A/C problems 03 Z71 Tahoe

[biggsteve97]

I have an 03 Z71 Tahoe with the automatic digital climate control and at the end of last summer the front intermittently would get warm though the rear was fine. I put my gauges on and the pressures where exactly where they needed to be with no indication of a blockage. That said now its not cold front or back when i checked the compressor is not kicking on, I tried to bypass the cycling switch only to realize there is no power at the connector. I do have intermittent electrical issues where i loose all sound including warning chime through speakers and memory seats do not retain settings periodically. I question the integrity of the body control module but would the control head in the dash cause a no power issue at the switch. There are multiple lights burned out on the control head and the rear defrost does not always turn on on the first try. Ideas?
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[clinebarger]

Originally Posted by biggsteve97

I have an 03 Z71 Tahoe with the automatic digital climate control and at the end of last summer the front intermittently would get warm though the rear was fine. I put my gauges on and the pressures where exactly where they needed to be with no indication of a blockage. That said now its not cold front or back when i checked the compressor is not kicking on, I tried to bypass the cycling switch only to realize there is no power at the connector. I do have intermittent electrical issues where i loose all sound including warning chime through speakers and memory seats do not retain settings periodically. I question the integrity of the body control module but would the control head in the dash cause a no power issue at the switch. There are multiple lights burned out on the control head and the rear defrost does not always turn on on the first try. Ideas?
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Having a GM Tech 2 scan tool is the only "fast" way to diagnose your Auto HVAC system. But I will try to walk you through some basic stuff.

TESTING COMPRESSOR CLUTCH/WIRING.
Key on engine off, Jump the A/C clutch relay from pin 30 to pin 87, Compressor clutch should "click". If no click, Check for power at the green wire at the compressor. Check the black wire for ground.

TESTING LOW PRESSURE SWITCH.
With the truck running, A/C turned on. Check the Dark Blue wire at the low pressure switch for 5v with the switch Disconnected. Check for ground on the black wire. With the switch plugged in BOTH wires should show ground. If the blue wire still shows 5 volts.....Your low on freon or the low pressure switch is bad.

TESTING HIGH PRESSURE SWITCH.
1. With key on, disconnect the A/C pressure sensor and check for 5 volts on the Gray wire. Check for ground on the Black wire.

2. If missing either circuit, check a few inches back from the connector and see if voltage or ground is present there.

3. If the above checks are OK, then plug the sensor back in and probe the Red/Black wire of the sensor and see what voltage is coming from the sensor. With static A/C pressure voltage should be 0.8-1.0 volts.

INFORMATION.
On 2003 model year vehicles, a snowflake with a slash through it is shown on the display when the A/C has been turned off (by a press of the A/C button). The A/C can be turned on by pressing the AUTO button or pressing the A/C button again. This will remove the indicator from the display.


Owners of 03s may comment about poor A/C performance after they've pressed the A/C button and see what appears to be the snowflake illuminated on the display. What has actually happened, though, is that they have disabled the operation of the A/C compressor and the snowflake symbol, upon closer inspection, has a slash through it.

03 is the ONLY year like this.

[biggsteve97]

I was able to activate the compressor at the relay upon doing so also found a leak at the high side service port so now almost all the freon is gone. There is no power at the low side pressure switch. The diagram i have said the dark blue wire on the back of the control head is the signal wire for the switch. Problem is i have three dark blue wires on the back of the control head and none have power. I figured out that one of them is for a blend door. What color wire isthe signal wire actually supose to be for my year? I figued out the snowflake years ago though.
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[clinebarger]

With the switch plugged in (if it has above 22psi of pressure) the blue wire is grounded=No voltage. Unplugged or low pressure it should read 5 volts.

The low pressure switch signal is pin A12 on the light blue connector of the HVAC control head.

[biggsteve97]

I have no voltage on A12 with or without the low pressure switch connected. No voltage at low pressure connector with it unplugged.
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[clinebarger]

Originally Posted by biggsteve97

I have no voltage on A12 with or without the low pressure switch connected. No voltage at low pressure connector with it unplugged.
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Sounds like the control head is out.

[biggsteve97]

Thanks for the info. I was leaning toward the control head but with the other intermittent
Electrical issues i wasnt sure if it could be the body control module causing the problem.
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[biggsteve97]

Well installed a brand new control head last night and still have no voltage on low pressure wire. Really wish i had a gm tech scanner.

[clinebarger]

Check you 5 volt reference at B8, This can be a nightmare without a tech II.

[biggsteve97]

Ok, so I know this is not how its suppose to be done but did not have much choice since my dvom died. I used a jumper from B8 to A12 and the compressor still did not engage. I am trying to acquire another dvom soon but do not have much in the funds department at this time.

[lazerstrouts]

this truck wasnt a flood victim was it?

[biggsteve97]

not according to the carfax or the chevy dealer. but I do know the truck has had atleast two prior front end collisions. both were somewhat minor. The dealer did not know about the first one. I figured it out when I replaced the front bumper and it already had an aftermarket keystone bumper. I have recently found that the inner fender directly under the center of the Relay and Fuse center on the drivers fender is completely rusted through and the hole is a little larger than a golf ball. Its the only rust on the body so its weird that it is so centralized to me. The center looks good and so do all the wires.

[biggsteve97]

ok...update. Finally got a new fluke meter. I checked the voltage on B8 and it was 4.87 volts both with engine off and with engine running. When I get the Tahoe back from my friend this weekend I guess Ill reconnect my gauges and jump the relay to get the compressor to kick and double check my pressures. maybe the high side switch is bad and preventing the compressor from kicking on or my pressures are low again. Weird. I dunno what else it could be.

[biggsteve97]

Well this is annoying and a bit embarrising. Turns out the replacement control head is slightly different in how the ac works. That little snowflake that has the cross in it to show when the ac has been turned off. Well turns out that the replacement control heads snowflake does not have the cross in it and actually needs to be lit up now to show that the ac has been turned on. Why would gm change that let alone why would they not put a note in the box stating a design change. Oh well it works now but i have a slow leak and cannot find it. If its not one thing its another
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