AC pressure question with r12

[hdff]

What should the pressures be with a correctly filled system of r12? I put in the correct amount according to the manual but it is only about 70* at the vents. the gauges show 26 on the low side and 265 on the high side at 2000 rpms. what are the correct pressures ? about the system new evap. condenser dryer & hoses. remanufactured compressor. just trying to get it right

[gable74]

Originally Posted by hdff

What should the pressures be with a correctly filled system of r12? I put in the correct amount according to the manual but it is only about 70* at the vents. the gauges show 26 on the low side and 265 on the high side at 2000 rpms. what are the correct pressures ? about the system new evap. condenser dryer & hoses. remanufactured compressor. just trying to get it right

Pretty sure it depends on your altitude but 26 seems low to me. Mine at full charge was 30 on the low and 225 on the high. The manual has good info on the correct charging procedures and pressures. It available for download on the forum.

[hdff]

Originally Posted by gable74

Pretty sure it depends on your altitude but 26 seems low to me. Mine at full charge was 30 on the low and 225 on the high. The manual has good info on the correct charging procedures and pressures. It available for download on the forum.

Pasadena texas is i'm sure like Pasadena Maryland about 20 feet above sea level. hum wonder why my low is lower than yours and my high is higher at this point. since I don't know a whole lot about ac's, is that normal???

[gable74]

Originally Posted by hdff

Pasadena texas is i'm sure like Pasadena Maryland about 20 feet above sea level. hum wonder why my low is lower than yours and my high is higher at this point. since I don't know a whole lot about ac's, is that normal???

Again, Im not an expert...lol, but I believe low readings on the low side would usually be a result of the orifice tube being dirty. Pretty sure that tube being restricted can cause higher readings on the high side too. Maybe replace the orifice tube and since you are opening the system anyway....replace the dryer and expansion valve. Vacuum it down and recharge it. That's what I did anyway.

[hdff]

Originally Posted by gable74

Again, Im not an expert...lol, but I believe low readings on the low side would usually be a result of the orifice tube being dirty. Pretty sure that tube being restricted can cause higher readings on the high side too. Maybe replace the orifice tube and since you are opening the system anyway....replace the dryer and expansion valve. Vacuum it down and recharge it. That's what I did anyway.

that's not what I want to hear... lol I wasn't planning on opening it again. I had the evap box sent off and the poa expansion valve checked by a guy that refurbs ac units and I didn't take it apart when I got it back. he changed the evap core(new) while he had it apart. i'm not even sure I know where the orifice tube is....... I put on a new dryer, hoses, condenser and the compressor was new re manufactured. crap I hope it is something else and I don't have to take it apart........

[gable74]

Originally Posted by hdff

that's not what I want to hear... lol I wasn't planning on opening it again. I had the evap box sent off and the poa expansion valve checked by a guy that refurbs ac units and I didn't take it apart when I got it back. he changed the evap core(new) while he had it apart. i'm not even sure I know where the orifice tube is....... I put on a new dryer, hoses, condenser and the compressor was new re manufactured. crap I hope it is something else and I don't have to take it apart........

Me too, im no expert by any stretch so hopefully its something else.

[SJLenz1340]

When assembling the system was it purged with nitrogen and evacuated to at least 100 microns? If not then the non condensables would account for the high head pressures. Need this info before moving forward.

[Shade]

Sounds like either air in the system or a restriction somewhere. Might be a combination of things but you would not expect to see 265 psi (160F) on the high side unless it was really hot outside or the condensing coil was not getting air flow. 26 psi # is 27 degrees on the evaporator coil, check out a R12 PT chart. With a 27 degree coil you should have cold air. The elevation has nothing to do with the pressure of a refrigeration system. Like SJLenz is getting to, the most important question, did you pull a vacuum before charging the system with refrigerant?

[gable74]

Originally Posted by Shade

The elevation has nothing to do with the pressure of a refrigeration system.

According to the GM service manual it does. The POA is where the low readings are taken i'm pretty certain.

[davischevy]

Are you sure the heat/air diverter door is adjusted, or is closing? Is the valve in the heater hose working?

[hdff]

Originally Posted by davischevy

Are you sure the heat/air diverter door is adjusted, or is closing? Is the valve in the heater hose working?

I have a manual valve in the heater hose that is closed
It was pressured up with N2 and a vacuum was pulled but the on the first can which was oil the part that pierces the top of the can broke so we had to stop and it was a few days before I got the freon in, so that may be where I screwed up. The AC guy that refurbished and rebuild the poa called me and we talked for a while about it. I'm going to talk to some old ac guys at a shop near me. But a transmission problem came up this weekend that I need to address before I can drive it over there

[gable74]

Originally Posted by hdff

I have a manual valve in the heater hose that is closed
It was pressured up with N2 and a vacuum was pulled but the on the first can which was oil the part that pierces the top of the can broke so we had to stop and it was a few days before I got the freon in, so that may be where I screwed up. The AC guy that refurbished and rebuild the poa called me and we talked for a while about it. I'm going to talk to some old ac guys at a shop near me. But a transmission problem came up this weekend that I need to address before I can drive it over there

Sounds like you may want to change the POA (restriction issues?), vacuum it down again, and recharge.

I would let it sit in vacuum for at least 4hrs to verify everything is good. I let mine sit in vacuum over night. I did not charge mine with N because I did not have access to it, but you can if you like.

Good luck!

[Eddie H.]

This system doesn't use an orifice tube. It has a Thermostatic expansion valve which has a small screen in the inlet that can get plugged up causing problems. If you haven't replaced it, that would be a good place to start.

[davischevy]

I agree with pretty much everything that has been suggested, but don't forget, if that diverter door that changes from heater to air conditioning, is not letting air blow across the evaporator it will throw all readings off.

Have you checked temps at the back side of the POA valve, and below the expansion valve?

[Eddie H.]

Yep, the blend air door has to be working properly, or it will never cool like it is supposed to. It has to block off the flow or air through the heater core and divert it through the evaporator core. Loosen the temperature control cable and move the door manually to make sure it is working right.

[gable74]

Originally Posted by Eddie H.

This system doesn't use an orifice tube. It has a Thermostatic expansion valve which has a small screen in the inlet that can get plugged up causing problems. If you haven't replaced it, that would be a good place to start.

That's what I meant... Change the expansion valve, vacuum it down, and recharge.