Intermittent A/C
 

I live in Charleston SC where the temp and humidity are usualy equal... c97 deg. F. The A/C will blow very cold at night, but barely works during the heat of the day.

There are no leaks, it has a proper charge, in the blue, there are no bubles through the sight glass, the compressor works, etc. etc. All seems well with the system, it was converted to RJ134 before I purchased it, but I just can't figure out why it will barely work during the heat of the day, but any other time it can freeze me out???

What to think?

Sincerely,
Tommy Darcy
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'82 300D (Turbo) c300k miles, "Mary."

How about the system is over charged...

The high side presssure is greater in the daytime. High pressure switch kicks in to prevent system damage.

??????? Can you use the sight glass for charge on a converted system???


Just an idea,

Michael

Charge
 

When I checked the charge I did so with a set of generic A/C pressure guages... the readings were right in the middle of the "blue" field, which should have been the optimal charge, not sure of the numbers c24 something. Although, I did this during the heat of the day... :confused:

Does anyone know what the pressure readings should be for the 300D's A/C system? Do you think that since the system performs perfectly at night, I should check the pressure at night and ensure the system registers the same numbers at noon?

I seriously thought about installing an inverter and using a Cruise-Aire through-the-hatch boat A/C... LOL. ;)

Sincerely,
Tommy Darcy
----------------
'82 300D (Turbo) c300k miles, "Mary."

The sight glass(if there is one) on 134 systems doesn't carry as much meaning as it does on an R12 system. 134 sight glass can appear foamy and be functioning just fine.

You need to hook up some 134 gauges and look at the pressures in the heat of the day. If you don't have the gauges, a shop should do it for an hrs. labor.

With the A/C system off the sight glass shows nothing... with the system on it shows a greyish foglike flow... I'm assuming that that is the RJ134 coolant, but I'm not sure.

Sincerely,
Tommy Darcy
----------------
'82 300D (Turbo) c300k miles, "Mary."

Without pressures and temperatures you are flying blind. You need to connect a manifold set and get the ambient temp and the vent temp. Post these four parameters here.

Since it works at night and not in the daytime it is most likely undercharged, but don't assume this without gauges and temps.

BTW, the high pressure switch does NOT turn off the a/c, it turns on the aux fan to bring down the high side pressure to prevent damage.

Good luck,

Right larry,

What high-side pressure should a convert system be charged to at 95-100F day?
NONE of my systems have been converted, so I am not aware.

Michael

You need a pressure/temperature chart for your car. For the MB's the service CD has the best ones. These vary widely from car to car.

Post your pressures and temperatures and we will try to find it for you.

Good luck,

O.K. I evacuated the a/c system to 24psi... no a/c.
I then pressurized the system to 35psi... nothing.
I then pressurized the system to 45psi... nada.
I then tweeked the pressure down to c37.5psi and it almost blows cold? :confused:

I find this whole situation unacceptable :mad:

High temps, heat indicies of over 110F can be dangerous, maybe I should look into a newer car, perhaps a rice burner.

expansion valve blockage?

I assume the 35psi/45psi are low pressure readings?

What about the readings on the high pressure side?

You CANNOT charge an a/c properly by monitoring low side pressures only!

You need Lo and Hi pressures and ambient and vent temps.

Don't you think it would be less expensive to seek some pro help with your a/c than to buy another car?

Good luck,

If a system is cooling very well at night , but not in the heat of a hot day, my suspect would be that you have NO aux fan engagement , thus the unchecked a/c high side pressures are cutting out the compressor..
That would be my first check going by what you have posted..
... again, Gauges on high side is where you should be looking

The aux fan does run, and I believe it is operating properly.

I spoke with the PO and I think my problem might be that the PO changed the system over to rj134... well, anyway he changed the ports and added some coolant, but the system was never flushed, etc. :eek:

I guess I'll have to take it to a shop to have them do it right, although it will probably be very expensive :pukeface:

Thanks for all the help

Go to Autozone and get the $8.99 AC repair DVD by Bruce Bone......I just watched it last night, 1 hr and very informative. it reiterates alot of the good info on this forum and he clearly shows/explains step by step.

In my area I am finding more and more shops do not know or care what they are doing and your better of to study, get some tools and DIY!