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Today, I decided to begin my perennial air conditioning maintenance/ trouble shooting on my ’86 BMW, which I converted from r12 to r134a. The system has come a long way; along the way, I’ve flushed the lines, replaced a few lines, replaced all the seals, replaced the expansion valve-twice, rebuilt the compressor-twice, replaced the condenser with a parallel flow unit, and replaced the receiver drier each time I have opened the system. This year, the system actually held all the refrigerant over the winter. Late last fall was when I finished the system work, so it was not really a good testing temperate. Currently, the system works wonderfully at a low fan speed. The vent temperature is cold, the low side pressure, as well as the high side pressure are good. However, the fan speed being on low doesn’t really provide enough cooling to make the car comfortable on a hot day. Anyway, when I turn the fan to high, or medium, the high-side pressure seems to stay fairly steady, but the low-side raises. In general, it increases by about 20-25 psi, and the vent temperature increases, too. I’ve got a few ideas on why it is like this:
The first is that the system is just old, and not designed to work well with r134a refrigerant; however, other people have converted their car satisfactorily, and successfully.
My second thought is that the evaporator (basically the only component I haven’t replaced or altered) is not able to distribute the evaporating refrigerant fast enough as it passes through.
My third conjecture is that the system has some trapped moisture, or more likely some air in it. I’m just not sure there would be that much air in the system, as I pulled a vacuum on the system prior to charging. The only way I can think air would get into the system was though the charging tube each time I put on a new can. Thanks for any thoughts in advance.
-Sam
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If it was air your high side would shoot up. If its hot in the car when you turn
the fan on high, Your putting more heat across the coil so the refrigerant is
boiling off more rapidly. Does the car ever get comfortable on high speed?
Sounds like your not feeding enough refrigerant. Either your under charged
or your metering device is sized wrong or not working right.Just curious , did you replace the R12 mineral oil with synthetic oil ( PAG or POE ) ?
Did it work OK on high fan speed , when you last worked on the system , last year ?
How much R12 is it suppose to hold ? Hoe much R132a did you put into the system ?
You need to bleed ( purge out the air ) the air out of the hoses , every time you take a hose loose . I do not have to worry about changing cans of refrigerant . I use a 25 pound jug of refrigerant ( or maybe 30 pound , have not needed it this spring ) .
Use a scale and weigh the amount of refrigerant that you add .
God bless
WyrThe car really doesn’t become that comfortable after long drives. It seems that from my testing, it will cool a max of about 15-20 degrees (Fahrenheit) from the ambient temperature. It really is not enough to make a difference.
When I flushed the lines, I replaced the oil with Ester oil, which is the recommended oil for the rotary compressor with r134a. The air conditioner has really never worked well- It’s acting very similar- if not the same as it was last year. As I recall, the capacity is, with r12, 2.15 lbs. I think I filled it with about 2lbs, But I really don’t know exactly because of the cans, and I started with a half can; this meant I didn’t have a great idea. I do know the static pressure is about where it should be when considering the ambient temperature.
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