Originally Posted by wwest (Post 6883355)

Is it even possible to fully, properly, charge the system

Originally Posted by Dublinoh (Post 6883327)

My new to me 1987 911 has poor AC function and PO told me "it just needs a charge". It has the r134 hardware and I was told it was converted...but not sure with what.

Today a Valvoline oil change shop tested the charge and it was low and is apparently r134. Hooked it up to a recharge machine...which pulls a vacuum of 29.2 HG and it passes the leak test. Mechanic computes that the system should take 1.1 Kg of r134. We are hooked up on the high and low side the engine not running. Machine is able to get .54 Kg of refrigerant in then tells us the charge has failed. So now we start it up, it blows about 60 at the vent...he says "sorry maybe there is a blockage some where"...no charge for the service. The pressure is higher than before we started, temp 81 humidity 50%.

Comments???

Originally Posted by Scott R (Post 6883411)

Yes, for example:

Recovery System - CoolTech Multi-Refrigerant ROB17800B

Never had to run the engine to charge in the shop, only to test it in the end. Recover, flush and recharge are handled by one machine. The newest machines measure and tell you the oil charge and the refrigerant charge and type.

I don't know which particular machine they are using at this store, however "charge failed" a lot of times was the systems inability to handle a high pressure charge test. That would be a cycle when the machine runs up a charge pressure of the 300PSI to see if it's stable.

The other condition is blockage to the return service port during the charge. Something like a stuck expansion valve or bad internals in the compressor or contamination blockage in the system.

Sorry, these are just guesses since it's hard to say what in particular their machine is testing for.

Originally Posted by Dublinoh (Post 6883523)

It seemed like it failed because it could not get enough r134 in the system. Highest pressure I saw was something like 250/70. Would it make sense to get a can of r134 and the proper pressure gauge and try to charge from the low side alone?

Originally Posted by kuehl (Post 6883574)

The shop miscalculated the estimated R134a charge, you noted 1.1 kg which equals 38.8 oz(avdp); and its better to charge by weights of grams or ounces.

For a 1987 you should be starting off with approximately 39 oz or 1105 grams.
Then check pressures based on a P&T chart and ideally get closer to 43 oz or 1220 grams provided you are in the range of the P&T.

If they could only get .54 kg in then likely the refrigerant canister is colder than the ambient air temp or they have air in the system.

When you check your pressures:
1) Car in park, neutral, E brake on. Engine running. Windows up.
2) Thermostat set to max cold. Evap fan speed set to speed 2.
3) The engine deck lid should down, resting on the hoses.
4) Insure the front condenser blower motor is running.

If you want to report back to the forum with new results please provide:
A) Outside ambient air temp around the car at the time of the test.
B) At idle low and high side pressures.
C) Amount of refrigerant put in the system. (make sure they use virgin
and not recycled).

If by chance you go over this information with your ac tech and they 'just don't get it'... find another.

Originally Posted by wgirardot (Post 6883598)

Griff,

how many ounces R134a for an '82 SC (intitial charge) ?

Originally Posted by Scott R (Post 6883555)

You could, but if it were me I would check the balance of the rest of the system.

Originally Posted by kuehl (Post 6883574)

The shop miscalculated the estimated R134a charge, you noted 1.1 kg which equals 38.8 oz(avdp); and its better to charge by weights of grams or ounces.

For a 1987 you should be starting off with approximately 39 oz or 1105 grams.
Then check pressures based on a P&T chart and ideally get closer to 43 oz or 1220 grams provided you are in the range of the P&T.

If they could only get .54 kg in then likely the refrigerant canister is colder than the ambient air temp or they have air in the system.

When you check your pressures:
1) Car in park, neutral, E brake on. Engine running. Windows up.
2) Thermostat set to max cold. Evap fan speed set to speed 2.
3) The engine deck lid should down, resting on the hoses.
4) Insure the front condenser blower motor is running.



If you want to report back to the forum with new results please provide:
A) Outside ambient air temp around the car at the time of the test.
B) At idle low and high side pressures.
C) Amount of refrigerant put in the system. (make sure they use virgin
and not recycled).

If by chance you go over this information with your ac tech and they 'just don't get it'... find another.

Originally Posted by Dublinoh (Post 6883720)

This morning: temp 81 humidity 50%
thermo max/ fan also max (not at 2) /deck was open and with engine not running car would take only take 20 oz
at idle with same conditions low side 28 high side 125

Originally Posted by kuehl (Post 6883574)

If by chance you go over this information with your ac tech and they 'just don't get it'... find another.

Originally Posted by kuehl (Post 6883977)

When testing pressures with engine running:
DECK LID DOWN, DECK LID DOWN, DECK LID DOWN


When testing pressures:
ENGINE RUNNING, COMPRESSOR CLUTCH TURNING, ENGINE RUNNING, COMPRESSOR CLUTCH TURNING,ENGINE RUNNING, COMPRESSOR CLUTCH TURNING

Originally Posted by Bob Kontak (Post 6883922)

Dublinoh - did you ever have the pressures tested with the motor running?

You can always go to the parts store and buy a can of R134 with a gauge on it. Yes, they are cheesy but I sure would like to see you try charging your system with the system running.

Originally Posted by Dublinoh (Post 6884046)

I get "deck lid down"...this info is unfortunately after the fact. I am trying to report the data I have now. So any pressures measured with the deck lid up are not diagnostic? My compressor clutch looked like it was turning...is that not the case?