| Author |
Message |
Setzer (207.144.212.43)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 18, 2002 - 7:25 pm: | |
I am trying to convert a 1694 eagle over the road AC to R 134, can anyone tell me what the low pressure and the high pressure should run?
Other than changing the oil and refrigerant what else is required? Thanks Robert |
Tom Caffrey (Pvcces) (12.146.33.208)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 18, 2002 - 10:29 pm: | |
You need to find out if you need to change the expansion valve. A refrigeration man ought to be able to tell you.
M2CW
Tom Caffrey PD4106-2576 |
Bud (12.87.152.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 19, 2002 - 8:09 am: | |
Your high and low pressures will vary in relation to several factors, most importantly the ambient temperature at any given time. 134 pressures, however, run about the same as R-12. Your local a/c supply house should be able to provide you with a pressure/temperature chart.
It is a good idea to change the expansion valve to the proper 134 valve. Also, the POE oil used with 134 is not compatible with the mineral-based oil used with R-12 (or R-22), nor is it compatible with the lines used for 12 & 22.....so it is a good idea to change the lines out as well.
In order to get rid of all the old oil that has migrated out thru the system, once you make the change you should run the system for an hour or two, pump down and change oil, run again for about 8 hours, and change the oil again. By then, your system should be clear of the old oil.
134 has a longer pull-down period than 12 or 22, but should perform fine once the coach is cool. In my experience, 134 works ok with an O5G compressor, but is not great in a system with a 5F30 compressor.
Good luck |
Jim Nelson (166.90.111.60)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 20, 2002 - 12:57 pm: | |
Ah! There are severe problems in converting to 134a with most systems. The 05G compressor needs to have the valve plates changed to a narrow seat design to prevent the suction reed valves from breaking - for the first three years after Greyhound did the 134a swap, the shop floor would be littered with broken reed valves from April to September, until Carrier came out with a fix. This involves replacing all 3 valve plates, and installing a 45 degree compressor cut-out switch.
Generally, 134a will run at 25-45 psi low side, and 125-175 psi high side, depending on the temperatures inside and outside the bus. For safety switches, a 3 psi low pressure switch and a 275 psi high pressure switch will work for replacing the cut-outs. If your compressor has electric unloaders, then you need to get in touch with a Carrier Transicold dealer for the switch pressures to work those - I don't have them on the top of my head. The safety valve should be 325 psi, especially since it would be a good idea to change all of the flexible lines to 134a service at the same time. The old oil in the system is not a big issue - however, it would be a good idea to drain the crankcase and refill it with PAG oil for 134a service. R-12 expansion valves will work, but R-22 or R-500 valves will need to be changed. If you don't have a 05G, it would be advisable to upgrade to a newer style Thermo King or Carrier compressor - compressors older than the 05G don't like 134a, and have a tendency to leak. |
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