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AC Problem

Nash

By Nash
in Ask A GM Technician

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Nash Enthusiast

Nash

Posted
Posted

First post so please bear with me. I recently purchased a 98 Z71. Love the truck, but found a recent problem. The AC works, but not when the transmission is in Drive or neutral. If the Transmission is in any other gear or park, the AC compressor kicks on. As soon as it is put into drive, the compressor clutch cuts off. Has anyone had a similar problem? I'm stumped. :chevy::D

mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted

Did you check *all* your fuses?

 

If the fuses all check out listen for circuit breakers clicking. Key on, engine not running, trans in D.

Nash Enthusiast

Nash

Posted
  • Author
Posted
Did you check *all* your fuses?

 

If the fuses all check out listen for circuit breakers clicking.  Key on, engine not running, trans in D.

 

 

 

 

Fuses all check out fine. I can't hear any circuit breakers, only the compressor clutch as it kicks on and off.

Nash Enthusiast

Nash

Posted
  • Author
Posted
Did you check *all* your fuses?

 

If the fuses all check out listen for circuit breakers clicking.  Key on, engine not running, trans in D.

 

 

 

 

Fuses all check out fine. I can't hear any circuit breakers, only the compressor clutch as it kicks on and off.

 

 

 

 

 

I double checked the fuses again this morning, and listened for the circuit breakers as suggested (truck not running. Key in the on position, and transmission in D). The only thing I hear kick on is the fuel pump. I am at a loss as to what is causing this. Could the Park/Neutral switch adjustment cause this? :chevy:

ChevyTech007 Enthusiast

ChevyTech007

Posted
Posted

You need to find out if your loosing power or ground when it is inop. It grounds a G105 at the lower right front of engine. When its in D or R use a test light at the compressor clutch connector to see what you don't have. Then post back.

Nash Enthusiast

Nash

Posted
  • Author
Posted
You need to find out if your loosing power or ground when it is inop. It grounds a G105 at the lower right front of engine. When its in D or R use a test light at the compressor clutch connector to see what you don't have. Then post back.

 

 

 

 

I checked with the test light as suggested. No power at the compressor clutch connector when the truck is in D or N. I do have have power when in the truck is in P, 3, 2, or 1. What can cause this?

Nash Enthusiast

Nash

Posted
  • Author
Posted

Does anyone have an idea what may be causing this. It is really frustrating me. I don't want to go into the summer having to drive in 3rd gear just so I have AC. Why would the compressor work in every gear except D and N?

ChevyTech007 Enthusiast

ChevyTech007

Posted
Posted

This is a VERY long shot but you might want to look under the under-hood fuse block. I have seen rodent damage on a few. They just love it under there. Only other thing you could do is take it to a dealer and have them scan to see if you are loosing compressor request from the control head.

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted

The first step in figuring this one out is understanding how the system operates. The PCM/VCM controls the a/c compressor via a relay and will turn it on or off based on a variety of inputs. The park/neutral switch is not one of them as far as I can tell.

 

So it'd be really handy to have a scanner hooked in to look at various parameters and their readings in P/N/D/1, etc., etc. Do you lose A/C request to the PCM when put in D or is the PCM still getting the request but inhibiting clutch engagement for other reasons.

Nash Enthusiast

Nash

Posted
  • Author
Posted

Thanks for the reply. I don't have the $ to take this to the shop right now, so I tried some trouble shooting. I used a jumper wire on the pressure switch and ran the Tranny through all of the gears. I thought maybe the pressure switch was telling the computer that it had a pressure problem (low R134) when it was at lower RPM's. Anyway, it had no affect. The compressor clutch still did not operate in D or N, but it did in all other gears. In addition, I swapped the AC and Starter Relays with no affect on either.

 

Are there any other things I could check without taking this to the shop (what other imputs does the computer look for). This seems like it should be something really simple.

 

As a side note, I noticed that the shift indicator lights at the dash do not work in D or N. They work in all other gears. It's a long shot, but could this be related?

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted
As a side note, I noticed that the shift indicator lights at the dash do not work in D or N.  They work in all other gears.  It's a long shot, but could this be related?

 

 

 

 

I have no doubt it's related. Does it start normally in only park/neutral?

 

This may be a neutral switch problem. I'm not sure what the PCM is seeing that might cause it to inhibit a/c operation, but it may do so in confusing gear position signals.

 

I'd look to the neutral switch. Note that they use some sort of goo to seal the connector and the only way I've found to get it disconnected is to heat it severly with a heat gun first. A GOOD hair dryer may do it, but I don't know if that can get it hot enough.

jhm Senior Enthusiast

jhm

Posted
Posted

If you don't have cash to go the dealer, maybe Autozone or another parts store can check the codes for you. Around here they do it for free. Might help.

Nash Enthusiast

Nash

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GM-Tech,

Thanks for the info. After it stops raining, I will go out and see about the park safety switch. It seems to operate correctly as far as I can tell (The truck will not start in any gear except park or neutral). However, I have some suspicions that the previous owner had the transmission out of this truck. That's not necessarily a bad thing, but maybe they did not get everything hooked back up correctly.

 

jhm,

The Autozone does free code checks here as well. I may go down and see if they can pull any codes.

Nash Enthusiast

Nash

Posted
  • Author
Posted

OK. I replaced the Park/Neutral safety switch with a new one. Still No AC or indicator lights in D or N. I checked all of the electrical connections for chafing or other signs of wear, and could not find any problems. After I changed the Park Neutral switch, the service engine soon light came on. I went to Autozone, and had the codes pulled. P0740, and P1860 were showing. I can't find these two codes in my Hanes manual. I know that the P0740 is the TCC circuit, and the P1860 deals with the transmission. However, that is all I know. I do not know what the TCC circuit is, and I was told that I would have to consult the dealer for code P1860. Does anyone know what these codes mean, and would they have anything to do with my AC and Gear indicator problem?

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