OTR A/C Tech question

[Joe Camper]

I am working on a Prevo a CC conversion. I have reconstructed CC's version of OTR A/C that existed on the bus from new but has been inop for 10 or 15 yr.

The evap and condenser and controls and switches I was able to find at red dot. We found a bergstrom compressor tat was an exact replacement for what was in there.

On Prevo that did not come with OTR A/C and are converted often what you get is 2 compressors off the engine 1 is a York and it is there from the factory for the dash loop. CC then adds another compressor and a set of evap/condensers  1 in the lower kitchen cabinets 1 under the bed.

This particular coach eliminated the factory york compressor and installed 1 very large compressor to handle all 3 evaps.  So that would create 2 "loops" 1 loop for the dash and 1 loop for the 2 added evaps and condensers in the back of the bus.

O/K enough background for someone to possibly help out.

After installing all the hardware we sucked it down and it held vacuum . We have a scale and watched what we added.

13 lb of 134a got us to 200 high side and 23 low side it was mid 80s out the air was ice cold at the evaps life was good.

First trip out the compressor locked up and I cant figure out why.

We installed a binary switch at a port on the dryer to protect it from both low and high pressures checked the circut and its good.

Why did the binary switch no shut the compressor off

Could an excessive amount of freon returned to the compressor liquid  locking it without raising the pressures enough for the binary switch to cut it off??

Another question is the original compressor had the limits right off the top of the compressor and the binary switch is on the dryer probably 5 ft away from the compressor itself. Insufficient? Does the limits have to be directly at the compressor like before?

Bergstrom Tech support was not able to tell me just how much additional pac 46 to feed into the system before start-up we added about 4 ounces. Could this have been a mistake.

Thanks in advance.

[stevet903]

Couple of things to check - did you flush all of the lines before you put the new compressor on?  They make a filter to go inline to catch any debris in the system, which is a good idea in older systems.  How much oil was in the system?  When I replaced my York with a Sanden, the book said to add 1oz of oil per 10 feet of hose, + 1oz extra.  I put in 11oz extra over what was needed for the compressor - 40 feet up, 40 feet back, 15 feet in the rear +1 oz.  Here's the Sanden Manual - http://www.sanden.com/originals/images/SD_Service_Guide_Rev.2.pdf.  With two loops you probably need even more.

Steve

[Joe Camper]

Good info thank you yes we flushed out everything. A substantial amount of oil came out of when we did but difficult to impossible to know exactly as it is being blown out.

The previous setup was r-12 everything flushed out good tho. New expansion valve on the drivers evap. Two completely new red dot evap assemblies for the kitchen and bedroom. Each evap has its own solenoid on the high side line to stop the flow if the fans aren't running or the internal thermostat gets too cold. Power to the compressor clutch has to come thru the drivers loop high side solenoid it powers up with the dash fan, that is the "proprietary" loop. Replaced all the failing dc condenser blowers and ran power to them with new circuts with relays.

I know that the compressor still had the correct level in it it has a sightglass.

According to your formula maybe 14oz or so.

we introduced it at the compressor under vac and simply sucked it in thru the hose for a bottle and shot a 1/2 pound or so of freon in after it. Manually turned the compressor 10 or 12 times to clear it and proceded to run things adding freon. 13 lb got us to 200 high side 23 low side it was mid 80s outside and we had almost 20 degree drop across the evap on all of them.


System ran for 5 or 6 hr before the compressor locked up.


Need to find out exactly what the mistake was before charging it again.

I do not understand what a binary switch is for if it cannot protect from this

I say I need pressure switches high and low right at the compressor.

Havent opend the link yet thank you again

[luvrbus]

Joe, ackits.com has forum for ac units good folks maybe they can help fwiw I know CC had a sag,trap or a loop whatever you call it in line for those systems for extra oil or they died from the black death as they called it lol.
CC has a few people working now sure they can help also  

good luck

[Joe Camper]

frigicool or some such manufacturer that is who did the original stuff. No longer around No matter.

CC does a good job on tech support but there is little they can do here. I need the tech at bergstrom the manufacture of the compressor to step up.

I spoke with him before the install about using a binary switch on the dryer 5 ft of line away from the compressor instead of the high and low switches directly at the compressor originally he said it"should" be OK, AND how much additional oil to add to which he had no definitive answer. 

What do you mean the black death you lost me.

I could not open that link??

[luvrbus]

www.ackits.com should work Joe

[Zeroclearance]

Joe, just for a reference.  Prevost specs out 7lbs of 134a for the York compressor/drivers A/C.

[robertglines1]

plus extra 6oz of oil for the line length. to front

[Joe Camper]

Thank you.  Went and dropped off the compressor and it looks like they will  warranty it. It is an unusually large compressor and it attracted a bit of attention. One of the techs that was looking at it began asking all the correct questions and after some conversation I came away with 1 thing he suggested for sure.  The hose, all the original remaining hose as well as the changeover from r-12 to 134a. They would not do a change from r12 to 134a without all new hoses.

I am going to reflush all of it and see what comes out he thinks black and the rest of the remaining original hoses are breaking down plugging up the works. That failure can possibly cause the compressor to make vacuum and self destruct is what I took from his description.

He was also pretty confident that the new location of the high and low pressure switch at the dryer 5 ft of line away from the compressor itself was a non issue.

I am going to open up all the connections at the evaporators and condensers flush everything again and see if it still comes out clean. Check screens in the expansion valves.

The hose for the dash loop it is prevo factory stuff. Aeroquip and running thru tubular chases front to back. A project but doable.  Some of the stuff for the CC add on is not accessible

It was the first link I could not open thanks again.

[luvrbus]

Joe, that Co you mention was bought out by ProAir of Elkhart IN fwiw I have 2 of those units I bought from Northwest Surplus in Eugene same unit CC used in the upper class RV's

good luck

[Joe Camper]

Zero Clearance we had the charge very close I measured what went in it was 13 lb so almost twice the amout for just the dash loop at7lb.  200 high side 23 low side on an 85 degree day 20 degree drop at the evaporator and swetting profusly. That was pretty close I think.

I am just happy they are going to warrenty it and I will be able to answer more questions after I have flushed it out again and see what does or doesn't come out.

Wonder what the cost is on 2 40 ft pieces of aeroquip a/c hose 1 #8 and 1#12? Gonna find out.

Thanks Luverbus. This is a very tough project for me thank goodness he lives close and he is patient. I do not believe there are 2 out of ten early 90s CC prevo conversions that have this stuff still working. I myself have not seen any early 90s CC prevo conversions with it working. None.

Thank God I was lucky enough to buy a bus with factory OTR A/C when I bought ours before I even new what the heck I just bought LOL

[luvrbus]

I pay around 3 bucks a foot for #8 and 4+ bucks for #12 depending on the manufacture or if reduced or standard barrier it will be 500 bucks for 2 the hoses by the time you are through lol

good luck

[kevink1955]

A question first, how is the trianary switch located on the dryer only 5 feet from the compressor?
The dryer should be in the liquid line and the condensor should be in between it and the compressor.Either way the switch should see the high side pressure just the same (within a few psi)

Is there a chance that when the evaporator solniods open the liquid floods back to the compressor before the expansion valve can regulate it?

An overcharge would make the flood back even worse.

I have done many R12 to 134a conversions on emergency vehicles and never replaced the hoses or had any problems with them but have to say the hoses are not 40 feet long like you have. I also have no use for flushes as it is hard to get them out of the system. An old timer once told me nothing but oil and refrigerant belongs in a system and I still follow that rule.


I

[Nick Badame Refrig/ACC]

A question first, how is the trianary switch located on the dryer only 5 feet from the compressor?
The dryer should be in the liquid line and the condensor should be in between it and the compressor.Either way the switch should see the high side pressure just the same (within a few psi)

Is there a chance that when the evaporator solniods open the liquid floods back to the compressor before the expansion valve can regulate it?

An overcharge would make the flood back even worse.

I have done many R12 to 134a conversions on emergency vehicles and never replaced the hoses or had any problems with them but have to say the hoses are not 40 feet long like you have. I also have no use for flushes as it is hard to get them out of the system. An old timer once told me nothing but oil and refrigerant belongs in a system and I still follow that rule.


I

Just to add to Kevi's statment,
An overcharge is what I'm thinking also.. With two evaps, the TX valves will never work in complete unisin. This can easly
fool the installer if not carefull. When all else fails, always go by a sweatback to the compressors. This means be aware of
when you see/feel a sweatback on the suction line when charging. I'm thinking you may have been freezing back on the
suction line which will cause flooding of liquid into the compressor and damage will result..
With your new compressor, charge the system slowly until you have a cold sweat at the suction line.
The imballance of your system will overflood one evaporator when the other is tempature/selonoid valve satisfied.

Good Luck
Nick-

[stevet903]

Joe - I got my AC hose here - http://aeroquip.cc/aeroquipfc802hose.aspx

Steve