7 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHDiagnosing AC pressures, opinions?
Reported or suspected cause
(worn cylinders
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Read evidence and context
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Leading evidence: '(worn cylinders' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is '(worn cylinders' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check fuses and they seem ok), would you agree' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion · Original poster
I think these readings - high LP, Low HP- indicate a bad compressor ( I checked the fuses and they seem ok), would you agree?
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Suggestion
You could also pull the wire on the AC compressor and check its resistance to ground, it's going to be about 2-10 ohms I would guess.
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Suggestion
If it is not working, I would check the wiring diagram and figure out what it takes to energize the compressor.
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Suggestion
If this is true you will want to inspect the refrigerant
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I hooked up the manifold gauges and see the pressures shown below. This was after warming the car up and turning on the Air to high and full fans. I think these readings - high LP, Low HP- indicate a bad compressor ( I checked the fuses and they seem ok), would you agree?
Thanks
Considering the pressure it equal on both sides, the compressor is doing no work.
You need to be more specific regarding your symptoms. I would say that you most likely have enough pressure in the system for it to turn the compressor on, but you don't say if the compressor is on in the HVAC control, or if the AC is working on not.
If it is not working, I would check the wiring diagram and figure out what it takes to energize the compressor. I'm going to say it requires the following:
- Low pressure switch closed (check the resistance across the switch, should be less than 1 ohm)
- HVAC head unit see this, and applies 12 VDC signal to compressor clutch, most likely through a relay.
You could always jump 12 VDC to the compressor to see if it work and starts making cold air.
You could also pull the wire on the AC compressor and check its resistance to ground, it's going to be about 2-10 ohms I would guess. If you have an open circuit, the clutch electrical circuit could be at fault.
Should be pretty easy to troubleshoot.
Attached find a couple of pages from my 996 Turbo reference that gives you some temp vs. pressure callouts.
I suspect the 996 system has comparable numbers, though I make no guarantee of this.
"This was after warming the car up and turning on the Air to high and full fans."..
That sentence can be understood in 2 ways:
A) You took the gauge readings while or immediately after the compressor clutch was engaged.
B) You took the gauge readings sometime much after the compressor clutch was engaged,
say 10 minutes or more later.
Assuming you have both the red and blue service set
valves on your gauge set turned in CW (closed):
If the readings on the gauge in your first post are with the
engine turned off, system was sitting for awhile, then you
are reading static pressure.
If the readings are with the engine running, compressor
clutch is engaged and the outer hub of the compressor
clutch is turning in unison with the clutch pulley....
then your compressor is suspect (worn cylinders
and or non closing reed valves).
If this is true you will want to inspect the refrigerant
oil for signs of debris (contamination, compressor parts,
filings, etc), if you find debris you will have to liquid
flush the entire system (you don't flush compressor's
driers or TEV's): condensers, ac lines, evap with TEV
removed, and replace the drier, ... before you toss
a new compressor on there.
Go back and repeat the pressure testing (compressor
running, clutch engaged, service set manifold valves
CW).
http://griffiths.com/product-categor...6-987-996-997/
Thanks for the input- and sorry for the incomplete description of the problem ( was rushing out the door at the time!).
Anyway- no cold air and the compress clutch never engages. I think I'll try to figure out if the compressor is getting power as suggested.
If the engine coolant is "tending" toward overheating, or the coolant temperature sensor is defective, the engine ECU will prevent the compressor clutch from engaging.
Also, an open OAT, Outside Air Temperature, Sensor will indicate -37dF, which will also disable the compressor.
OAT sensor... Little probe in the passenger side radiator inlet.
This is a source reference. Confirm exact model applicability in the original material.
