Do these look like normal R12 vent temperatures? - PeachParts Mercedes-Benz Forum

ps2cho · #1 08-13-2010, 03:11 PM

Been almost 2 months since my Evaporator + R12 'back'-conversion...everything seems to be running great. This is on my 87 260E.

Ambient today here in Phoenix is 108F.

Fast idle (1500RPM) I am getting ~60F from vents
Driving (~2100RPM) I am getting ~50F from vents.

Does this seem about right for r12?

Reason I ask is that on days like this, the car's ambient struggles to stay cool. It is 'comfortable', but not cold.

Is this simply the limitations of the A/C system on the 124's? I already know it is relatively small, but just curious.

samiam44 · #2 08-13-2010, 03:53 PM

it's possible...

What are your pressures. Both should be taken with system @ steady state: 1500-2000 rpm, max a/c windows down or doors open. Fan clutch should be roaring etc.
I would expect at 108F, to see 35-42 psi low side and 300-325 high side.

Have you measured the thermocouple resistance which is the trigger for the cycling clutch?? MB set those high- 42F or better. You can add a shunt resistor and bring it down effectively to 37-38F and see a lower vent temp.

Did you replace the compressor? How much mineral oil did you put back in the system? What does the site glass look like? Over charged or too much oil can be have similar to your situation. You should see a wisp of light bubbles as expansion valve opens and closes due to the change in pressure.

?? 87 does that have the 15cc compressor or the 17 cc? I think it's the smaller.

Michael

ps2cho · #3 08-13-2010, 05:29 PM

Compressor has been replaced with a remanufactured fourseasons one....Nobody ever stamped it, but it was replaced between 1999-2003

The clutch definitely is not cycling...I would guess with A/C on I lose about 20% of power, so its always obvious when it is on or off.

Don't have my gauges with me since I moved here, but will purchase some soon online since you can't find R12 anywhere local.

With the system completely evacuated, I put in 3x12oz cans...so 36oz. 36oz = 2.25lbs of r12.
I put the correct 90cm^3 of oil as stated in the manual.

I will check the site glass later today and see.

tjts1 · #4 08-13-2010, 05:41 PM

Just needs a recharge.

samiam44 · #5 08-13-2010, 06:27 PM

Hey,

You can pickup a cheap set of gauges online or even Harbor freight. The R134a cheapos are universal with "adaptor fittings" for the ends. Don't like that they have 2 valves instead of 3. Nice to blow any oil from the high side hose back through...
Site glass is your best tool without gauges. Also temp of the low side line- Got a IR thermometer? You can measure the temp on each line and it will be close(yea I know it will be off a bit for super heat).

look at a pressure/temp chart www.ackits.com/aacf/ptchart.cfm should get you there. @ 105F, coil temp should be 29F and high pressure 240-290psi. 110F, coil @ 32 PSi.
Now compare it to R134a: 110F, coil temp of 65F !!!! yea... that's why R-12 kicks butt in hot weather.

Michael

ps2cho · #6 08-13-2010, 08:14 PM

Just checked out R/D and there are definitely bubbles....
I put in the amount of R12 the Factory manual specifies, so sounds to me like the refridgerant level is OK.
Are my vent temperatures normal for that ambient or too high? If I hold my IR Thermo at the same place for 2-3 minutes it drops to 40F while moving, but I figured that is not accurate...right? Same with idle...holding @ the same position for a while will drop close to 50F, but sounds too 'cool' for correct temp.

So the Harbor Freight 134a gauge set will work for R12?
http://www.harborfreight.com/a-c-manifold-gauge-set-92649.html
The manual specifically says DO NOT USE for R12

What do you mean by coil?