auto a/c

1992 chevy ex cab.comp seized remove replace compressor and dryer .original r-12 unit Vac down put in 134 2 lbs .High side 200 lbs low side 30 it wont cool below 60 to 70 coming out of the ducts . Tried put in more freon up to 250 on the high side no better .then removed freon so it was 175 on the high side still dont cool.any ideas?

The condensor may be inefficient 'cause it's clogged with remnants of the old compressor that even flushing won't remove.

Also, did you check the oriface tube?

What Bob said.

Your gauge readings are telling you that the system is plugged up; high side is too high and low side is too low. A good, clean system will read 42/165-170(your high side will vary depending on locale, ambient temp and humidity).

Did you disassemble the system’s high side, flush it out entirely and replace the orifice tube?

They "always" plug the orifice tube and "many times" will plug the lower end of that condenser when a compressor unravels.

Go in behind the right front park light. Ya have to take out the light assembly. Behind it, there is a pipe connection; open it up and that orifice tube lives inside the condenser-side pipe.

Pull the plastic end of the little tube out with a pair of needle-nosed pliers and you’ll see what I mean. Screen is gonna be chocked full of lost metal and black mud.

Flush 'er all out with a flushing agent and REPLACE that little orifice tube.

Then, after you get it back up and running again, look at the condenser while in operation. If you see any evidence of frost along the lower 3-4” of it’s width, the condenser is plugged and will probably need replacing. If it is hot across it's entire width, its okay.

Allan

If you have a lot of miles, replace the fan clutch. The fan must be able to pull air through the condenser. The rule of thumb for 12 to 134 conversion is 80% of 12 capacity. Not all systems will be this rate, but its a very good place to start. To get at the orifice, its much easier to take the whole grille out. How deep did the vacuum get? If your orifice were plugged, both high and low pressures would be low.

Why would pulling the grille out make changing the orifice tube easier?

I put a new orifice tube, compressor, dryer and condensor in my 91 Suburban - and the orifice tube was in the line going to the evaporator on the firewall - nowhere near the front grille.

But - maybe his 92 truck is the new body style? I kind of lost track since GM mixed up the body styles late 80s and early 90s. My 91 Suburban is "old body style", and I know 1/2 trucks had "new body style" starting around 88. And - I have no idea if it makes any difference in the AC system.

When I fixed mine last summer- and retrofitted to 134A - it read 40 PSI on the low side and 250 PSI on the high side - on an 80 degree F day (humidity unknown). It worked fine then and still does - blows 48 F air at 80 F degrees air temps. On some real hot days I've seen the high side go to 300 PSI.

I do know the pressure readings in themselves can be misleading unless put into proper context - and often a thermocouple temp reading of discharge line is needed along with them.

Every GM I ever had - with a trashed compressor - had chronic orifice tube and screen plugging problems until I replaced the condensor - since it's near impossible to ever get it flushed out properly.

Seems some shops now put a filter on condensors - to stop the debris from travelling through the system.

Like others said , oriffice tube , make sure condensor is clean . I show r134 charge to be 44 oz .

Yes Sir,

The '91 Sub and tonners were still the old body style.

Allan

I'll give ya another rule of thumb from the field and "outside the book" for any system/any freon.

Fill it until it is to the point of being so cold that you cannot comfortably hold your hand on the receiver. At that point, the system is at optimum charge.

Allan

Is the suction line cold? Is the accumulator cold? The readings sound pretty good to me. If the orifice tube were plugged the low side would be in a vacuum and the high side would also be low, unless you have an overcharge which will distort readings. Put a C clamp on the output heater hose to be sure something is not wrong with the air blend door and see if it cools.

I just went through that - sort of - on a 98 Dodge Grand Caravan with front AC only with optional HVAC computerized controls.

Put a new compressor and dryer in it. The previous compressor had a slow shaft-seal leak - i.e. it wasn't trashed.

Got all done - pulled a vacuum for two hours and then charged exactly to specs - 34 ounces of 134A. Then ran it - it would blow cool air at first (cool - not cold), and then get warm after five minutes. I checked low side pressure and high side pressure against outside temps. Also checked high-line temp. All checked in-range as to the factory book. Dodge provides one of the most comprehensive charts I've seen with all pressures at all line temps, evaporator temps, and air temps.

Everything checked pefect but the thing would not cool. In perhaps a stupid bout of desparation - I added an extra 12 ounce can - and the duct air temp went down from 68F to 58 degrees F (on an 80 F degree day). I then added a second 12 ounce can and the duct temp went down to 50 F degrees. So - I got all done and it now works pretty well. It passed the computerized cool-down test. Low and High pressures with the two-can overcharge still pretty much read the same as before - with the low side slightly higher.

I've got no answer to this one - except it now works and I'm going to leave well enough alone.

I had been suspecting that maybe some of my 12 ounce cans - some 10 years old - were maybe not completely full? Well, now I doubt it. I checked one - 15 ounces full and 3 ounces empty - right on the nose.

It was running 38 PSI on the low, and 270 PSI on the high at 85 degrees F. Dodge factory manual says that at 80F - normal is : low at 17-35 PSI and high at 230 - 360 PSI. Air coming out of the AC duct should be 38F to 50F.

This one's a bit beyond me - but it's working good enough for now - especially since I'm sick of working on it.

Ya darned right.

After a time playin' with the wrenches, ya get to the point where ya just plain fly by the seat of yer pants.

I threw those darned books away a hunert years ago. :>)

Allan

Condenser core is clogged/internally corroded. I can almost guarantee the cores will be full of white powere (oxidized aluminum)

Hello 620 row crop.
For a system to be fully charged the low side line going into the compressor has to be sweatting
If you keep adding refrigerant the line will start to freeze, you then take out the excess untill the frost disappears.
Goo Luck!
For a 134a system 30 PSI. on the low side
200Lb on the high side(I assume that it is at idle) sounds a bit low. Evaporator line should be about 39* and I think R134a at that temperature has more pressure then 30 Lb.
Guido.

The orifice tube is in the outlet of the condenser. I don't know how you'd be able to get the lines apart by reaching sideways through the parking light.
According to GM service info, the orifice tube moved from the inlet on the evaporator to the outlet of the condenser on C-K trucks with the exception of vehicles with optional rear a/c for 86 model year. They have a crimp in the condenser outlet to prevent an orifice from being installed. They use a Y tube with the orifice mounted after the split for the front and a thermal expansion valve for the rear unit. For a 92 model year with front a/c only, 39oz of R-12.