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pressures for 2004 Trailblazer EXT

Sprig Rig on Wed July 29, 2009 10:14 PM User is offline

Year: 2004
Make: Chevy
Model: Trailblazer EXT
Engine Size: 4.2
Refrigerant Type: r134a
Ambient Temp: 96
Pressure Low: 45
Pressure High: 5
Country of Origin: United States

My wife's Trailblazer a/c cools okay, but blows warm air when you stop the car or put into park. I checked the pressures with a set of gauges the low side (blue) was 45; and the high side (red) was only 5! The air temp is about 96 F and humidity is about 50 %. I plan to borrow a vacuum pump and vacuum the system completely and see if it will hold a vacuum for the 30 minutes; then recharge the system. Should I be looking for anything else? Can someone please provide me with the proper low/high pressures.

knightgang on Wed July 29, 2009 10:34 PM User is offline

The Pro's on here will tell you that pressures are just to check performance. If you are going to vacuum and recharge, be sure to add dye back into the system to that it will mark any leaks that you might have. I suspect a leak in your system somewhere, elsewise your high side presure will not be so low unless you have a blockage somewhere before the high side service port.

See what the likes of GMT, Chick and the others have to say...

Chick on Thu July 30, 2009 6:52 AM User is offlineView users profile

you cannot get any cooling with a high side of 5psi, just won't happen, so you have the gages hooked up wrong, the high side is not depressing the shrader valve, and until you fix the problem with your gages, I would not recover the refrigerant just yet, there may be nothing wrong with your system other than poor air flow, compressor shutting off when the temp rises etc.. start again and make sure you get the proper high side readings and post back.. when it begins to blow warm, check to see if the compressor is engaged...

Email: Chick


Freedoms just another word for nothing left to lose

GM Tech on Thu July 30, 2009 7:46 AM User is offline

Fix your high side depresser connection- 5 psi is impossible--the study that electric actuated clutch fan

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......

NickD on Thu July 30, 2009 9:11 AM User is offline

We need one word to express posting pressures to determine the charge status, doors open, AC on, blower at maximum, engine running at 1,500 rpm, both manifold valves must be closed tight, ambient temperature must be at least 80*F and just as important to post whatever it is as well as the pressures, and observations should be made as to whether the compressor hub is rotating or not, it should be rotating.

It's also good to post the same pressures at idle speed, this can paint a different picture. Even more data like posting the inlet/outlet temperatures of the evaporator tubes is good information.

Seems to be a lot of blank spaces in the new topic post:

Message Title:

Engine Size:
Refrigerant Type:
Ambient Temperature:
Low Side Reading:
High Side Reading:

Perhaps a note to how to post pressures would save a lot of time.

HVargas on Thu July 30, 2009 11:36 AM User is offlineView users profile

Sounds like either an airflow issue or a minor leak of the refrigerant. Getting the pressure's will help us out and let us know what is going on. Here is some information for you about the pressures of your vehicle and capacity.

W/O Rear Air - 1.9lbs
W/ Rear Air - 2.65lbs

With an ambient anywhere between 86* and 105* here are you stated pressure ranges.

Low Pressure 36-56 depending on humidity and ambient temp. Obviously the higher ambient, the higher allowable pressure.
High Pressure 200-285 once again depending on humidity and ambient temp.

Once you get the gauge problem fixed give us some pressure numbers with the vehicle running at 1500rpm and at idle. My guess is going to be with GM Tech. That electronically actuated fan clutch is a good place to start in your situation. Although an expensive one.


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cc61 on Thu July 30, 2009 1:16 PM User is offline

I do remember there was a tsb on an over charged condition on on some of the earlier trail blazers......

Sprig Rig on Thu July 30, 2009 9:14 PM User is offline

I will check the pressures again tomorrow and repost the results. I have very little experience working with auto a/c; just checked the pressures a few times long ago on an old truck we had, and added a little freon with a cheap low side kit. I am interested in learning how to start working on the a/c systems properly myself. The gauges I used were borrowed, and actually brand new, and first time used; so I can't rule out them being bad. I will check the levels in the above listed Trailblazer, and also in my truck to see if gauges are functioning properly; but admit it was probably an error on my part from little experience. I would like to THANK everyone that has provided assistance with my problem.

I am considering buying the DIY Starter Kit. Can anyone comment on this kit that has bought and used it?

Chick on Thu July 30, 2009 10:46 PM User is offlineView users profile

Mastercool tools are all I use. The kit offered by this site is MORE than enough for the DIY'er, and please stay away from those death kits.. Also, new gages, if they were cheap ones like Harbor Frieght, you're better off throwing the money out the window, just my opinion....

Email: Chick


Freedoms just another word for nothing left to lose

Sprig Rig on Mon August 03, 2009 7:48 PM User is offline

I was able to get a proper reading on the pressures. As I thought, I didn't have the high side hose connector open; I am using a new set of ATD 3691 gauges. The low side pressure was 64-66 and the high side pressure was 225-240. I monitored the levels for about 15 minutes with the a/c on high and doors open. You can clearly hear the compressor kick on and off. The air temp was 96 F with 50 % humidity. I bought a digital thermometer and placed in the center vent; while driving the temp got as low as 45 F while moving, but if you stop the temp will quickly rise. The Trailblazer was in a wreck before, and I noticed under the frontend, passenger side, there is some kind of finned cooler, evaporator maybe?, that is bent in half, in a U shape. Please continue to provide advice. Thank ya'll!


Prospeeder on Mon August 03, 2009 7:54 PM User is offlineView users profile

Im gonna say its that poor designed electric clutch fan

1990 Pontiac Turbo Grand Prix
1990 Pontiac 6000 LE V6
Both have R12 A/C

Chick on Mon August 03, 2009 8:24 PM User is offlineView users profile

A small cooler may be a trans or oil cooler, you should have it fixed, and make sure that the condenser is clean and free of dirt. I would also evacuate the system and recharge into a deep vacuum the proper amount to see if your cooling returns.. And note the pressures when you recharge it.. Your low side is to high to provide proper cooling..

Email: Chick


Freedoms just another word for nothing left to lose

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