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high vent temp

arnea on Sat June 05, 2010 4:59 PM User is offline

Year: 1997
Make: chev
Model: suburban
Engine Size: 5.7
Refrigerant Type: 134a
Ambient Temp: 88
Pressure Low: 130
Pressure High: 300
Country of Origin: United States

I finally was able to get a complete set of readings of my 97 Chevy suburban with dual system
88 ambient 60 constant vent temp 1500 rpm pressures 130 low 300 high. I have been playing with this for the last 2 years. Started with a full charge at 64 ounces, deep vacuum, holds a vacuum. It does have an aftermarket condenser. never seems to get a low enough vent temp...air is cool at 60 degrees but never cold... What to do??? Thanks Arne

GM Tech on Sat June 05, 2010 8:54 PM User is offline

Those pressures are like as if there is massive amounts of air in the system- or you have 2 orifice tubes in it.

If this is a rear system truck- (which by charge spec it appears to be) make sure there is no orifice that came with the new condenser (a lot of them have them in there)- If front system only- then the OT goes in condenser outlet-- if rear system- the OT goes just beyond the "Y" split in the liquid line....

I've seen 3 or 4 in my life with NO OT as well anywhere- and 2 or 3 with OTs in both places....

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......

ice-n-tropics on Sat June 05, 2010 9:18 PM User is offline

Ps = 130 psig indicates no OT or bypass around OT o-ring.
If abnormally high (4 + times normal), low pressure side was due to air in system then high side would probably be higher.
Also due to non effective expansion device, High pressure relief valve may be releasing refrigerant to the atmosphere.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Sat June 05, 2010 at 9:28 PM by ice-n-tropics

arnea on Sun June 06, 2010 7:38 AM User is offline

I had to replace the compressor due to failure and the OT had debris in it. I flushed the system and replaced accumulator, OT and compressor. what your saying is that the OT could be clogged again???

arnea on Sun June 06, 2010 7:49 AM User is offline

could the system have too much oil in it to get these pressures???

ice-n-tropics on Mon June 07, 2010 12:18 PM User is offline

Guess your pretty frustrated after all the A/C R&R. Are there A/C system modifications that we don't know about? What is the louver air temp out of the rear auxiliary evaporator?
No indication of debris in OT or excessive oil. A/C with double to triple oil have 3 to 7 degree higher louver temps and will be almost normal pressures except very slightly higher on the high side because oil insulates and decreases condenser heat dissipation. Max A/C system control mode will be 10 degrees colder than "Normal" mode on a humid or hot day.
Potential causes of Ps = 130 psig at 1500 erpm :
1) 10% probability - Compressor valves partially puked - If this is the cause then high side will probably be abnormally low also, unless system has excessive air inside A/C .
Caution : Always include suction plumbing when flushing because puked compressor debris can flow backwards upstream when A/C system equalizes high side pressure to the low side immediately after clutch disengagement. When a new replacement compressor is first engaged, suction debris will crap-out the brand new compressor's valves.
2) 50% probability - Not enough pressure drop across OT. OT could be missing. Or, high pressure refrigerant could be bypassing the OT between the OT o-ring and the external tubing where the OT is mounted. If you feel the tubing where the OT should be located the tube should be really cold (30 to 45 degrees) after the OT.
3) 20% probability - OT may be improperly located in the cond. outlet for a dual evaporator system instead of downstream of the liquid line "Y" fitting and may also have secondary defects of air or charge amount.
4) 10% probability - Item 2) with the added defects of loss of refrigerant and oil out of the high side pressure relief valve and/or air in system. You can see witness evidence of oil spray.
5) 10% probability - Misc. - lots of air in the A/C and low refrigerant amount or wierd type of refrigerant or residual cleaning fluid.

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Edited: Mon June 07, 2010 at 12:21 PM by ice-n-tropics

arnea on Mon June 07, 2010 1:24 PM User is offline

thanks for all the great information. Yes, I am very frustrated with this. It is the only dual system vehicle I have and maybe I am missing something here. The temp 60 was the same for both front and rear vents. I had a catastrophic compressor failure about 2 years ago. I flushed the entire system although I was unable to open the line in the rear under the truck. I also replaced the accumulator, OT, and an aftermarket condenser. The evaporator has been replaced also since I broke the fitting off. I was able to open the expansion valve and replace it. The OT is definitely in the Y connector area. Could I have put it in backwards???? I don't think I did...Arne

HECAT on Mon June 07, 2010 2:12 PM User is offline

Looking back you have been at it for maybe more than 2 years. This looks like the 4th summer of posts about this 97 burb. I see you did replace the rear TXV, but an older post indicated you had first tried to flush through the rear TXV with flush purchased from site sponsor. Did you reflush at the time of TXV replacement, and are you sure that it was clean and DRY before putting it all back together again. If you cannot honestly answer us (or more importantly yourself) that this system was clean and DRY before you began to reassemble and recharge, we will be discussing this for many more summers. JMHO


HECAT: You support the Forum when you consider for your a/c parts.


arnea on Mon June 07, 2010 2:27 PM User is offline

I can't honestly be sure. I do remember that I could only remove the expansion valve and i couldn't get any of lines at the rear open. What to do???Thanks arne

HECAT on Mon June 07, 2010 2:38 PM User is offline

Originally posted by: arnea
What to do???

Take it to DRY bare metal and start again.


HECAT: You support the Forum when you consider for your a/c parts.


iceman2555 on Mon June 07, 2010 7:15 PM User is offlineView users profile

There seems to be a serious problem here...possibly not only with the system...but with 130 psi suction in the heck can one have vent temps of 60degrees.....something is missing here...or the gauges are totally screwed. An outlet temp of 60 would normally equate to a evap temp of ....55 degrees.....and this temp would no way equate to a suction pressure of 130 psi.

I like HECATS suggestion...get it back to bare metal and start all over.....all over....everything back to square one....get a base line and work from there.

After 2 years....think it would be time to locate a suitable repair facility and simply get the system repaired....properly.

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

chris142 on Mon June 07, 2010 9:42 PM User is offline

The Suburban with rear AC has a tube under the battery/air intake tube. The truck and Suburban with front AC only has the tube behind the RF blinker.

Most aftermarket condensors come with a tube installed and you need to remove it if you have rear AC.

130 on the low side does sound like there is no tube installed.

arnea on Tue June 08, 2010 6:41 AM User is offline

I don't disagree in cleaning it out again. How can I make sure that the rear system is clean if the only piece I can open up is the TXV. Is that sufficient to flush from there?????? Arne

HECAT on Tue June 08, 2010 6:58 AM User is offline

You will need powerful and effective flush equipment, the right solvent, access where necessary, and confirmation. The only other option is to remove and replace the components with new. Sometimes a gutted (clearance drilled) TXV can be installed for flushing purposes. Look for alternative line connections other than the ones you cannot break (maybe even consider cut and splice). Not being able to access in the most convenient place must be overcome.


HECAT: You support the Forum when you consider for your a/c parts.


arnea on Mon June 14, 2010 8:36 AM User is offline

I am just waiting for some parts ordered from AC kits. I am still somewhat confused as to what size OT tube my 97 Suburban dual system needs. I ordered both a .072 white tube and a yellow white .062 tube. Which is the correct one???? and if I have the wrong one what impact would that have on vent temps??? thanks Arne

70monte on Mon June 14, 2010 9:42 PM User is offline

As a couple other people mentioned, did you check to see if the replacement condensor that you installed had an OT already installed in the outlet pipe?

I've replaced the condensor's on both of my 98 chevy trucks with aftermarket ones from this site and they both had OT's already installed in the outlet pipes.

Both of my condensor's came with the black/white OT's of course this was for a truck application so the Suburban probably uses a different one.


arnea on Tue June 15, 2010 2:05 PM User is offline

I did indeed find an OT in the aftermarket condensor and I removed it since I have a dual system. Arne

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