Don't know this one.......?????

reno · Mar 25, 2008

Got my manifold gauges today and tried them out. OK, maybe Makg will know this one, then again someone else here might beat him to it.

When I hooked up the gauges <engine off> they read 95 PSI LOW side, and ( I really don't remember the exact reading) about 110 PSI HIGH side.

Then <engine on> they read (and this is where I get lost in this maze), 180 - 200 PSI HIGH and Max movement of the needle high end of LOW side while clutch is engaged, when Clutch disengages, LOW side needle drops quickly and HIGH side remains about 180 - 200 PSI. I am thinking moisture in the system, which means P.O. did not replace the drier, possibly pump the system correctly either.

What do you guys think, I am still learning all this A/C stuff and don't really have a clue. :dunno:

reno · Mar 26, 2008

OK, I have been thinking about this, and it actually might be a blocked orifice tube. But with me not knowing the original history of this truck or the repair of the A/C (was a R-12 system) could still have moisture in the system or worse yet, never pumped down.

thegoat4 · Mar 26, 2008

You're not very clear. What were both the highest and lowest readings on the low side? What were both the highest and lowest readings on the high side? Are the pressures steady or do they flutter?

And make sure you check after the system has run for a little bit and stabilized. Even screwed up systems will settle on a pattern.

The low side should DROP when the compressor comes on. If the low side rises, you either have the lines reversed, or you have a blockage somewhere between the low side port and the compressor suction.

Also, what are the problems with the AC to begin with? No cooling at all? Weak? Blowing hot like the heat is on?

reno · Mar 26, 2008

the A/C blows cool, but not cold like it should, at around 62 - 64 Degrees when it is 80 degrees ambient. I do not know anything about this system, who repaired it, replaced parts are new,rebuilt or junkyard and so on. I bought some R134a gauges and wanted to check the system before I blew it apart this summer. Looks as if though I will be replacing an orifice tube, drier and possibly a compressor.

I checked the system with the engine off to see if both sides were at 125 PSI, the readings were 95 on the low side and I think 110 or 120 high side. Engine running System on max cool fan on high, readings were needle pegged to the right, that is what 350? When I get home today, I will run the system for about 5 minutes and take the reading.

thegoat4 · Mar 26, 2008

Readings on what? Pegged out at 350 on the low side is really really really bad. pegged out on the high side is less bad, but will still beat the hell out of the compressor and fry the oil. Might even blow a line off.

Why do you think you already need a compressor? If it can peg your gauges, sounds like it's working for now.

For the readings with the system off (static pressure) to have any meaning, let the system sit a while, (as in until the engine cools off) then check. Also take note of the ambient temperature. If you check with a hot engine compartment checking static pressures doesn't do much aside from verifying that the system is not empty.

Also, earlier you said the system was an R12 system, now you say you hooked up R134a gauges. Which is it? That makes a big difference.

Often the high pressures can be caused by a dirty or blocked condenser core. But you should have a high side switch to turn off the compressor before it gets too high. Has the wiring been "modded"? It's not uncommon for people to bypass failed switches.

reno · Mar 26, 2008

Clutch cycles,no apparent mods to the wiring and if you read closer I said it WAS an R-12 system, it has been been converted, but not by the cheesy wal-mart conversion. Hoses have been changed with the R-134a fittings, just like factory.

The engine was cool when I first connected the lines. Then I started the engine, turned the A/C on max and fan on high. Waited about 2 - 3 minutes and took the reading. I will hook them up again, and run the A/C for around 5 minutes or better, take the reading, and post the results.

reno · Mar 26, 2008

reno said:
OK, I have been thinking about this, and it actually might be a blocked orifice tube. But with me not knowing the original history of this truck or the repair of the A/C (was a R-12 system) could still have moisture in the system or worse yet, never pumped down.

Right there in red......

reno · Mar 26, 2008

OK, So I have been home for around 3.5 hrs now truck is cool. Hook up gauges.
Engine Off
LOW= 100 PSI and HIGH= 100 PSI

Engine Running Max A/C
Low= 26Psi Clutch Cuts out then @ 50 PSI Clutch Cuts in

High= 175 PSI Cuts out then @ 95 PSI Cuts in

Clutch cycles for about 20 - 25 seconds (on for 20 - 25 sec), Off for about the same amount of time

After Running A/C and engine off for 3 minutes

Low= 65 PSI High= 65 PSI

That is where I left off.

Now it sounds low on R134A.....Hmmm

skippy · Mar 26, 2008

sounds like a leak.when a/c off,and pressure around 100 psig,paint all connections w/mixture of dish soap and water mixed.if a leak is present,the solution will blow you a bubble.

pressures need time to equalize between high side and low side,usually about 3-5 minutes or you could see really high side pressures and low pressure on low side.

if the system was not evacuated,or ecacuted with unknown leak then moisture is a real possibility.moisture flowing with refrigerant and oil will freeze up @ the orifice and eventully close over,giving low reading on low side,high reading high side.compressors hate this and will eventually say good-bye.

hope this helps,read mikes sticky and get yourself a p/t chart for 134 and other refrigerants.happy wrenching,skip dawg.

reno · Mar 26, 2008

well if a leak is suspected, I will use UV leak detector. that is the best bet I believe. But there is the possibility that the system was not even filled properly.

VaGent · Mar 27, 2008

With the compressor cycling on & off so quickly, that's a good indication that the system is LOW on refrigerant. Slowly add a couple of ounces & see if the compressor runs longer each time you add it. It sounds to me like it's never been charged correctly to begin with. Keep in mind the outside ambient air temps when you are charging the system. Keep all the windows & doors closed to the truck too. Do you have a calibrated thermometer to measure the discharge air with?

skippy · Mar 27, 2008

check for leaks before topping off system,don't waste refrigerant and money.

reno · Mar 27, 2008

I was going to buy the UV refrigerant, they are mixed together. Simply put that in, and wait to see the green glow, then presto, there is the leak.

Now on manifold gauges, I want to make sure I read this correctly in the book I bought, When I add refrigerant, hook up to the yellow line, keep the red (High Side) valve turned off (at the gauge) and only open the Blue line (Low side), when done,turn off the Low Side and check the readings? I don't need the High side coming into the fill (Yellow) line, would not be a pretty site. :icon_thumby:

skippy · Mar 27, 2008

reno said:
I was going to buy the UV refrigerant, they are mixed together. Simply put that in, and wait to see the green glow, then presto, there is the leak.

Now on manifold gauges, I want to make sure I read this correctly in the book I bought, When I add refrigerant, hook up to the yellow line, keep the red (High Side) valve turned off (at the gauge) and only open the Blue line (Low side), when done,turn off the Low Side and check the readings? I don't need the High side coming into the fill (Yellow) line, would not be a pretty site.

you seem to have a handle on the gauges.i might add purge the gauges upon hook up so as not to introduce air into the system.to do this hook up the gauges,when pressure is showing,loosen hose at manifold just enough to bleed refrigerant for 1 second to blow air out of the hose.same for the refrigerant hooked up to the charging hose.

as for uv leak detection,it is your money.soap bubbles are cheap,readily available and they work in the presence of pressure.i do it every day on commercial and some residential systems.if a unit is completely out,we pump it up with nitrogen.about 100 psi most cases will show a leak.

reno · Mar 27, 2008

Well I can try the soap trick, what do you figure, about 4 drops of detergent to 16 oz spray bottle? I know on vacuum leaks on the engine I use about 2 drops of dish detergent to 16 oz spray bottle of water.

Don't know this one.......?????

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