Some A/C advice needed -- leaking valve stem - Page 2 - PeachParts Mercedes-Benz Forum

ps2cho · #16 08-04-2011, 08:17 PM

Something weird is going on....

Like I said, I just evaced to -27inHg for 1hr.

I just put in 1x 12oz can and my pressures are:
static 75psi
low: 45psi
high: 250psi

I'm lost

How could I be 250psi (it was going over 300psi until aux fan kicked on and brought it down to 250psi) be achieved with ONE 12oz can? Am I missing something here?

boneheaddoctor · #17 08-04-2011, 08:23 PM

Maybe its colder out now that it was at that time.....pressures fluctuate with temperature.

What are the vent temps getting down to? and what is the ambient temp in front of the car right now?

Matt L · #18 08-04-2011, 08:30 PM

Could you have introduced air into the system, when switching from the vacuum pump to the refrigerant can? That's the most likely cause of such high pressure with an undercharged system.

Even air in the line on the can is enough to cause trouble. I like to have the refrigerant supply hooked up but valve shut off, when evacuating the system. It also helps to have another valve for the hose to the vacuum pump, so it does not fill with liquid refrigerant. Turn off the (top) vacuum valve, then immediately turn on the refrigerant supply valve. That way you get no air from swapping fittings.

If you connect a spud fitting with vacuum in the line, you WILL suck in air.

ps2cho · #19 08-06-2011, 10:30 PM

So I have another question -- went to check static pressures today, and the High and Low side were different values?

Isn't that not normal? With the car off, shouldn't pressure be equal between both sides?

Ambient Temp: 105F -- Idle + aux fan blowing full speed
Static: I was getting 85psi low and 175psi high.

Running: 85psi low 290psi high (was reaching over 340psi before aux fan kicked on)

Seem right or?

Since the high side is getting really high, could my evaporator be overheating? Or is high side strictly condenser deal?

Matt L · #20 08-06-2011, 11:01 PM

The two sides will equalize after a while. If you checked after the car had been sitting overnight, suspect that your gauges are not accurate. Open the manifold valves if you want to ensure that you have the same pressure on both gauges.

vstech · #21 08-06-2011, 11:21 PM

... pressure sure should be equal, or close. no WAY it's off 90psi!!!
also, 27" is no where NEAR a deep enough vacuum to remove moisture from the system, or even to purge the air to get a good charge on the car.

also, with 1 can and air in the lines, you can easy get 200+ on the head. there will be no liquid to restrict flow, so pure compression will be showing on the manifold.

vstech · #22 08-06-2011, 11:23 PM

I gotta stress how important it is to get the correct volume of refrigerant into the car immediately after evacuation. charging from cans is a bad practice. cans are fine for topping the charge, but charging from evacuation with cans allows too much contaminants into the system. it can be done, but METICULOUS care is needed.

ps2cho · #23 08-06-2011, 11:32 PM

It was definitely unequal -- I could tell during removal of each quick connect and the pressure release between each port. The high side had a significantly larger hiss.

What could that mean?