Goblin1488

First off I would like to say hello to all forum members. I'm new and glad to be on here now!

Side note- I've read over 200 articles on this A/C system and studied schematics and from what I have read from this forum and others is that many silverado owners with comparable year make and model are having similar issues to what I am experiencing. many blogs and forum threads I have read were started before doing the research and putting the time in. I decided to post this as last resort because I have spent far too much time and money on the A/C in this truck and would like to just be done with it! I always do my research and normally can solve my own problems without asking for advice. But I am no mechanic or electrician and I would like to thank anyone for their input in advance.


Specs: 2003 Silverado LS 1500
5.3L V8
4wd automatic
(Dual manual HVAC climate control)

History- I bought this truck last year and have been doing the repairs ever since. The owner before me had only had it a short while and couldn't tell me much about the work that had been done to it before he got it. He told me the A/C needed to be charged and that it should work. He lied. The heater core/Evaporator core housing had been cut to expose the Evap core. Reason for this was the supercharger placement called for the Evap core to be moved temporarily to bolt on the blower. The air diversion was working fine but A/C system was empty. After replacing the leaky Evap core and then replacing the housing. Removing the housing is said to be a 9 hr job for a GM tech and cost 1500$ in labor. It took me 4 days. During this I realized that the housing I got at the junkyard was for regular climate control and not dual. But it took so long to find and was so hard to remove that I installed it anyway. The only difference was it had one less actuator and the connection between the dash vents and housing was one duct instead of two. I charged the system and checked pressure (hi pressure/low pressure) this was done with the help of an A/C mechanic friend of mine so everything was done correctly. Clutch would not engage.

Then...Jumped the A/C comp relay to bypass the ground on low side (PCM to relay). clutch engages and blows cold. From this I determined That high side of the circuit has continuity from climate control module to relay. So the problem is That the signal either isn't getting TO PCM for AC on from the control in the dash, or isn't SENDING ground signal to relay to complete circuit.

What I've done:

• checked all connections and made sure all wires are plugged all the way in (going in and coming out) at junctions between climate control module, SDL, BCM, and PCM.
•Tested all relays and fuses for hvac
• inspected wire harness for beaks or melting

This system is a bit complicated for someone who is just starting to learn to work on cars, and there is a couple things That confuse me. In the schematic the blower motor resistor seems to be on the same circuit as the actuators and wired into the same fuse that controls the actuators in the vent doors, but some article I've read point the finger at the resistor for the causing the clutch not to engage. But this was in the auto temp control models. Mine is manual dual climate control w/ rear window defeost In these models the outside ambient air temp sensor controls the auto climate. But on my truck I have the temp and compass reading on the rear view mirror in the cab. Since it doesn't control anything and just gives me a reading it shouldn't have an affect on the AC circuit, or should it? Also, the whipple supercharger is wired into the PCM, and the check engine light to stop the truck from thinkin the fuel trends are off. The charger is not pigtailed to any wires coming from or going to PCM on the hvac circuit. But I've read that some codes in the PCM can cause the ground not to be sent to engage clutch. I cannot find what codes to look for. And lastly I want to test my snowflake button on the climate control module to see if it is sending the signal to the PCM before I buy a very expensive part that did not need replacing. How would I go about this.

I know this is a very technical post and very long, but I am overwhelmed and would really appreciate any help I can get. I can't go another summer in 115 degree heat with no A/C. I would like to get the clutch to engage when I hit the button on the controls without using a toggle switch to ground the relay at pin 85.

Again, thank you for any help.

cleveland63b

i havent looked into diagrams or anything yet but it seems simple to me...you jump the relay and it works and the relay is controlled by the PCM? Either the relay or pcm driver is bad

Goblin1488

If only it were that simple I'd be long past this issue. The PCM receives Donald from everywhere. A/C switch ext. and there are other codes that have little to do with the A/C that can prevent PCM ground signal from being sent

cleveland63b

codes? never mentioned codes...