Model: 911 Carrera
Engine Size: 3.2 lite
Refrigerant Type: r134a
Ambient Temp: 70
Pressure Low: 350+
Pressure High: 30
Country of Origin: United States
A friend converted his '86 Porsche 911 to 134a after having a non-working r12 system for many years, and asked me to charge it for him. This system has the compressor in the rear which feeds a condenser, and then there is a long run to the nose of the car to a second smaller condenser, which then feeds a drier, then the expansion valve and evaporator, finally returning back to the compressor in the rear. He bought a kit which replaced everything except the small secondary condenser in the nose. He did not flush this condenser out, and brought the car to me completely assembled. He didn't want to unplumb the condenser to flush it, but said instead he had gravity-drained it. Against my better judgement I agreed to give it a shot. I pressure tested the system with nitrogen, and it held overnight, so I vacuumed it and it held at -30 on my gauge overnight. The next morning I filled the system with 6 oz of ester oil in the low-side port, spinning the compressor manually to distribute the oil. I got one 12 oz can of r134a with the vacuume alone, and then started the car. The problem was that the low-side pressure was very high, and as we added a second can of 134a the low-side pressure rose to the top of the scale while the high-side stayed low. I suspected a block somewhere in the system, probably in the front condenser that I had not flushed. After evacuating the system we pulled the condenser and back-flushed it with mineral spirits and compressed air, and it did indeed have a block, which finally released in a gush of flush. I flushed about a quart of mineral spirits though the tube-and-fin condenser in both directions, then blew air through it for 10' until we could no longer smell the mineral spirits. Normally, I'd let this part sit overnight to evaporate anything else leftover, but we were in a hurry and reinstalled the condenser.
I pressure-tested the system with nitrogen again, and it passed. However, when I pull a vacuum I can't get down to -30 on my gauges. I pulled the vacuum for 5 hours and got to -15, then closed the valves on the gauges and let it sit overnight. I didn't lose any vacuum, but I'm disturbed as to why I can't pull down to -30 again.
Test your pump and gauges by pulling vacuum just on the manifold set, with it not connected to a car.
Excessive pressure also occurs because the condenser fans don't work. Were both fans working?
Edited: Wed July 30, 2014 at 9:45 AM by mk378
I'm not sure if one would see this on an analog gauge but I use a micron which is much more sensitive.
You have to watch the pump shut down sequence, pumping down on a system more that's still under a vacuum because as I have learned, you can pull the pump oil into your hoses, etc. This raises havoc with micron gauge reading but I'm unsure what it would do to a less sensitive analog gauge. You can open both valves on your gauge set while letting the hoses hang open to see if any oil comes out.
Thanks for all the good suggestions. I mis-typed when I said I checked the pressure with the manifold gauges closed, what I meant was that the ends of the hoses were closed from system (and removed), and I was measuring the pump alone. I checked with Robinaire, and their Tech support said it sounded like the pump went bad. The good news is that the pump was still under warranty and a replacement will arrive today. I suppose the bad news is that it required a replacement in the first place, after only 4 uses in 11 months.
Okay, I am officially confused now. New pump, and I still only get down to -15 on the Mastercool manifolds. These are the aluminum analog set, and I get this reading even with the gauges disconnected from the a/c ports with both valves on the manifold open. This should be pumping against the manifold alone, and I would have suspected I'd see -30 on the gauge. I can't find any info on the Mastercool website, and their tech line is closed. Any thoughts on trouble-shooting a gauge set?
First a couple of obvious things:
Pump must contain the proper amount of fresh oil and be placed on a level surface.
If the pump has multiple inlet fittings, the ones you aren't using must have air-tight caps.
If the car couplers have a knob on the top, the knob needs to be turned counter-clockwise to close off the valve in the coupler.
Pump down to -15 then close the valve on the pump and watch if the manifold leaks up. If it is leaking, only open one manifold valve at a time and switch the hoses around to try and isolate the leak.
Put the red or blue hose directly onto the pump if the fittings allow that-- then you could close off the yellow hose and the center part of the mainfold. If the car couplers don't match the pump, you could temporarily put a 134a conversion adapter on the 1/4 flare inlet on the pump.
Edited: Thu July 31, 2014 at 7:20 PM by mk378
Get intimate with your manifold set, hoses, and the pump!
1)Remove the blue and red hoses from the vehicle and the gauge manifold.
2) Close the manifold gauges.
Check the Yellow hose, low side gauge and valve, and the pump.
3) Hookup the yellow hose to the pump and move the other end to the low side gauge fitting (blue).
4) Run the pump and watch the blue gauge. If all is well it should go close to 30 inch vacuum mark. If not, you've isolated a problem with the pump, low side valve or the yellow hose leaking.
5) )Text IF you have a pump side valve close it and shut the pump off and see if the vacuum bleeds off.
6).IF NO PUMP VALVE then loosen the yellow hose at the manifold to bleed off the vacuum and THEN shut off the pump. This procedure will prevent sucking pump oil into the yellow hose.
7) So far so good! Looks like the low pressure gauge, low pressure manifold valve, pump, and yellow hose are OK.
Check the BLUE hose.
8) Remove the yellow hose from the low pressure manifold fitting and put it back on the center fitting.
9) Hook the blue hose to the low pressure manifold fitting. Make sure the port connector knob on the other end (if you have one there) is full CCW (closed).
10) Fully open the low side manifold valve.
11)Run the pump and watch the blue gauge. If all is well it should again go close to 30 inch vacuum mark. If not, you've isolated a problem to the low side manifold valve or the blue hose is leaking.
Check the RED hose. Same procedure as the blue hose.
12) Remove the blue hose from the low pressure manifold fitting.
13) Hook up the red hose on the same low pressure fitting. Same check with the red hose port connector closed.
14) Run the pump and watch the blue gauge. If all is well it should again go close to 30 inch vacuum mark. If not, you've isolated a problem to the red hose is leaking.
If all is well this far, one thing left to check.
Check the high side manifold valve.
15) Close the low side manifold valve.
16) Fully open the high side manifold valve.
17) Hook a tested good hose to the HIGH side manifold fitting.
18) Once more, run the pump and watch the red gauge. If all is well it should again go below zero (no gauge marks) to indicate the vacuum. If not, you've isolated a problem to a leaky high side manifold valve.
19) Hope you get here with no problems!
Sometimes you must accept things at faith value!
Thanks again for all the detailed help. I drained the hoses overnight, and a little bit of oil dribble out. When I went through the test that AC_Doc recommended, the gauge failed every time, so I think I've found the culprit. Is there anything I can do to rescue the manifold gauge?
Got all my gauges and pump sorted out, pulled a good vacuum and I've still got the same problem with the car. Put in one can of 134a and it looks okay, both high and low sides start to rise. Start the car to put in a second can, and the low side jumps to 300, while the high side drops to zero. I'm stumped for the moment. Any suggestions?
Sometimes you must accept things at faith value!
ZERO (or maybe a slight vacuum) on the low side tends to indicate you have a blockage on the low side. The low side has been sucked dry by the compressor.
All the refrigerant is compressed between the compressor and the high side of the blockage.
First MOST likely is the metering device (TXV valve or block) is closed off.
Second would be a blockage in the condenser.
Third less likely is a blockage in the line between the condenser and the TXV.
Sometimes you must accept things at faith value!
If you really have 300 on the LOW side, you must have the compressor connected backwards, so it's pumping out of the condenser and into the evaporator. Or the compressor is the wrong one for this application and it is rotating backwards-- a few types of compressors might pump backwards if rotated backwards, at least for a few seconds until they self-destruct.
Installing the compressor backawards is usually designed to be "idiot proof" but older stuff sometimes has the same fittings on both ports so it is possible. The port marked "S" (suction) is the low side and "D" (discharge) is the high side. You can test this with the compressor disconnected by turning it by hand (the same direction the engine turns it) to make it pump air.
Edited: Sat August 02, 2014 at 10:43 AM by mk378
The problem turned out to be that the low-side and high-side access ports were reversed. On the Porsche 911, the ports attach to a manifold that bolts directly to the Denso compressor. There is a top manifold that is fed from the evaporator with a hose that has a 45 degree bend, and a lower manifold that sends compressed gas to the condenser that has a hose fitting with a 90 degree bend (see pic). My friend made what seems to be a reasonable assumption, that the port for the low side should be attached to the upper inlet manifold (from evaporator), and that the high side should be on the lower manifold that feeds the condenser. However, when we switched the ports to what is shown in the attached pic, the system filled as normal. When I took the manifolds off the compressor I found two holes, one that connected to the system and one to the access port. So to my mind the upper access port should be seeing the low-side input, but I am clearly wrong, as it worked just fine when we switched the ports. So I'm not sure why it worked, but my friend is now happy.
Edited: Sun August 03, 2014 at 10:37 AM by idickers
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