Year: 1999
Make: chevy
Model: Tahoe
Engine Size: 5.7l
Refrigerant Type: R134a
Ambient Temp: 88
Pressure Low: 45
Pressure High: 350
Country of Origin: United States
My son recently purchased this Tahoe. A/c wasn't cooling well hooked up gauges and got the above readings. We then cleaned the condenser & rad.,changed fan clutch,evac system,vac down for 1hr. w/5cfm pump.Recharge w/12oz cans of R134a only. At 3 cans pressures started reading hi. At 4 1/2 cans [52 oz] pressure readings were back to the same as before. Vent temp 70-72 deg. Line sweating in & out of evap. Vacuum heater valve is working.I'am stumped. Please help. Thanks in advance
Did you replace or check the orifice tube? It should be in the line connection right before the "y" that goes to the rear air that is located on the passenger side of the engine compartment.
Wayne
Thanks for the reply. Is there anything i could check before i evac again? Would o tube cause hi pressure readings? What o tube should this dual air system have?
Update: Pulled o tube and it was clean (just oily) no debris. I did notice when i pulled the lines apart the o tube was part of the way in the rear line.Got it out cleaned oil off it then pressed it into the front line where it should be. Vac system down then started to recharge. With 3 1/2 cans in both pressures again were HI. Line from o tube to firewall sweating.Receiver dryer very warm. My son took bottom cover off heater box he could see a door open & close when he switched control from cold to hot. Are there any other doors in the heater box for the a/c? ANYONE HAVE ANY THOUGHTS WHAT MIGHT BE GOING ON HERE?
What are the pressures at 1750 RPM? Are you using the correct OT? There are 2 types evap mounted and condenser mounted.
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Thanks for the reply. Pressures above are at 1500 rpm. The o tube is condense mounted white in color. Is this the correct setup? If the o tube moved out of place ( to the rear) would that cause both pressures to be hi?
Also is 64oz the correct amount for this dual system? Thanks trb for your help.
Condenser mounted OT is for front air only trucks. A dual air setup would have one evaporator mounted tube, after the Y in the liquid line, so that only the front evaporator is fed through an OT. The rear TXV must have unobstructed flow from the condenser with no OTs in that path.
Since this system has apparently been worked on before, by someone who didn't know what they were doing as they messed up the OT placement, you should also consider the possibility of having way too much oil as the cause of the excessive pressure.
Edited: Sun July 24, 2011 at 9:47 AM by mk378
Sorry my mistake it is mounted just as you said it should be. The y is nearest to condense my bad. Is white the correct color, 64oz? If o tube moved out of place again would that be causing the hi pressures? Thanks mk for your help
Update put in new white o tube and back system for 1 hr. Recharge system rear a/c is working 57 deg. Vent temp. But front a/c blowing 95 deg witch is outside temp today. Pressures at 1500 rpm 35&300. Small lin
Sorry posting on cell phone
Small line going into evaporate sweating but receiver dryer is very warm. My plan is to remove dryer & blow air into evaporater then put on new rec. Would 2 oz of pag 150 be correct? Does this sound like the correct plan? Thanks for all help.
Replaced accumulator added 2oz pag 150 blew air through evaporater. vac & recharged. Pressures at 1500 rpm low side 48 hi side 360 outside temp. 95
Front vents 74 deg rear vent 58 deg. What should i do next? I'am stumped.
The correct orifice tube for this system is YELLOW. It should have a 'star' shaped end to prevent 'blow back' into the liquid line. If this 'star' is not there...as in the standard 'white' tube...the orifice can be pushed back in the line by pressure and thus no cooling of the front unit. The rear will work because it is getting the correct refrigerant flow and has it's own TXV.
The excessive head pressures (discharge) tend to point toward a restricted condenser. Is not the high side port located on the suction/discharge manifold on top of the compressor? The fact that the orifice tube is not 'trashed' does not mean that the condenser is not restricted.
Also, one other aspect of the condenser mounted on this vehicle. It can be mounted upside down or the discharge line/liquid line can be reversed. Make sure that the discharge line from the compressor is attached to the top connection of the condenser. Also check the condenser for the location of the orifice tube. GM uses the same condenser for both vehicles. The location for the orifice tube is different but the flow of the condenser is such that if it is mount incorrectly...the result is an increase in discharge pressures.... The liquid section of the condenser will have several small 'dimples' in the metal line. This is the sealing location for the condenser mounted orifice. This line should be on the bottom of the condenser and the attached line should lead back to the 'in-line' mounted orifice.
Good luck...any more questions....let us know.
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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson
Thanks iceman. I will change o tube to a yellow one. Yes both ports are on top of the compressor.I will also check the condenser lines. Will post back with results.
Just checked with parts store and the o tube that i put in is the yellow one ( but the head is white ). How far does o tube go into the line? O-ring before dimples in the line or after the dimples?
Lubricate the oring with mineral lube and slide into the inlet. You should be able to 'feel' the resistance when the orifice 'seats'.
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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson
If we change the condenser how much pag 150 do we add?
Prior to changing the condenser...did you complete the connections as stated in a previous post? Determine if the condenser is truly at fault prior to changing the unit. A simple test would be to start the vehicle...operate at max cool/high blower/doors open/engine at idle for about 10 minutes. Touch (do not grab) the discharge line (between the compressor and condenser). If this line is extremely hot....the condenser is probably restricted.
However, this same condition could occur if the line connects are reversed....check the hose routings first. This is very important.
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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson
Will do the above tests. But I need to know how much oil to add if we change out condenser.
Ok discharge line from compressor does go to top line of condenser. Ran truck for the 10 min test discharge line at compressor & condenser were very hot (if touch for 2 sec or more would blister you).
HOW MUCH OIL DO WE ADD TO NEW CONDENSER?
ANY OTHER POSSIBLITYS I SHOULD CHECK?
Thanks for all the help.
Do not add oil to the new condenser! It is doubtful that any lube will drain from your unit. If you desire to add a bit of lube...add 1-2 oz to the accumulator.
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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson
Thanks iceman will post back with results once we are able to make repair.
Why do you have this obsession with adding oil at every turn when you don't know how much there already is, and symptoms suggest there may be too much?
Installed new condenser vac system for 1 hr. Pressures at 1500 rpm 86 deg.
Low side 48psi hi side 320
front vent 70 deg.
rear vent 58 deg.
4 lbs of r134a
NO OIL ADDED TO CONDENSER CHANGE..
What should we do next??????????????
Anyone have any ideas what could be causing front air not cool correctly?
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