AC Pressure Switch ?
1 Attachment(s)
Still gathering parts to restore my AC in the 83.
Regarding the "Pressure Switch"....I know there is a difference between the R12 & R134 switches. But, I see on the original R12 switch, there is what looks like an adjustment screw. (see pic) Has anyone adjusted this switch to work with the R134 conversion & how was it adjusted? Correct me if I'm wrong, but I believe that the pressure switch would have to be adjusted to a lower setting..... Or....make it easy......is there a direct replacement for this switch? One more thing is that the AC system on my truck had been previously changed over to R134. So, that switch might have been already adjusted.. |
Re: AC Pressure Switch ?
If it's a working LPCO switch you can adjust the cut-in pressure for R134a... if you need to.
Hopefully, there's a HPCO switch in the system now as well. |
Re: AC Pressure Switch ?
Quote:
|
Re: AC Pressure Switch ?
I have adjusted them. don't remember the exact pressure though.
|
Re: AC Pressure Switch ?
Quote:
The refrigerant charge level, orifice size, and the compressor cycling switch are kindof an interesting dance. If the charge level is too low the evaporator will freeze. If the charge level is too high the compressor will suffer and vent temps will rise. As outdoor ambient temps rise the compressor head pressures rise. The LPCO or Compressor Cycling Switch needs to cut out at a high enough pressure that the evaporator doesn't completely freeze and yet not short cycle the clutch. If the pressure is too low and the compressor doesn't cycle the evaporator will freeze regardless of charge level. R134a should be roughly 35°F at 31psi in the evaporator. I wouldn't set the Cycling Switch any lower til you get some runtime on it and observe vent temps and system pressures at around 85°F ambient outdoor temp on MAX AC and max fan. Good vent temps should be around 40-45°F. At the temperatures we're interested in, 20°F-40°F R134a runs @ 2PSI lower pressure than R12. That adjustment screw is sensitive... One eighth turn counterclockwise lowers the cut out pressure approximately 2 PSI and one quarter turn lowers the cut out pressure approximately 4 PSI. E38.org refrigerant pressure vs temp table http://johnnynightstick.s3.amazonaws...12R134plot.jpg |
Re: AC Pressure Switch ?
Thank you for the input on this.
I'm thinking that your readings are assuming the orifice has not been changed to a R134 orifice.? I was advised on another thread that the original orifice should be changed when converting to R134. The size recommended was a #61 size. Keep in mind that I'm NOT going to use the original A4 compressor but will be using a Sanden 508 along with a new evap, condenser, dryer & lines..... |
Re: AC Pressure Switch ?
A different orifice will have an effect on cooling but it's due to the pressure change across the orifice.
The compressor choice will affect the volume of gas being moved, how much energy it robs from the engine, and how long the compressor itself lasts. The old Harrison R4 is not noted for longevity and it's a fairly small displacement compressor compared to the Sanden 508 & the old Harrison A6. The A6 is old, heavy, and eats a lot more fuel to run than the 508. You have several different things under your control when you charge the system that affects the temps inside the evaporator and the amount of heat energy the refrigerant moves. You're charging with a refrigerant that the system was not designed for... I use the JungleEddy method for charging the system because it seems to yield consistent results no matter what I choose for refrigerant. However, it's not entirely a recipe. There's some skill involved. That's why I called it a dance. Unless someone suddenly changed the basic gas laws I learned in high school chemistry the published pressure to temp relationship of each of these fluorocarbon refrigerants should be fairly static and follow the table and the graph I plotted in Libre Office Calc as a visual using values from the table. Boyles' law and Charles' Law are the ones I remember as pertinent... http://chemistry.bd.psu.edu/jircitano/gases.html |
Re: AC Pressure Switch ?
Thanks again.....I'll post back on here after I get this up & going......
|
Re: AC Pressure Switch ?
70gm , I have a 82 and used the oem low pressure switch . When I charged it it seemed to cycle to much . I put just a tad more 134 in it ( not much ) . This solved the cycling and had been working perfect ever since . I am using and ls compressor from a 5.3 truck . So I think your switch would be fine . Just fine tune your 134 charge to your system . I would try this first to see if it would work for you .
|
Re: AC Pressure Switch ?
Quote:
|
Re: AC Pressure Switch ?
After doing more research, I found that they make an all in one hi-lo Binary Switch.
They have different pressure ratings though. Some are rated at 28 off & 29 on low side, 400 off & 398 on hi side, & so on..... Would anyone know which one to get? I did look up the part number on the original switch to see if it was a hi-lo one. It just lists for low pressure. So, I'm thinking that there wasn't a hi pressure switch on these truck ac systems.. |
Re: AC Pressure Switch ?
R12 usually only had a LPCO.
Several AC hose and fitting vendors have liquid side fittings with Schraeder valves inside so the switches can be changed without evacuating the system. You may be able to get a head for the Sanden 508 that has provision for a HPCO switch... if not you can get braze in sections for the hard lines with an HPCO fitting as described above. The latter is the route I took. HPCO is installed near the high side gauge port on my 76. You definitely can get a 7 piston Sanden 508 compressor head machined for the same line fittings as the 1983 Harrison R4. https://www.ebay.com/itm/Dirty-Dingo...-/191979228686 The Third Gen F-Body guys have a lot of info on this kind of conversion. https://www.thirdgen.org/forums/cool...e-systems.html If you want an engineers perspective look at the E38 BMW boards... the Corvette boards are a friendlier crowd and full of engineers too. |
Re: AC Pressure Switch ?
Quote:
Old thread, but would it be possible to replace the factory LCO swith with an aftermarket Binary switch from Vintage air? EDIT: Is the switch in the accumulator already abinary switch??? |
Re: AC Pressure Switch ?
Quote:
Post is old, but.. Jesus christ, the all in one sensor. The hi lo pressure savior switch... Low side sees 35 psi... High side sees 250... If your have this unicorn sensor installed on the low side and sees 250psi, you have more problems than you think.. |
Re: AC Pressure Switch ?
Quote:
|
Re: AC Pressure Switch ?
Quote:
Quote:
|
Re: AC Pressure Switch ?
Quote:
For me currently I am trying to convert my 74 C10 to a different form of clutch control. I converted to R134a years ago and the system worked but after letting the truck sit while redoing the engine the refrigerant leaked out. I refilled the system again but was having issues with the main inline fuse that kept turning the blower motor off and I believe freezing up the evaporator, at that the capillary cycle switch would shut the compressor down. So I am trying to use a low pressure switch from a later truck or GM car to control the compressor but I am concerned that the R12 might not have the adjustment range needed. |
Re: AC Pressure Switch ?
Quote:
|
Re: AC Pressure Switch ?
I ended up finding a low pressure cycle switch from a 1985 that is made for R134a. The Murray number is 36674.
|
Re: AC Pressure Switch ?
I just want to follow up with the solution to my problem. I had my three wire pressure sensor after the orifice tube/expansion valve. I didn't think through this setup enough to realize that all the vintage air setups I have installed, have an expansion valve inside the cab and the OBS trucks have the orifice tube on the outlet of the condenser. I moved the sensor to the correct position and everything works perfectly now. Lesson learned. I draw my systems out now prior to ordering fittings or making lines.
|
All times are GMT -4. The time now is 06:04 PM. |
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com