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Old 06-05-2021, 10:47 AM   #1
Skoolie
 
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Carrier Transcool Air Conditioning help

2004 Blue Bird All American, 40 footer, has the Carrier Transcool Airconditioning unit on top. This bus came from Tempe Union High School District in Arizona.

If anyone has played with these before, I've looked all over, can't find any sort of fuse box or controller. When the inside unit fans are on, the roof unit fans come on, everything works except for the compressor. I've tried charging it with R-134, the compressor clutch does not engage, no signs of life. So it doesn't take the refrigerant.

It seems there is one two conductor wire that runs to the dash control panel that may be the switch, but no matter which way the switch goes, no action.

I don't know if it is a low pressure switch, or there's a fuse out somewhere, or what. I have no documentation.

Any tips or tricks before I drop $$$ to take it to a shop?

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Old 06-05-2021, 11:49 AM   #2
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Originally Posted by WiredForStereo View Post
I've looked all over, can't find any sort of fuse box or controller.

Any tips or tricks before I drop $$$ to take it to a shop?
My BlueBird has all the control panels for the two A/C units in the electrical box under the driver's side window. Mine are "Rifled Air Conditioning" units, though.


I thought you are an engineer? It's just A/C. Simple electrical circuits and simple mechanical parts. I knew nothing about mine, and fixed and restored it. But then I'm a mechanic/technician (can I call myself a "tech" without being pretentious?).
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Old 06-05-2021, 12:32 PM   #3
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what is your standing pressure when you checked with a gauge? your compressor on those likely needs to see pressure above 40 or 50 (typical) for it to start..


if thats a rear engine bus, the A/C relay box is often located on the back wall of the engine compartment.. (toward the front of the bus).. ive also seen them on te back deck under the rear window...



check the wire going to the compressor, more than once ive seen this pull apart from someone performing service on the system.. if it has wire loom you can peel that plastic loom back carefully and see if there was a splice in the compressor wire.



most often the low pressure switch is located on the Receiver / drier which lives at the condenser. .



if I know what model number your inside and outside units are i can look up the wiring diagrams for them.. i have most of the service manuals for those
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Old 06-05-2021, 05:41 PM   #4
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what is your standing pressure when you checked with a gauge? your compressor on those likely needs to see pressure above 40 or 50 (typical) for it to start..
Zero. When I hit the valve on the can, it goes up to the pressure of the can. Doesn't seem like it's going anywhere.


Quote:
Originally Posted by cadillackid View Post
if thats a rear engine bus, the A/C relay box is often located on the back wall of the engine compartment.. (toward the front of the bus).. ive also seen them on te back deck under the rear window...
Rear engine bus, no boxes back there that I can find. There is only the one double conductor wire that runs to the bus fuse box by the driver, plus the one main power wire from the 24v alternator going up there too. I'm no realizing that that concoction of breakers and relays is probably the A/C control box I'm looking for. I'm attaching pictures. This seems super goofy to me, as there is a huge amount of wiring that has to run a long way to run these blowers. When I do the roof raise, I may end up rewiring this. I plan to put thermostats on the blowers anyway.



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Originally Posted by cadillackid View Post
check the wire going to the compressor, more than once ive seen this pull apart from someone performing service on the system.. if it has wire loom you can peel that plastic loom back carefully and see if there was a splice in the compressor wire.
No wires disconnected that I see. I could get the multimeter out and start checking voltages, but there seems to be three sets of wires coming from the alternators, one big fat one that is obviously power, one medium double wire that goes to the control, and one small pair that goes to somewhere on the compressor. If I had to wager a guess, that might be the one that has something to do with actuating the clutch?



Quote:
Originally Posted by cadillackid View Post
most often the low pressure switch is located on the Receiver / drier which lives at the condenser. .
As you can see in the pics, there are pressure switches on the compressor.



Quote:
Originally Posted by cadillackid View Post
if I know what model number your inside and outside units are i can look up the wiring diagrams for them.. i have most of the service manuals for those
Great, can you see anything from the pics? What am I looking for?

Thanks for the help, I really appreciate your assistance.
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Old 06-05-2021, 09:08 PM   #5
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I have a similar if not the same AC system. The picture of the relays are the bus relays. The AC control box in my bus is mounted in the interior of the bus on top up the rear deck above the engine. It is a large black box which would be hard to miss if that is where it is located on yours.

Ted
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Old 06-05-2021, 09:42 PM   #6
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Are you still down in Tempe? If so, AZ Auto Air in Tempe is one of the few places I've encountered that's happy to work on our non-standard-car air conditioners. They're pretty fantastic.

https://azautoair.com/
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Old 06-06-2021, 01:57 AM   #7
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If you have the same AC as I do with the em-17 evaporator this is the manual. Pictures of all your AC components would be helpful for identification.

https://www.google.com/url?sa=t&sour...Sag2fURSWd6h6r

Ted
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Old 06-06-2021, 06:17 AM   #8
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if the gauge shows zero pressure when conecting then goes up to the pressure of the can I suspect there may be dirt in the valve or your device isnt able to engage the valve. (we still dont know the true system pressure).. (your gauge should get a reading when you connect it before you open the valve)



are you just using a car charging kit or do you have an actual manifold gauge set? if you have an actual gauge set you can connect the red hose to the high side port and see if that schraeder valve will engage.


Harbor freight makes a really nice and cost effective Gauge set.. you can also jug charge with a manifold set. (that system probably hold 10-12 pounds depending on line lengths)..



since we still dont know the state of charge, it could easily be a low pressure switch tripped out causing the compressor not to run.



that said if in fact the system charge is zero then there is a leak somewhere.. A/C systems simply circulate their refrigerant around in circles forever.. they dont consume it.. so when it ends upo low or empty it means there is a leak someplace.



ironically the valves where you charge a system are often source of leaks.. dirt gets in them from the caps being left off or just general servicing and then a leak occurs..



-Christopher
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Old 06-06-2021, 09:46 AM   #9
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Quote:
Originally Posted by cadillackid View Post
if the gauge shows zero pressure when conecting then goes up to the pressure of the can I suspect there may be dirt in the valve or your device isnt able to engage the valve. (we still dont know the true system pressure).. (your gauge should get a reading when you connect it before you open the valve)
The valve seems to hold the pressure I give it, I tried pushing the valve stem and refrigerant and lubricant comes back out.



Quote:
Originally Posted by cadillackid View Post
are you just using a car charging kit or do you have an actual manifold gauge set? if you have an actual gauge set you can connect the red hose to the high side port and see if that schraeder valve will engage.
Just a car charging kit. I will check into Harbor Freight.



Quote:
Originally Posted by cadillackid View Post
since we still dont know the state of charge, it could easily be a low pressure switch tripped out causing the compressor not to run.
Is that something that can be reset manually or is it inline with the clutch coil?



Quote:
Originally Posted by cadillackid View Post
that said if in fact the system charge is zero then there is a leak somewhere.. A/C systems simply circulate their refrigerant around in circles forever.. they dont consume it.. so when it ends upo low or empty it means there is a leak someplace.
Looking at the bus maintenance records, the system did need to be recharged periodically, every two years or so. And this bus was sitting nearly two years before I bought it. So a leak seems likely. The only place where it seems obvious a leak might be is on the compressor. There doesn't seem to be any build up of lubricant anywhere else. The compressor is a bit mucky, but so is the whole engine, I need to get the power washer out.



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ironically the valves where you charge a system are often source of leaks.. dirt gets in them from the caps being left off or just general servicing and then a leak occurs..
The caps were on when I found it, and they seem clean and serviceable.

Interestingly, I found the original oil cap stuck under the injection lines on top of the engine. So it looks like someone absent mindedly lost it and replaced it with a different one. I can tell because it's painted the same color as the engine.
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Old 06-06-2021, 09:50 AM   #10
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If you have the same AC as I do with the em-17 evaporator this is the manual. Pictures of all your AC components would be helpful for identification.
Similar to that but the condenser fans are not inline, they're offset, four fans, staggered diagonally. I will try to get some pictures.
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Old 06-06-2021, 11:56 AM   #11
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Originally Posted by WiredForStereo View Post
Similar to that but the condenser fans are not inline, they're offset, four fans, staggered diagonally. I will try to get some pictures.
Kind of like this.

I think the link to the manual I sent had charging instructions If I remember right I thought I saw instructions for jumping the low pressure switch to charge the system. I agree with Cadillackid that you should try to find the leak if you can. That system should not have alot compressor oil in the system as the compressor has its own oil supply in the compressor crank case.

To charge a system that size you will need the large r134 propane style tanks. It would eat alot of the small cans.

Ted
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Old 06-06-2021, 04:39 PM   #12
Bus Geek
 
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that would be a wierd can tap if it only shows pressure when the can valve is open.. hopefully thats not the case.. howrever if the system is full of refrigerant then thats one less thing to be concerned with..



the low pressure switch is auto-resetting on vehicles the high pressure typically is also.. when it has enough pressure it will trip the switch and spin the compressor. when I installed my rear unit I put the switch in-line.. if you have a similar switch, you could "jump it" and see if the compressor engages..



my switch si both a low and high pressure.. so its in my liquid (high side) line.. it kicks off below 40 (high side pressure) and also above I think its 350 or 375.. a switch located in the suction (low side) line will be strictly low pressure..

if you do jump the switch , the compressor engages, and youbdont notice any cooling within 30 seconds or so then shut it off..

im not sure if you will have 2 separate switches or one combi-switch.. ive seen them both ways on carriers..



this is what my combi switch looks like.


IMG_2494.jpg
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Old 06-06-2021, 09:10 PM   #13
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Quote:
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Kind of like this.
That is the one, based on looks alone.

Quote:
Originally Posted by TJones View Post
I think the link to the manual I sent had charging instructions If I remember right I thought I saw instructions for jumping the low pressure switch to charge the system. I agree with Cadillackid that you should try to find the leak if you can.
Yes. I'm not super concerned about fixing it permanently right now, just to get it charged for the summer. Just using it as a "tent" this summer, not doing the full conversion until fall/winter/spring. I will be raising the roof and possibly moving the condenser to the back, so all the hoses are going to need to be redone and the whole system reconfigured.

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That system should not have alot compressor oil in the system as the compressor has its own oil supply in the compressor crank case.
That's another thing, I can't tell if the compressor is full of oil, over the sight glass, or has none at all. I guess I need to open it, but wasn't sure if the crank case is part of the pressurized system.

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To charge a system that size you will need the large r134 propane style tanks. It would eat alot of the small cans.
Yes, somebody wrote "12 lbs" on the compressor. I thought maybe I could top it up, but it has been sitting for a while.
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Old 06-06-2021, 09:12 PM   #14
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that would be a wierd can tap if it only shows pressure when the can valve is open.. hopefully thats not the case.. howrever if the system is full of refrigerant then thats one less thing to be concerned with..
No, it works the normal way. Sorry if I wasn't clear.



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if you do jump the switch , the compressor engages, and youbdont notice any cooling within 30 seconds or so then shut it off..
Just need to find that switch.
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Old 06-07-2021, 11:27 PM   #15
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That is the one, based on looks alone.

Yes. I'm not super concerned about fixing it permanently right now, just to get it charged for the summer. Just using it as a "tent" this summer, not doing the full conversion until fall/winter/spring. I will be raising the roof and possibly moving the condenser to the back, so all the hoses are going to need to be redone and the whole system reconfigured.

That's another thing, I can't tell if the compressor is full of oil, over the sight glass, or has none at all. I guess I need to open it, but wasn't sure if the crank case is part of the pressurized system.


Yes, somebody wrote "12 lbs" on the compressor. I thought maybe I could top it up, but it has been sitting for a while.
The crank case is pressurized. I can't remember if it was the manual I sent you or the manual for my compressor that had the instructions for changing the oil. Basically you have to isolate the compressor, evacuate the refrigerant, change the oil, pull a vacuum on the compressor and then open the valves back to the system and then check the level of the refrigerant.

The best place to start trouble shooting is with a decent set of manifold gauges to see what your currant system pressure is. The manual lists the cut in cut out pressures for the compressor. If the pressure is above the low pressure cut out and the clutch will not engage I would check for voltage to the clutch. If the clutch is getting voltage but not engaging you could have a bad electro magnet. If there is no voltage to the clutch I would check the low pressure switch first. It should be located on the compressor on larger line that comes back from your evaporator. It should be open below the low cut out pressure and closed above the low cutbout pressure. If it checks out as ok I would move on to the high pressure cut out. It should be located on the smaller line that goes to the condenser. It should be closed if below the high pressure cut out. There is also a temperature senor somewhere that won't let the clutch engage if the ambient air temp is too cold.

Hope this helps

Ted
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Old 06-08-2021, 06:14 AM   #16
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yep like Tjones says the compressor is pressurized.. there should be two King valves on the top of the compressor, when closed they isolate the compressor from the rest of the system, I dont know that system specifically but on some when the king valves are closed the schraeders only allow access to the compressor pressure.. so it can be drained and evacuated during service.. and when the king valves are open the valves access the whole system.. thats the way the old coach compressors are (My 1965 GMC has a 6 cylinder compressor and holds 33 lbs of freon)..



its possible the king valves are closed now from someone trying to service the system or perhaps deemed the compressor bad? its probably worth checking those before going too much further...



the sight glass.. Ive worked on more than one system. where it had a leak and people kept charging in dye and stop leak till no end which puts non condensable liquids in. and resultsi n an overfull sight glass or its glazed over.. it could also be empty. which is viable if the system got a leak. it will blow its oil out along with the freon... the compressor may have a low oil level switch this is a common thing on some of these..
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Old 06-08-2021, 11:01 AM   #17
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I appreciate your advice and help.

Next question, is it worth it to buy all the gauges and the R-134a (about $10 per pound), and a vacuum pump, or take it to be serviced?

I can do all these things. But I like numbers. How much do you think it will cost me to get it professionally serviced? I prefer to do things myself, but if the numbers are ridiculous, there are some things I'm happy to pay for.
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Old 06-08-2021, 12:00 PM   #18
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im not sure on serviuce cost? ive been building and servicing my own A/C for a long time.. alot has to do with your mechanical abilities.. if there is a leak can you track it down and fix it (replace a section of hose.. replace the O-rings if they are leaking).. it will have to go to a shop that specializes in transport A/C, refrigeration.. it could be $500 or $3000 (not exaggerating) .. or it could be less if all they do is replace a fuse or fix a broken piece of wire someplace..



the only reason I mention gauges is because something seems off with the can tap / gauge you are using.. does the system have any pressure or not? the gauge reads nothing then you pull the trigger and it does.. it could be the service valves are the type which is 3 position and the service port is closed off.. they could be 2 position style that are on / off. (compressor isolation). I cant see the service ports / valves in the pictures provided..



these are the style on my GMC..



https://hvacrschool.com/compressor-m...ervice-valves/


they are 3 position. you back them out all the way to close off the service port and the system operates..



you screw them in mid way if you are runnign the system and adding charge..


you screw them in all the way to isolate the compressor (for oil changing / adding)..


ive always called then king valves though purists will roast me for it
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Old 06-09-2021, 05:10 PM   #19
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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.
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Old 06-10-2021, 12:35 PM   #20
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the only reason I mention gauges is because something seems off with the can tap / gauge you are using.. does the system have any pressure or not? the gauge reads nothing then you pull the trigger and it does..
There seems to be a little bit of pressure, maybe, but I don't know if that's in the system or just the stuff I've tried to push into it. It is definitely below the fill line.

When I do this in cars, about once a year, I just idle the engine, push the trigger and it sucks it up. The compressor here won't turn.

Looks like about five pressure switches on the compressor.

If there is a leak in the system somewhere, it must be around the compressor, it's covered in grime, no other spots where anything is obviously leaking.
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