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MCVGreg
MCVGreg, Master Troubleshooter
Category: Car
Satisfied Customers: 6299
Experience:  25 + Years Working with Cars & Electronic Control Systems
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have a 99 gmc jimmy..........blows only outside vent ...

Customer Reply

Customer: replied 7 years ago.
have a 99 gmc jimmy..........blows only outside vent air..........blower works..........but no a/c or heat.........is it the controller?   Have already checked the fuses....both in the car and under the hood
Expert:  MCVGreg replied 7 years ago.

HiCustomer Thank you for asking your question on Just Answer.

Are you saying that you have TWO problems
1 - AC compressor does not run unless jumpered to power and
2 - Mode control doors (which switch between dash vents and floor vents) will only blow out the floor vents?

Also, is the a "manual" or "Automatic" AC system (automatic is where you have a "set temperature" - usually a digital display)

Take Care, Greg A.

Customer: replied 7 years ago.
No i believe it is one problem......2 symptoms
Has nothing to do with the vent doors....i am saying neither the ac or the heat works in the car........the mode control doors cycle in all modes.......but no ac and no heat no matter where you set the heat/cold knob....this is a manual system as it does not have a digital display on the control system.
Expert:  MCVGreg replied 7 years ago.

So the blower blows air through the dash vents, floor, or both depending on the mode switch - Right?

Is the AC compressor coming on at all?

Customer: replied 7 years ago.
No ac compressor does not cycle at all...........and yes. the mode switch works in all positions..........but no heat or cold only ambient air
Expert:  MCVGreg replied 7 years ago.

I assume you want to get the AC going first?

Has the refrigerant charge been checked recently? I know you jumped directly to the compressor, but if it is just slightly low, the pressure sensor will keep it from coming on.

Customer: replied 7 years ago.
Jumpered the low pressure switch....so that can't be the problem.........
Customer: replied 7 years ago.
Checked the refrigerant pressure with guages.......pressures for ac system are fine........something is not allowing the ac and heat not to work at the same time........what is there in the system that can do that?
Expert:  MCVGreg replied 7 years ago.

Hi again,

Here is a diagram related to the AC compressor control. You will notice there is a reference to the ECC (Electronic Climate Control) module. I will take a look at that.

In the mean time, I would suggest that possibly the fuse(s) or relays may be suspect (upper left of diagram). If those are working OK, I think we will be looking at the ECC.

graphic

Let me know if you discover anything while I am looking up the ECC.

Take Care, Greg A.

Expert:  MCVGreg replied 7 years ago.

Oops - I clicked on the automatic system. You can ignore that last answer.

Give me a couple of minutes to get it the right one.

What Engine do you have (2.2 or 4.3 liter)

Customer: replied 7 years ago.
Reply to MCVGreg's Post: Have already checked the fuses and relays..........switched out relays......can you tell me where the ecc module is located on the vehicle.........?
Expert:  MCVGreg replied 7 years ago.

I will take a look, but I think that was on the "automatic" AC system.

By the way, is this a 2 orXXXXX It might make a difference.

Also, what is the engine size?

 

Customer: replied 7 years ago.
XXXXX
Expert:  MCVGreg replied 7 years ago.

What engine size? (2.2 liter or 4.3 liter)

 

Customer: replied 7 years ago.
4.3...........six cylinder
Expert:  MCVGreg replied 7 years ago.

OK. I don't think you have automatic AC (from what you have said) but here is the location:

ECC Module Location (with Automatic AC): The IP harness center of the IP, below the radio.

graphic

Expert:  MCVGreg replied 7 years ago.

OK - I think we are getting closer.

Here is the diagram for AC Compressor control for your vehicle. I will get you a diagram for the location of the VCM (Vehicle Control Module), if you need it. It is under the hood. and has 4 connectors on it.

graphic

 

Expert:  MCVGreg replied 7 years ago.

Here is the location of the VCM and the connectors. Look for loose connections.

I would also try jumpering the compressor relay control to ground and see if the compressor comes on. That would verify that everything is working (fuse, relay, etc.).

If that makes it work, we will have to go backwards towards the switches inside the cabin.

graphic

Take Care, Greg A.

Customer: replied 7 years ago.
ok...........sorry i haven't been able to get back to you sooner........but the internet went down for a couple of hours.......i do not think the electrical diagram you have given me is for a 99 Gmc Jimmy as my control on the dash does not have a bilevel switch.......on ac max and ac and then the positions for the vents and defrost...the temp is only controlled by the hot cold reostat type switch......
Expert:  MCVGreg replied 7 years ago.

Sometimes the diagrams in the manual are "generic" and will not exactly match what you have. I have also found mistakes in the manuals some times.

What I show is what I have for the 99 Jimmy Manual AC 4.3 literXXXXX

 

Customer: replied 7 years ago.
well hopefully the wire colors are right.......so i can trace out the system........
Expert:  MCVGreg replied 7 years ago.
Let me know what you find.
Customer: replied 6 years ago.
Reply to MCVGreg's Post: found problem.............wire off behind the compressor...........duh......lol
Expert:  MCVGreg replied 6 years ago.

Hi Bob.

I'm glad you found it. Congratulations!

Did I help enough for you to Accept an answer?

Thanks, XXXXX

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MCVGreg
MCVGreg
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25 + Years Working with Cars & Electronic Control Systems