On a bone-stock factory A/C system, 1985 F-350 Diesel, with R134a conversion :

Engine fan is DIRECT DRIVE = no silly fan-clutch

A ball-cut-off valve is in the heater-hose.


Outside temperature of 89* American and very humid.



QUESTION: On a properly charged R134a system, what should the equalized HIGH- and LOW-side pressure reading be when engine OFF ??



Currently, my system shows 87-PSI with engine OFF.

Low-side at hi-idle is 44-PSI

High-side at hi-idle is 255-PSI

My A/C performance is very depressing with dash temps barely getting below 62* under the above conditions.

The drier/accumulator and the cool line are sweating, but they are not frosting over like a good working system does.

At the same time, my wife's 91 Dodge/Cummins is showing 30* dash temperature and will chill you to the bone.


I tried a $36 variable orifice valve and did not experience the dramatic results everyone was claiming.

Last summer, I replaced the drier/accumulator and installed a new standard-issue orifice, pulled an over-night vacuum, oiled, charged, and was getting 40-ish dash temps.


Surely, seeing as these are closed systems, there is an industry standard pressure recommendation one should see with a proper R134a charge when engine is OFF and the system pressure is equalized.


Thanks for reading.

 

I don't remember exactly but I think my truck showed a similar pressure (around 90 psi) with the system off when I had the system full with a standard orifice tube.

I have a fan clutch, 180F thermostat, variable orifice tube, and all the a/c components are new. It get's nice and cold running R134A. The accumulator doesn't frost but it get's cold enough that there is tons of condensation on it. Even the cool side of the compressor will have condensation on it. I put my R134A canister on a digital scale when filling my system. I am actually .4 lbs short at the moment, I had to replace the compressor and that is when I put the variable orifice in it.

I have no heater core shut-off and the little bit of insulation left on the blend door crumbles like dust when touched.

 

Have you checked the evap coil? Most of them get dirty over time, and when they sweat it turns to mud and clogs it up.

 

It has been about six months since I have seen the evaporater and it looked okay then and a couple years since it got a thorough BOTH SIDES cleaning.

The cab got to smelling like a pack of wet dogs anytime the A/C was ON and I found the evaporater completely plastered over with a thick wet mat of nasty gook; I don't see how there was any circulation at all.

That was over 20-years of accumulation.

I also removed about two buckets-full of leaves and trash from the blower-housing at that time, plus a couple more bucket-fulls from under the cowl and within the kick-panels, and from both sides of the heater-core box.

I glued and zip-tied a screen underneath the cowl slots and haven't found so much as a pine-needle in there since.






I have done a ton of reading and am sort of led to think a good flushing of the evaporater and condensor will be my next step.


In my way of thinking, I believe knowing the engine-OFF equalized pressure of a properly charged system is right up there in importance with knowing the total ounces necessary to fill an empty system.

Armed with this information, one would have a reasonable idea whether the pressure charge is within bounds or not.

Once the engine is running and the compressor is ON, there are a ton of variables that come into play that will altar the readings one is seeing.


Thanks for reading.

 

Thank you.


There have been bits of crumbly foam spitting out my vents for the last fifteen years or so.

I saw a thread somewhere where someone gutted the dash on a 1980-1986 and completely replaced all those foam seals; it was a pretty intensive operation and not for the easily intimidated.

 

I read that some year-models of Fords are plagued with "Black Death" of the condensors.

My understanding is some substance within the system cakes onto the inside of the condensor walls and cooks/bakes into a hardened crust that defies all methods of flushing.

Is my 1985 included in this "Black Death" period ??


Thanks for reading.

 

Never heard of this "black death" syndrome before, but the Internet is filled with stories of just about anything conceivable... the earth is flat and the moon is made of blue cheese, for example... you can read anything you want if you keep searching for it....

 

https://ericthecarguy.com/kunena/10-...5-a-c-flushing

Here is just one of several articles I have found to mention the scenario.

Scroll down to the paragraph that starts "Black Death"

Thank you for reading.

 

From my understanding, "black death" comes from the compressor having problems, and it distributes metal dust and other particles throughout the system. So if you have a compressor failure, that's the time to look the system over and possibly flushing it clean before trying to get it going again. If you don't clean it, the black stuff gets in the compressor and ruins it, and also clogs the orifice.

Going by the measurement method is the best way I know to get the correct amount of freon in the system. Ambient conditions affect the pressures too much, and require fudge factors to go by them.

I just did a 96 powerstroke, and on the radiator sticker it specified not more than 32oz of freon be put in the system, and no more than 9 oz of PAG oil. I put in two 12oz cans of r134a, and about 8oz of oil in it, and it cools pretty good. It came from the factory with r134a. It had a locked compressor, but the orifice didn't have much in it, and the rest of the system looked pretty clean, so I rolled the dice and it worked out.

 

"Black Death" is more prevalent in later model (91?+?) Fords with the FS-10 series compressors. The original compressors for the longest time had Teflon seals that would come apart after time. They were black Teflon, and that is where Black Death originally came from. The FS6 compresses will still come apart in you, but it will be more silver/grey when you pull out the tube. It also usually won't be as bad as a Black Death system. If you want to really see something come apart, look at a newer scroll compressor after its failed. The worst offender is the 2nd gen CRV. A compressor fails on one of those and you are replacing everything. Evap, hose, cond... Everything. Of course the same goes for anything later with a parallel flow condenser. They cannot be flushed. We would not even give a warranty on the parts if it were not completely and properly repaired with visual inpection and documentation. They were that bad.

 

It has often been my experience that older is usually way better.

That being said, I have at least a dozen YORKs laying around amongst the spider-webs; two being brand-new, still with the ports capped (a swap-meet find from a vendor who had no idea what he had).

So far as performance is concerned, how well would a new YORK compare to other compressors ??

Thanks for reading.

 

The old York/Tecumseh was a work horse. They still use variants of it today in HD applications. That and the old GM A6 were pretty much indestructible as long as you fed them oil. They even used them on fishing boats for the refrigeration systems.

 

Your gauge pressures look good, on the low end of what I'd expect but your static pressure looks a little low. I'd expect something closer to 100psig given the temp.

 

Thank you for posting the pressure chart.

That will probably get printed, laminated, and attached to my gauge set.

Thanks.