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Paul M ASE Master
Paul M ASE Master, ASE Master Tech
Category: Chevy
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Experience:  ASE Master Tech 20+ Years
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2005 2500hd a/c started blowing hot air, 134 level is in the

This answer was rated:

2005 2500hd a/c started blowing hot air, 134 level is in the alert (over pressure) area of my gage.
never touched prior to today

Hello and thank you for using Just Answer


if your cooling fan clutch is bad it will cause poor cooling and high high side pressures


does it cool when you are going down the road ok?


say on the highway for example?



Customer: replied 7 years ago.

I was driving along this morning with the a/c cooling like normal, then in an instant it began to blow hot air and continued to do so the remainder of the trip. After 4 hours down time it cooled well for maybe 5 minutes and then blew hot air again for the remainder of the 25 mile trip home.

Got fan speeds, the compressor seem to be functional, the small diameter coolant line near the firewal is cold, the low pressure line is cold. ( i don't get it) It's almost like the heat regulator is all the way up in the cab but it is not.

so when this happens the low side line is cold to the touch and sweating as it should?


this has a blend door actuator for both driver and passenger side


does the passenger side get warm at the same time?


this is the automatic AC system?


if your high side pressures are going too high its probably not the inside controls causing your problem


there are known problems with the condensers being clogged with metal shavings


click here to view testing information on this


are you getting near 400 psi? if so it will not be able to cool at all.


let me know what you find and if you need more help



Customer: replied 7 years ago.

The low side line was cold and sweating when I popped the hood to check.

As far as I could tell it was blowing hot from both sides.

This is not the auto system, it has driver and passenger side slide controls.

My gage is a cheap deal for adding freon, it goes from "Low" to "Full" to "Alert" to "Danger". The "Alert" ranges from 45 to 65 PSI.


Any Idea?

there are too air temp actuators that move the doors in the heater box


if the low side line going through the firewall is frosty and it is pushing heat


you need to verify these actuators are moving when you change the temp control



click here to view page 1 of the wiring schematic


click here to view page 2


you need to check the left temp door actuator

1. Check for Left Mix Door Actual, and Air Mix Door Left Commanded on the scan tool when the temperature changes on its own.

2. Check the right I/P junction block located under the dash on the right side, connectors C4/X4 & C5/X5 for poor terminal tension, backed out terminals or connectors not fully seated.

3. Check the actuator connectors for poor terminal tension, backed out terminals or connectors not fully seated.

4. If no wiring issues are found and there is still a concern with an HVAC actuator, before replacing the actuator perform a reset of the front HVAC control head. To perform a reset remove the "HVAC BATT" fuse for one minute and reinstall. After the fuse has been reinstalled start the engine and allow it to run for one minute without using the hvac controls. After one minute use the Tech 2 to perform a door relearn procedure by entering Body/ HVAC Control Module/ Special Functions/ Recalibrate All Motors. If the actuator begins to operate, no further repairs necessary. If the actuator still does not operate perform normal diagnostics, by first checking for any new DTCs.




there is a relearn that can performed on the unit with a scan tool


click here to view the left actuator image


you can try removing the actuator and moving the door manually to see if it cools. if it does the problem is with the control unit or the actuator


let me know how you make out



Customer: replied 7 years ago.
What scan tool do you recommend?

well code readers will not work for these type of functions


you need a compatible scan tool which can be more than 1000 dollars


first see if the problem is even with the actuator or signal by removing the actuator at the bottom of the heater box and moving the door manually


just to verify it is a control problem



Customer: replied 7 years ago.

Ok, I started the truck and the ac is functioning again, the slide controlls make the air cold or hot, the knob moves the air from the panel to the floor to the upper defrost vents.

Do you believe this is an intermitant electronics problem?

I have see GM products do this type of thing before but it has always been short lived(15 min or less)

yes it could be intermitant in the blend door actuator or the control head


but I think trying the re-calibration would be a good first step



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