Automotive Air Conditioning Information Forum (Archives)

msgale on Wed July 03, 2013 9:43 PM

Year: 1997
Make: gmc
Model: safari
Engine Size: 4.3L
Refrigerant Type: 134a
Ambient Temp: 80
Pressure Low: 95
Pressure High: 105
Country of Origin: United States

I replaced, due to leaks, compressor, condenser, front evap, and orifice tube, dryer.
So I started charging with gas thru the low side, RPM about 500, saw the above readings. At that time
the compressor output tube was too hot to touch, ( so we know the compressor is actually compressing)
condenser output line was approx ambient temp,
Just after the orifice tube, there is frost on the line entering the front evaporator.
evaporator exit tube is ambient temp

The I closed valves, turned engine off, I heard the sound of some gas equalizing, but then the gauge readings stayed steady at:
low=95
High=40.
how could that be? is the new orifice tube clogged? with what?

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Mel G

Jag987 on Wed July 03, 2013 10:57 PM

The stupid question first, did you add oil?
Was the engine running and a/c turned on when you started filling it?
What is the system capacity of 134 and how much was added?
I am new here as well, but would like to know these questions before I offer my opinions on it, but based on what you said, they are not good.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

TRB on Thu July 04, 2013 12:36 AM

Did you put the OT in correctly?

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Contact: ACKits.com

msgale on Thu July 04, 2013 6:59 AM

added oil, distributed it among the various components,
engine on 500 rpm. , ac on,
I dont have a precise enough scale to weigh amount of 134 added. why do you ask? do you susupect it's overfilled?

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Mel G

msgale on Thu July 04, 2013 7:03 AM

well, i wonder too if there is a defect at the orifice tube. I don't know how else the system low pressure could remain higher than the high side after engine off.
I don't think it's backwards, only way to check is empty system and look at it.
would a backwards orifice tube cause these readings?

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Mel G

GM Tech on Thu July 04, 2013 8:24 AM

Your high side gage is not calibrated- should read same as low with engine off-

You only chargerd one can? Don't worry about readings until you get 75% of refrigerant in the system- with that little of charge in there- readings can be funny. Was the low side 95 reading with a can hooked up- if so you just read the pressure of the can.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

msgale on Thu July 04, 2013 8:34 AM

Quote
Originally posted by: GM Tech
Your high side gage is not calibrated- should read same as low with engine off-
that what i wondered too, How to calibrate it?



You only charged one can? Don't worry about readings until you get 75% of refrigerant in the system- with that little of charge in there- readings can be funny. Was the low side 95 reading with a can hooked up- if so you just read the pressure of the can.
i charged off a 30#, not sure how much is in.
the low side reading was with freon disconnected, so i was reading the system, not the canister



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Mel G

msgale on Thu July 04, 2013 10:01 AM

calibration: double checked , both guages are only a pound or two off

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Mel G

iceman2555 on Thu July 04, 2013 10:28 AM

First inclination would be a restricted condenser. This would be due to the excessive temperature of the discharge line. The post indicates that a certain amount of lubricant was added to each component. It is possible, even though the condenser is new, that this addition of lubricant into the inlet side of the new condenser could become a restriction...combine this with an amount of lubricant discharged from the compressor at start up could contribute to a reduction of flow. An undercharged system, such as yours, would not produce a substantial temp drop across the condenser. The drop should be about equal until the system approaches a more complete charged.

Typically when charging with a machine this addition of lubricant tot his part would be displaced as the charge was introduced into the system. Since we are adding gas to the system, it may take a bit longer to actually move this lubricant from the inlet side of the condenser. One could simply continue to add refrigerant and hope for the best, have the system serviced in the correct manner, or start over, flush the system, add lubricant to the compressor and accumulator (best method only) and then have the system professionally recharged. The serious down side of continuing in the same procedure is possible compressor damage due to excessive discharge pressures and lack of lubricant flow back the compressor due to lack of refrigerant flow. Please keep in mind, that now where in the compressor job description of the compressor does it list that the unit is designed to 'suck refrigerant into the system'. This is ole time technician 'short cut' that can result in premature compressor damage or noise issues.
Is the compressor a bit noisy also? Just curious, this could be an indication of the condenser restriction also.

The frost ring after the orifice tube is simply that the amount of refrigerant flowing thru the system is low and the resultant pressure/temperature drop is sufficient to produce this frost ring. Ford's are notorious for this, esp the blue tubes, when hand charging. This normally returns to normal once the system is charged.

The question posed by the pressure differential is a bit disconcerting also. The pressures should equalize quickly when the system is shut down. A restriction in the system could produce this slow equalization, however, would have thought the new orifice tube would account for sufficient flow to circumvent a possible restriction in the condenser. Pull the orifice tube and inspect for possible debris contamination. Are you utilizing an OE type tube or a variable unit? Does this system have rear air and if so was this section removed and flushed? Was the front evap flushed and cleaned?

What ever the outcome, strongly suggest to have the system serviced by someone with the correct equipment....from the post..it appears that pressures are your guiding factor to determine the proper charge rate....this will result in a undercharged system and premature unit failures.

Good luck.

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