mystert

I looked over the Porsche R134a Conversion TSB and noticed that the 965 uses 1220g and the 964 uses 840g of refrigerant. All the system components are the same with the exception of the compressor. Is the added refrigerant due to the compressor or is it a typo?

griffiths

I would never say "typo" in a TSB, against all etiquette.

But. You are correct, all the components are identical with the exception of the pulley on the comp clutch.

Therefore, use the other lower suggested gram weight to start, 850 nominal, and then always check by P&T.

A914MAN

Update: my friend Tony was able to come by today and found the system wasn't as low as thought. He said it was about 1/2 low on refrigerant, based on the pressure in the system.

The PO said it had been over 2 years since he had added any refrigerant, so Tony felt as the system wasn't leaking badly so we added 14 oz of R12 and it's cooling pretty good. It's a busy day for me, so I haven't had a chance to compare ambient temps to output temps, but it is blowing cold.

Based on loosing a little oil during the charge process, Tony didn't think the oil had gotten scorched from running the system too low on charge (I only tried it once for about 2 mins). He said that many times you can tell when the oil has gotten too hot.

So for now, I'm hanging on to the R12 I have, the seal kit, new receiver/dryer, new expansion valve, and new quart of R12 mineral oil until it stops cooling, and then I'll dig into it.

If it's not broken, then I've got too many broken things to worry about

mystert

I picked up a chinese dual thermocouple thermometer. In a pot of boiling water it reads 212.2F, in a ice bath it reads 34.5F. At ambient temp the two thermocouples are .5F different. I went out and used it to take some readings on the AC system. I also ditched the Harbor Freight gauges and picked up a set of high quaity YellowJacket gauges. I removed the drivers rocker panel and front and rear inner fender liners to get access to the lines. Measurements were taken by clamping the thermocouple lead to the pipe. Measurements are as follows-


Ambient Temp 80F
Vent Temp 58-60F (taken with a different gauge/thermocouple that reads a 3-5F low.)

High Pressure 265psi= 151F Saturation Temp
Low Pressure 23psi= 25F Saturation Temp
Condenser Inlet= 178F
Condenser Outlet= 125F
Expansion Valve Inlet= 114F
Expansion Valve Outlet= 38F
Suction Line Rear Of Drivers Wheel Well= 40F
Suction Line Junction Under Door=43F
Suction Line Junction Above Rear Wheel/Cat= 78F
Suction Line After Rubber Hose Before Entering Compressor= 70F
Vent Temp= 60F

So far I have drained the oil from the compressor and junction below the door, replaced the receiver/dryer, replaced clogged condenser, replaced all O-rings w/green orings and nylog blue, replaced leaky expansion valve with JB weld on it, filled system with with 4.5oz of ester Oil as per Porsche TSB(3oz compressor, .5oz dryer, and 1oz condenser).

Subcooling= 265psi=151F, 151F-114F TXV Inlet Temp= 37F Subcooling OK
Evaporator Delta T= 114F-38F= 76F Delta T
SuperHeat= 25psi= 26F, Refrigerant Temp Entering Compressor Approx 75F, 75F-26F= 49F Superheat????? Should be 8-12F

Observation #1 - Condensation on suction line from evaporator to just before rear wheel well.
Observation #2 - When I remove low pressure gauge there looks to be oil/uv die in the schrader valve
Observation #3 - Previously Measured Delta T on dryer piping and it was 1F
Observation #4 - Previously found blockage in condenser by measuring temperatures at each row. Replaced it and did not check each row on the new condenser to see if it was clogged, assumed it is good.

I have done a lot of reading/research on HVAC over the past few weeks and I am stumped. Low Pressure on the suction side means a clogged system. It will not go higher than 25psi. From my temperature readings today, I dont see any major temperature changes that would indicate a clog but I am not a professional HVAC guy, just an Mechanical Engineer/Mechanic/Hardcore DIYer. Any ideas? Clogged/swollen low pressure rubber hose in engine compartment?

A914MAN

I too have gotten schooled on 964 A/C Eric.

I don't have gauges, which is why I didn't start taking stuff apart, which has worked out so far.

Would a leaking evaporator (my biggest concern) hold a half charge? There's no oil coming out the drain in the front, which gave me a little hope.

mystert

You can borrow gauges and a vacuum pump from Autozone here in CA and I bought a budget leak detector off Amazon to sniff my lines. Without the gauges you cant see the inner workings of the system to know if there is a problem. You could recharge your system with R134a with UV die to find a leak. If it was the evaporator you would see the die in the condensate drain with the proper lighting.

mojorizing

Eric, those Liquid Line temps are the suction line temps going to the compressor, correct?
Did you look at the sight glass on the top of the drier? any bubbles?

If you got a clog, the clog would act like an expansion valve and you'd have cooling going on down stream of the blockage.

mystert

Yes the temps are on the large diameter suction line that runs from the evaporator to the compressor. I edited the post to say suction line. While doing research I read that when converting R12 to R134a systems you should not use the sight glass to fill the system. Is this correct? It shouldn't matter what refrigerant you are using, when the refrigerant exits the condenser it should be a subcooled liquid with no bubbles. I didn't look at it, its a bit hard to see on our cars. Ill get the mirror and flashlight out after work and take a peek.


edit- Did more reading and you don't use the sight glass with R134a because the oil doesn't mix the same as mineral oil did with R12. It foams and clouds up, making the sight glass difficult to use.

mojorizing

The degree of bubbles in the sight glass is a visual way to see if it's fully charged or under charged, not to be used solely as an indication.

Did you go back with the correct oil? The car uses a low viscosity oil (PAG 46 equivalent, IIRC)

Looking at your numbers and comparing to mine. I know I'm low since the install of the new evaporator/expansion valve a month ago. I got 800g of 134A plus or minus.

80 deg ambient, full recirc, fan speed 2, vent goes to 55F within 5 minutes. Highside temp. at compressor is 113F, Liquid side of expansion valve is damn near ambient. I can feel the heat being removed from the condenser by the fan. Suction side of compressor is 53F. Big difference to your numbers.

Your condenser has a nice big delta T. I wonder if your expansion valve isn't stroking all the way?


edit....just took a drive and the vent goes to 42F with 88F ambient

A914MAN

90 here yesterday and cooling good.