Allpar Forums banner
21 - 30 of 30 Posts

·
Super Moderator
Joined
·
33,708 Posts
Does it blow as soon as you put a fuse in, with key off, or when you turn the key on, engine off, or engine running, or when you turn A/C on?
Do you have an owners manual to tell what is on that fuse?
 

·
Registered
Joined
·
5,452 Posts
. . . .This prompted me to trace and test the wiring from the A/C fan switch in the dashboard. There is a solid Brown wire that should carry voltage to the Low A/C switch on the accumulator and I was getting 0V there as well. I am getting 0V at the A/C fan switch in the dashboard as well. . . .
That BR / brown wire does NOT carry voltage to the low pressure switch on the accumulator. It provides a ground sense to the PCM for operation of the compressor clutch relay. The ground path travels through the low pressure switch and the high pressure switch. If path grounded with engine running and the refrigeration system is in proper design pressure range ( not too high, not too low) the PCM will ground the A C clutch relay and energize the compressor clutch. The ground path goes through the HVAC control. Also the HVAC provides a separate, unique ground path for the climate control blower fan. See attached image. I have added some color dots so you can trace the electrical logic flow for the multi-throw, double throw fan switch which provides unique ground paths to common ground G203.

Slope Rectangle Schematic Line Font


. . . . Yes it blows right as it makes contact in the fusebox. I tested with key on, engine off, with A/C on. Here's what the owners manual shows for that Fuse 12 (see picture) . . . .
Note that the wiring diagram on 8W - 11 - 14 shows fuse #12 in the fuse block under the instrument panel as providing power to the BTSI / brake transmission shift interlock solenoid, the A C compressor clutch relay (control side), low speed radiator fan relay (control side), high speed radiator fan relay control side.

Try this test. Ignition key switch in RUN position. Remove the A C compressor clutch relay, low speed radiator fan relay, high speed radiator fan relay. Insert good fuse in slot #12 in its respective location under instrument panel. Does the fuse fail? If YES then a short to ground exists in the wiring from the #12 fuse to the BTSI or the BTSI itself.

If NO then insert known good relay into position in the PDC for A C clutch. Does fuse fail? If YES then short to ground in circuit from fuse #12 to A C clutch relay (control side).

If NO then move known good relay into position in the PDC for low speed radiator fan. Does fuse fail? If YES then short to ground from fuse #12 to low speed radiator fan relay (control side).

If NO then move known good relay into position in the PDC for high speed radiator fan relay. Does fuse fail? If YES then short to ground from fuse #12 to high speed radiator fan relay (control side).[/QUOTE]
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #24 ·
My apologies folks - the fuse seems to have been blowing because of the way I setup the relay to test. Once I removed the test wires and plugged in the relay normally the fuses stopped blowing.

So now I am back to the original issue - the Fan does not turn on when I activate A/C.
 

·
Registered
Joined
·
5,452 Posts
. . . . . So now I am back to the original issue - the Fan does not turn on when I activate A/C. . . . .
You are at the point in time where you need the services of a professional repair facility. Find a shop with a bidirectional scan tool. Under special functions of the tool a command can be issued to the PCM to energize the low speed radiator fan relay and the high speed fan relay. If the fan speed responds accordingly that proves the PCM can control the relays. At the same time monitor engine coolant temperature.

If one or both relays click but no fan operation the PCM can control the relays but there is a problem with load side circuitry to the fan motor including the fuses. If the relays do NOT click when command activated with scan tool the problem is either wiring to the control side of the relays or an internal problem with radiator fan drivers in the PCM. But failure of the PCM should only be considered when all other tests lead to a PCM fault.
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #26 ·
Thank you @AllanC

I am going to run some tests/probes on the relays/PDC once again now that I have replaced the fuses and they are not blowing.

Just to be sure.

Ifthings are inconclusive after that then I'll resign myself to going to a shop.

Shane
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #27 ·
Here are the results of my tests today with all fuses good (not blown):


Key off, engine off, AC OFF
Low Speed Relay:

30 = 12V
86 = -0V
85 = nothing
87 = -0V (fan turns on when I apply power with probe)

High speed Relay:
30 = 12V
86 = nothing
85 = -0V
87 = -0V (fan turns on when I apply power with probe)


Key On, engine off, AC OFF
Low Speed Relay:

30 = 12V
86 = 12V
85 = nothing
87 = -0V (fan turns on when I apply power with probe)

High speed Relay:
30 = 12V
86 = -0V
85 = 12V
87 = -0V (fan turns on when I apply power with probe)



Key On, engine off, AC ON
Low Speed Relay:

30 = 12V
86 = 12V
85 = nothing
87 = -0V (fan turns on when I apply power with probe)

High speed Relay:
30 = 12V
86 = -0V
85 = 12V
87 = -0V (fan turns on when I apply power with probe)



Key On, engine ON, AC ON
Low Speed Relay:

30 = 12V
86 = 12V
85 = -0V
87 = -0V (fan turns on when I apply power with probe)

High speed Relay:
30 = 12V
86 = -0V
85 = 12V
87 = -0V (fan turns on when I apply power with probe)

A previous post suggestion said: "If you close the relay and measure between contacts 86 and 85, you will have nearly 0V. If you measure 86 to a ground, you have 12V. If you measure 85 to a ground, you have 0V."

I got these results except that when I measured 85 to a ground I got 12V.


So with all these results I still have the main issue of no fan turning on with A/C. Perhaps it is time for a pro repair technician...

Thanks,

Shane
 

·
Super Moderator
Joined
·
33,708 Posts
If you measure 12V from pin 85 to ground, it means the relay is actually open. Pin 85 is the negative coil contact, and the PCM switches it from 12V to ground to close the relay. The positive relay coil contact (pin 86) is at 12V whenever the key is on, and if you have 12V at the negative coil contact, the coil is not energized and the relay stays open. When you pull pin 85 to ground, the coil is energized and the magnetic field that results will close the relay.
 

·
Registered
Joined
·
5,452 Posts
. . . .So with all these results I still have the main issue of no fan turning on with A/C. Perhaps it is time for a pro repair technician.. . . . .
I will repeat the criteria which the PCM uses to operate the radiator cooling fan for low speed and high speed.

Rectangle Font Parallel Number Magenta


Note no mention is made that activating the A C clutch causes the radiator fan motor to energize in either low or high speed operation. The criteria used is engine coolant temperature and vehicle speed.

When you made all of your voltage tests, was the engine at high operating temperature? If less than the thresholds specified in the chart the PCM will not ground the low speed and / or high speed fan motor relays.

You can let the engine idle and watch the temerature gauge. When the gauge needle gets to the 3/4 mark (close to the H) does the radiator fan start running. But the temperature gauge is not calibrated so there is no way for you tio know the exact engine coolant temperature. So that is why the suggestion was made that you are going to need to find a shop with a bidirectional scan tool and determine if the PCM will receive a command from the tool and activate the radiator fan relay. At the same time the scan tool can display engine coolant temperature. You have to know the parameters that are being used to determine if there is a problem with the PCM not energizing the radiator fan relays.
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #30 ·
Thank you @Bob Lincoln and @AllanC

My tests/numbers yesterday were done with the relays pulled and the engine was not warmed up - so probably not very helpful.

Today I will warm the engine up (I have an Autometer temp gauge installed which may help me know when it is at or above 180 degrees) - which from the chart @AllanC shared should be when the High Speed fan is activated with the AC on.

Much appreciated,

Shane
 
21 - 30 of 30 Posts
Top