A few A/C questions
05-13-2014, 01:34 PM
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A few A/C questions
1990 S2. About 6 years ago I had the A/C converted to R-134a from the original R-12. New compressor and lines were fitted at that time. System worked great. Since then, the mounting brackets on my compressor broke, and were not really repairable, so I purchased a new compressor and dryer (since everything was working fine, I didn't feel compelled to tear out the dash to replace the expansion valve). I had a shop evacuate the refrigerant prior to removing the old compressor. There was about a 10 minute period that the lines to the compressor were open, before I remembered to plug them up (!). Questions for you a/c gurus:
- The new compressor comes filled w/ oil. If I just fit new O-rings and old lines to the new compressor, will the a/c shop know how much oil the overall system needs? I know you're supposed to put in only as much oil as was in the old compressor, but I didn't capture that correctly upon removal.
-Did the a/c shop's evacuation pull any/most of the old oil out of the lines and condenser, etc.? Should I worry about too much old oil that may be left in the system reducing the life of the new compressor? Since they have to do an evacuation, again, to remove humidity, prior to adding refrigerant, do they then add more new oil? Obviously, I have no friggin' clue on this.
-Regarding the Service Manual specs about the a/c system (Section 87-42), what is transferrable about those from the R-12 to R134 refrigerant in terms of volumes and pressures - or can the a/c shop figure all that out w/o any guidance from the manual?
Thx, in advance!
- The new compressor comes filled w/ oil. If I just fit new O-rings and old lines to the new compressor, will the a/c shop know how much oil the overall system needs? I know you're supposed to put in only as much oil as was in the old compressor, but I didn't capture that correctly upon removal.
-Did the a/c shop's evacuation pull any/most of the old oil out of the lines and condenser, etc.? Should I worry about too much old oil that may be left in the system reducing the life of the new compressor? Since they have to do an evacuation, again, to remove humidity, prior to adding refrigerant, do they then add more new oil? Obviously, I have no friggin' clue on this.
-Regarding the Service Manual specs about the a/c system (Section 87-42), what is transferrable about those from the R-12 to R134 refrigerant in terms of volumes and pressures - or can the a/c shop figure all that out w/o any guidance from the manual?
Thx, in advance!
05-13-2014, 03:33 PM
#2
Rainman
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Let the compressor sit open overnight to drain all its oil out and put the PAG46 oil back in, about 6 oz is what it takes.
The vacuuming of the system for a long enough time should be OK to remove oil from the system.
R134 is charged to 75-80% of the R12 charge by weight...a late 944 is IIRC 36oz R12 so 28-30 oz of 134 is OK.
Expansion valve can be got at from under the hood on late 944.
The vacuuming of the system for a long enough time should be OK to remove oil from the system.
R134 is charged to 75-80% of the R12 charge by weight...a late 944 is IIRC 36oz R12 so 28-30 oz of 134 is OK.
Expansion valve can be got at from under the hood on late 944.
05-14-2014, 11:24 AM
#3
Yes and no. And you have other things to address:
1) Type of refrigerant oil. R12 used mineral oil. R134a can use either Ester or PAG. You can mix Ester with residual mineral oil however you want to avoid mixing Ester with PAG or PAG with mineral. Since the system was already converted you will to know what kind of oil was used during that previous procedure and use the same type. We have literally assisted in converting thousands of vehicles to R134a over the past 25 years. The factory suggests PAG46 weight, we use Ester100 weight without any issues.
2) If the system was bone dry (fresh) then the shop could just go by the factory specs for qty. But since the new compressor may have an unknown qty of oil, and there is residual oil in the other old components, there would be 'guess work' involved'. If the compressor is on the car and has have a drain plug located at lowest point on the compressor, remove the drain plug and capture the oil in a can, turn the outer clutch hub nut clockwise several times to help move the pistons and assist in the drain. Properly dispose of the oil.
If the compressor does not have a drain plug take the compressor and rest it over large can with the 2 hose manifold ports aiming in the can, ditto on turning the hub nut, turn the compressor in a few different directions to help with the draining. Based on what you have done so far, with all of the oil drained from the new compressor your system will need to have 4-5 total ounces of oil added during after the shop evacuates the system (pulls a vacuum) and prior to charging with refrigerant.
Vacuum does not suck out all of the oil, only gases. Any residual oil near the point of vacuum that is gravity fed will be pulled out. Too little oil is more of a concern than too much. Too little means less lubrication for the compressor leading to friction, heat and wear. Too much oil would reduce the heat transfer in the condenser and evaporator heat exchangers.
The shop you will have service the system WILL pull a vacuum prior to charging with refrigerant. Again, if you follow the suggestions on oil noted above you should be OK.
The amount of R134a refrigerant needed in the system is addressed in TSB 8717-9501. However, any 'experienced' ac tech knows that they can determine the proper charged based on "P&T" or pressures and temperatures.
1) Type of refrigerant oil. R12 used mineral oil. R134a can use either Ester or PAG. You can mix Ester with residual mineral oil however you want to avoid mixing Ester with PAG or PAG with mineral. Since the system was already converted you will to know what kind of oil was used during that previous procedure and use the same type. We have literally assisted in converting thousands of vehicles to R134a over the past 25 years. The factory suggests PAG46 weight, we use Ester100 weight without any issues.
2) If the system was bone dry (fresh) then the shop could just go by the factory specs for qty. But since the new compressor may have an unknown qty of oil, and there is residual oil in the other old components, there would be 'guess work' involved'. If the compressor is on the car and has have a drain plug located at lowest point on the compressor, remove the drain plug and capture the oil in a can, turn the outer clutch hub nut clockwise several times to help move the pistons and assist in the drain. Properly dispose of the oil.
If the compressor does not have a drain plug take the compressor and rest it over large can with the 2 hose manifold ports aiming in the can, ditto on turning the hub nut, turn the compressor in a few different directions to help with the draining. Based on what you have done so far, with all of the oil drained from the new compressor your system will need to have 4-5 total ounces of oil added during after the shop evacuates the system (pulls a vacuum) and prior to charging with refrigerant.
-Did the a/c shop's evacuation pull any/most of the old oil out of the lines and condenser, etc.? Should I worry about too much old oil that may be left in the system reducing the life of the new compressor? Since they have to do an evacuation, again, to remove humidity, prior to adding refrigerant, do they then add more new oil?
The shop you will have service the system WILL pull a vacuum prior to charging with refrigerant. Again, if you follow the suggestions on oil noted above you should be OK.
The amount of R134a refrigerant needed in the system is addressed in TSB 8717-9501. However, any 'experienced' ac tech knows that they can determine the proper charged based on "P&T" or pressures and temperatures.
05-14-2014, 11:41 AM
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Griffiths & V2 - many thanks...that info is very helpful and should get me back on the road shortly after the new mounting bolts arrive. Much appreciated.
05-20-2014, 09:18 AM
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Best laid plans...system evacuated, held vacuum perfectly, we got the right amount of PAG back in, and pressurized. All works well, system cools perfectly, EXCEPT, the compressor isn't cycling...it just stays on, and the low side will drop to 10 at > 2000 RPM, so we shut it down immediately. We put 29 oz in, and when it didn't cycle, the tech put 2 more oz in, but the compressor just wouldn't cycle off. The tech's recommendation was that the pressure switch in front of the dryer needed to be replaced, so we did an evac. I'm almost positive the switch was working before, so I'm suspicious of that. I thought it might be the compressor's shut-off electrical cable, since it was difficult to tell whether that spade went on correctly inside that stupid rectangular connector cover, but the tech said the clutch was turning on and off, so that couldn't be it. I guess I understood it wrong, but I thought the pressure switch would send pressure status to the ECU which would decide whether to cycle the compressor off; isn't that what the clutch on the compressor does? Anyway, now I need to dig out the wiring diagram, because apparently there's a low and a high pressure switch and a freeze switch, whatever that is, any of which could be causing the problem. I have to say, this is one area where the Clarks-Garage overview is lacking in detail. I should probably work on that when I get this figured out. Is it possible that 31 oz was not enough refrigerant to trigger the pressure switch? If I replace the pressure switch, will I have to replace the new dryer I just put in, again?
05-20-2014, 10:22 AM
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Rainman
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low pressure switch is about $6 and easy to replace
"freeze switch" is probably the temp-sensing coil by the evaporator, i dont think that would be bad...its just wires.
"freeze switch" is probably the temp-sensing coil by the evaporator, i dont think that would be bad...its just wires.
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05-30-2014, 02:02 AM
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OK AC gurus, looking at the S2e-diagram, there is no low pressure switch. There's a single pressure switch housing on the inlet side of the dryer (on the high pressure line), but it has either a) two sets of pressure transducers that are set to trigger at different pressures, or b) a single transducer that actually throws two switches at the same time (pressure, actually).
Either way, the switches perform different functions in the diagram. One cycles the compressor and the other triggers the fan relay to turn the fans on high. The one that cycles the compressor has a common junction w/ a line from the DME. So, I can't tell if the pressure switch actually triggers the compressor clutch, or if the DME does, or perhaps its either/or. I'm assuming the switch does, and the line to the DME just notifies the DME that the compressor is on...but that's a WAG.
There are six On/Off/BAR designations (from 2 BAR to 30 BAR [!]) that I cannot tell how they relate to the two, single pole switches. Maybe someone can enlighten me on that. If I do the math right, 30 BAR would be somewhere in the territory of 435 PSI. Wow! One more thing; if those designations describe the pressure at which the pressure switch is switched in, does the switched in position actually engage the clutch (turning on the compressor), or disengage it (turn it off)?
Since there is almost no available information in the SM, online search or in the forums about how this switch works, that supports my theory that it rarely fails. Plus, I don't want to just blindly replace a $120 switch if it's perfectly fine, just because some knucklehead at Pep Boys says so (I had them do the evac and recharge). But I can't do any real diagnosis on the system, until I know how it's really supposed to work.
OK, that's enough questions for now. Thx!
Either way, the switches perform different functions in the diagram. One cycles the compressor and the other triggers the fan relay to turn the fans on high. The one that cycles the compressor has a common junction w/ a line from the DME. So, I can't tell if the pressure switch actually triggers the compressor clutch, or if the DME does, or perhaps its either/or. I'm assuming the switch does, and the line to the DME just notifies the DME that the compressor is on...but that's a WAG.
There are six On/Off/BAR designations (from 2 BAR to 30 BAR [!]) that I cannot tell how they relate to the two, single pole switches. Maybe someone can enlighten me on that. If I do the math right, 30 BAR would be somewhere in the territory of 435 PSI. Wow! One more thing; if those designations describe the pressure at which the pressure switch is switched in, does the switched in position actually engage the clutch (turning on the compressor), or disengage it (turn it off)?
Since there is almost no available information in the SM, online search or in the forums about how this switch works, that supports my theory that it rarely fails. Plus, I don't want to just blindly replace a $120 switch if it's perfectly fine, just because some knucklehead at Pep Boys says so (I had them do the evac and recharge). But I can't do any real diagnosis on the system, until I know how it's really supposed to work.
OK, that's enough questions for now. Thx!
05-30-2014, 07:48 AM
#9
phfly- "what normal low pressure reading at R12 system?" -
Not quite sure what you mean.
If you are asking, what is the normal low side pressure of an R12 system when operating, the average is about 30 psi. But..... that does not mean everything is ok. You can have a 30 psi reading with a low or shortage of refrigerant charge as well as an overcharge or too much refrigerant. And the pressure reading typically relates to the temperature of the particular refrigerant coming out of the evaporator core.
Treiber
on a TEV/Drier system, as opposed to an Orifice Tube/Accumulator system:
2 bar or 29 psi can be assigned to the minimum pressure required for the clutch to engage; typically when pressures are less than 29 psi it is a sign that the system is low on refrigerant, a system low on refrigerant does not have the propensity to carry enough refrigerant oil to keep the compressor adequately lubricated (which leads to excessive friction, heat and grenades).
30 bar or 435 psi is usually assigned to the clutch cut-off;typically when pressures are near this high extreme a system risks the chance for blow outs (i.e. compressor nose seal), excessive heat (breakdown of refrigerant oil viscosity) leading to compressor wear or damage. 435 is not an ideal high side cut out, we use a much lower value.
A binary switch provides 3 functions: low side cut off, high side cut off and recovery. Typically binary switches are 2 wire switches, either the switch is on or off.
Not quite sure what you mean.
If you are asking, what is the normal low side pressure of an R12 system when operating, the average is about 30 psi. But..... that does not mean everything is ok. You can have a 30 psi reading with a low or shortage of refrigerant charge as well as an overcharge or too much refrigerant. And the pressure reading typically relates to the temperature of the particular refrigerant coming out of the evaporator core.
Treiber
on a TEV/Drier system, as opposed to an Orifice Tube/Accumulator system:
2 bar or 29 psi can be assigned to the minimum pressure required for the clutch to engage; typically when pressures are less than 29 psi it is a sign that the system is low on refrigerant, a system low on refrigerant does not have the propensity to carry enough refrigerant oil to keep the compressor adequately lubricated (which leads to excessive friction, heat and grenades).
30 bar or 435 psi is usually assigned to the clutch cut-off;typically when pressures are near this high extreme a system risks the chance for blow outs (i.e. compressor nose seal), excessive heat (breakdown of refrigerant oil viscosity) leading to compressor wear or damage. 435 is not an ideal high side cut out, we use a much lower value.
A binary switch provides 3 functions: low side cut off, high side cut off and recovery. Typically binary switches are 2 wire switches, either the switch is on or off.
05-30-2014, 10:11 AM
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Rainman
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the 944 switch is a 2-wire, on or off, and is a low-pressure switch.
cars after 87 also had a high pressure switch installed next to the LP switch.
the LP switch is less than $7 and takes less than 30 seconds to replace.
if the HP switch wasnt working, i dont think you'd ever know until the oem hoses burst or popped their fittings at 400+psi.
cars after 87 also had a high pressure switch installed next to the LP switch.
the LP switch is less than $7 and takes less than 30 seconds to replace.
if the HP switch wasnt working, i dont think you'd ever know until the oem hoses burst or popped their fittings at 400+psi.
05-30-2014, 11:13 AM
#11
the 944 switch is a 2-wire, on or off, and is a low-pressure switch.
cars after 87 also had a high pressure switch installed next to the LP switch.
the LP switch is less than $7 and takes less than 30 seconds to replace.
if the HP switch wasnt working, i dont think you'd ever know until the oem hoses burst or popped their fittings at 400+psi.
cars after 87 also had a high pressure switch installed next to the LP switch.
the LP switch is less than $7 and takes less than 30 seconds to replace.
if the HP switch wasnt working, i dont think you'd ever know until the oem hoses burst or popped their fittings at 400+psi.
05-30-2014, 12:52 PM
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Arominus is right. There is no low pressure switch (that I can find) on our S2's. Also, my compressor is coming on and working just fine. Temp is great at the vents etc.; its just that the compressor doesn't cycle off like its supposed to and I'm trying to figure out why that is. The low pressure line drops well below 20-30 psi mark. High pressure side range is normal.
06-01-2014, 05:20 PM
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So, to close this thread, it turns out the pressure switch was working fine, as I suspected. Apparently, I just didn't have good contact on the spade lug that connects the compressor to the pressure switch and DME, so after fixing that, cleaning a few other connections and relay contacts up, and re-pressurizing, everything worked fine. Pressures on both sides were right where they needed to be. And now I know a lot more about the A/C system.
Also, in reference to a question I asked earlier in this thread, I found this from 968turbos2 - "Idle speed motor makes up for the extra draw on the engine. Check the small wires on the top of the AC compressor and make sure it is plugged in. It sends a signal to the DME that the AC is on so when decelerating, the idle speed motor kicks in prior to the rpm dropping below 1100 or so to alleviate the dip on decal from the AC drag."
I don't know where/how you learn stuff like that, because the DME is just a mystery box w/ mystery logic to me, but this is awesome to know. Thx all, for your help!
Also, in reference to a question I asked earlier in this thread, I found this from 968turbos2 - "Idle speed motor makes up for the extra draw on the engine. Check the small wires on the top of the AC compressor and make sure it is plugged in. It sends a signal to the DME that the AC is on so when decelerating, the idle speed motor kicks in prior to the rpm dropping below 1100 or so to alleviate the dip on decal from the AC drag."
I don't know where/how you learn stuff like that, because the DME is just a mystery box w/ mystery logic to me, but this is awesome to know. Thx all, for your help!
06-01-2014, 05:42 PM
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Nice, glad it's working! Re the idle speed and the ECU, that's how pretty much every car made in the last 30+ years works 
Also make sure that you loosen the AC compressor mounts before trying to adjust the belt. Usually mounts get broken from people trying to adjust the belt tension by moving the compressor with the compressor mounts still tight.
Also make sure that you loosen the AC compressor mounts before trying to adjust the belt. Usually mounts get broken from people trying to adjust the belt tension by moving the compressor with the compressor mounts still tight.
06-01-2014, 10:21 PM
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Well, right, BikePilot...that's a great example of the intricate knowledge the pro's have, vs. those of us w/ more courage than sense. Everyone says, "jump on in, and learn how to DIY", which I think is great, but sometimes those basic items everyone in the biz takes for granted can trip us noobies up. 
As for how the brackets got broken, I'm pretty sure it happened just as you said. Not willing to share who might have been involved.
Live and learn. 
As for how the brackets got broken, I'm pretty sure it happened just as you said. Not willing to share who might have been involved.
Live and learn.