scale, a cylinder, a recovery machine and probably a fancy set of gauges that work with the ipad Apps..

[WiredForStereo]

Originally Posted by cadillackid

if I didnt live clear across the country id load up my tools and help you sort this thing out in person.. but for what it would cost me in diesel to drive out, fix your A/C and drive home you could buy a scale, a cylinder, a recovery machine and probably a fancy set of gauges that work with the ipad Apps..

I appreciate that. But at this point, I give up. I obviously don't know what I'm doing, and the internet is obviously not the correct place from which to learn. So, I'll just wait for my father-in-law to get home.

It works, it's not blowing up, the pressure is not too high, I just have to make it through one camping trip.

[Kentucky Dreaming]

Plenty of valuable experience here. cadillackid is the best A/C guy around. It would behoove you to listen...

[cadillackid]

Here’s the thing now that it’s done watch it and observe. Drive it and run the AC if you wish .. the high pressure switch should shut down the compressor if the condenser is over flooded with liquid and loses capacity..

Note how hot the pipe is between the condenser and evaporator .. if it gets hot where you can’t touch it then shut the system down you are running it hard.. it’s normal for the pipe between compressor and condenser to get too hot for touch.

If the compressor shows signs of slugging.. Ie you hear a belt squeal or the engine feels strained even at low drive load conditions then shut the AC off.

If you know what your average cruise RPM is you can run your engine speed up to that for a few minutes while parked to observe how the AC works .. and of all seems fine. You can drive the bus around town a couple times before you embark on your trip to see how it acts. If it passes the site sound and smell test then I say run it…