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high side pressure reads 0

josh77888 on Tue August 17, 2010 3:10 AM User is offline

Year: 1995
Make: GMC
Model: Jimmy
Engine Size: 4.3L
Refrigerant Type: r-134a
Ambient Temp: 85
Pressure Low: 40-45
Pressure High: 0

Charge was low so i put in a can, clutch was engaging but no cold air. So hooked up gauges and those were the readings i got. High side is defenitly a problem, im just not an expert when it comes to ac systems.
I evacuated the system and i have the proper amount of refrig. to fully charge the system( 30 oz). But i don't wanna put the new 134a in it and just waste that money when i got more problems to deal with.

So far i have replaced the orifice tube and thats about it.

Any ideas why the high side is reading flat 0.

Tennessee_Timmy on Tue August 17, 2010 6:54 AM User is offlineView users profile

double check that the hi side coupler on your gauge set is depressing the valve in your hs connector.

Good Luck 2 ya,

mk378 on Tue August 17, 2010 9:15 AM User is offline

It must be a bad connection to the gauge hose. There is no way the high side can ever actually be lower pressure than the low side.

If the system is now empty (zero psi) do this to test if you have a good connection. Connect the manifold to the car, connect your vacuum pump to the yellow hose and start it. At first, open only the high side manifold valve. You should see the low side gauge go into vacuum, proving that the pump is removing air from the car through the high side hose, and the increasing vacuum is being detected through the low side hose. So you then know both shrader valves are open. Once that checks out OK, open the low side manifold valve too and complete the evacuation. It's good to do this at every evacuation to make sure that you really are connected to the car properly and not just pulling a vacuum in your hoses.

josh77888 on Tue August 17, 2010 12:11 PM User is offline

thats the thing we check the connection about 5 times. so maybe it was just a fluke, should i just try and and refill it and hope for the best.

Another question is i can't turn the clutch by hand which is normal from looking info up on these compressors you need a "spanner wrench" whatever that is to rotate the compressor.

But the question is after i vaccumed the system a couple days later i was visually inspecting the compressor and i could now turn the compressor with my hand, but it didn't sound very good.

Is this caused by the no charge in the system? Also my old orifice tube had purplish colored oil on it is that right?

sorry for all the questions im not good at ac systems and i have a little one who gets fussy in this Michigan humidity.

thanks in advance

77shovelhead on Tue August 17, 2010 1:50 PM User is offline

Checking it is one thing. Being positive that is is right, is another.

Case in point, I got the wife's Olds back together after replacing the compressor, condenser, OT, and flushing evaporator and lines. Vacuumed the system, charged and everything looked good to me.

Sent the wife off to work the next morning and she got 2 miles from home saying that the AC is not working. I told her to bring it back and I found that the compressor would not come on.

I checked the wire plug connection to the compressor and it LOOKED to be plugged in. I took the car for a drive and the AC worked sometimes and sometimes not.

I checked everything over and over. Checked and rechecked.

I reached under the car and TOUCHED the wire connector to the compressor and it engaged. I TOUCHED it again and it went off. (see the light bulb over my head)

I pulled the connector off and it was missing the rubber grommet that seals out dirt and water. It was not making a good connection without the grommet. Loose connection.

But I CHECKED the connector several times.

Check the high side hose, connections and fittings

Quality is never an accident it is always the result of intelligent effort.

Edited: Tue August 17, 2010 at 1:51 PM by 77shovelhead

josh77888 on Tue August 17, 2010 6:58 PM User is offline

alright guys i just went out there and decided to put some 134a in it, the system was completely empy but yet the compressor kicked on with less then a quarter of the can, only used about 1/2 of the can all together.

Still blowing hot air, also i checked the high side port. Tryed to depress the valve on the high side and nothing came out. Did the same to the low side and it shoots out lol. So its not the gauge giving a bad reading. It truely is putting out 0.

Compressor bad? cuz it was running about 15 mins and i was watching the gauge and it would bump up in pressure every couple of seconds, looked at the clutch and it looked like it started to skip, so i shut the truck off. Radiator has a crack on driver's side top above the rubber hose were the metal line go in.

Could that be a problem? Also i dont have a fan shroud on it, another problem possibly? lol sorry with all the questions

bohica2xo on Tue August 17, 2010 8:42 PM User is offline

Your gauge port schrader valve is plugged up. Has anybody put sealer in the system? It is NOT at perfect atmospheric pressure on the high side.

The missing fan shroud is a big issue. You can expect some high pressures until you correct that.

Running with a partial charge will kill the compressor eventually. So will running without a shroud.

The system should be evacuated, and the high side port dealt with. The fan shroud should be installed. THEN you you can begin to diagnose the system.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

josh77888 on Wed August 18, 2010 6:26 PM User is offline

another thing is it doesn't have the proper fan on it.It is suppose to have a fan clutch type, but the guy i got it from put a standard small block fan on it so it spins all the time???

I dont know about sealer in the system, but how could it plug up the port that bad and not the low side port?

98audiA4 on Thu August 19, 2010 8:32 AM User is offline

sure you're hooking it up to the high side port and not the high pressure relief valve or some other unrelated thing? like others have said, there's almost 0% chance that you have no pressure on the "high side"

bohica2xo on Thu August 19, 2010 1:18 PM User is offline

If you depressed the high side schrader ( a dangerous way to check!) and nothing came out - it is plugged up.

Once you have recovered the refrigerant from the system, and you know the low side is at atmospheric pressure or lower you can remove the high side valve. I would not stand directly in line with it even with the low side at zero.

Since you are describing a fairly large leak, it should be easy enough to find.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

josh77888 on Thu August 19, 2010 7:13 PM User is offline

thats the thing its not leaking. Yes it is the high side that im checking its the bigger one outta the two.

So i should replace the high side port for starters?

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