QuestionSince the blower switch has a very smooth feel to it, and when it was working never showed any irregularity, I'm going to replace the VBC first. Can you provide the part number of the VBC? Thanks again.
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Thanks for your reply. I am sorry I did not originally specify that the blower speed is infinitely variable in this car. Apparently there is a solid state variable blower controller (VBC) in place of the resistor unit you describe. I'm thinking that your diagnosis is still correct, and that I need to replace the VBC. Yes/no? Thanks, Bob
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1990 Mercury Marquis with ATC. The blower only runs when the blower control is either set manually to high, or the auto selection choses high. No other speeds in between. Shop manual says to "check the ground wire from underneath the hood" but I can't I figure out from the manual which ground they are talking about or its location. The manual does say that when the blower runs at high speed, it uses its own ground, so that for any other speed, it uses this different ground. Any help will be greatly appeciated. Thanks, Bob.
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Very common problem Bob. Here's what I have on this.
The heater blower motor switch resistor has the following features:
The assembly is located in the engine compartment on the evaporator housing toward the center of the vehicle.
Three resistor elements are mounted on the resistor board to provide four blower motor speeds.
Depending on the heater blower motor switch position, series resistance is added or bypassed in the A/C blower motor circuit to decrease or increase A/C blower motor speed.
An overheating protective device (thermal limiter) will open the resistor coil when the temperature reaches 121°C (250°F) interrupting the blower motor operation in all speeds except HI.
The thermal limiter cannot be reset and is not serviceable.
Which means you'll need to replace it. It's $20 at the dealer part number E3AZ19A706A and book time calls for just 30 minutes to install.
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Well Bob, I found this also:
Article No. 90-8-11
AIR CONDITIONING - ATC - BLOWER MOTOR SPEEDS DO NOT CHANGE IN THE LOW TO HIGH SPEED RANGE OF AUTOMATIC OVERRIDE SETTINGS
FORD: 1990 CROWN VICTORIA
LINCOLN-MERCURY: 1990 GRAND MARQUIS, TOWN CAR
ISSUE: The blower motor speeds may not change in the low to high speed range of the automatic override settings. Also, the blower switch may exhibit a loose or mushy feel when moved up or down. This can occur if the blower speed potentiometer was damaged when it was manufactured.
ACTION: Install a new A/C control switch assembly. Refer to the following procedure for service details.
REMOVAL
1. Disconnect the battery ground cable.
2. Remove the control assembly from the instrument panel. Refer to the 1990 Lincoln Town Car/Crown Victoria/Grand Marquis Shop Manual, Section 36-75 for service details.
Figure 1
3. Refer to Figure 1 for a disassembled view of the control assembly.
4. Disconnect the wiring harness connector from the upper temperature control housing.
5. Remove one (1) screw attaching the switch to the control panel from the underside of the blower motor switch.
6. Remove the two (2) screws attaching the upper control housing to the control assembly.^ One of these screws secures the housing through an integral mounting bracket on the right side of the housing.
^ The other screw attaches the housing through an integral mounting bracket on the rear side of the housing.
7. Remove the blower switch knob.
8. Push rearward on the blower switch lever to clear it from its slotted opening in the control assembly.
9. Lift the blower switch and temperature control housing away from the control assembly.
NOTE: WIRING FOR THE BLOWER SWITCH LINKS IT WITH THE CONTROL HOUSING. THEREFORE, THE TWO PARTS CANNOT BE REMOVED SEPARATELY. SEE FIGURE 1.
INSTALLATION
1. Position the new A/C control switch assembly and temperature control housing where they assemble to the control assembly, Figure 1.
2. Install the three (3) screws which hold the switch and housing to the control housing.
3. Connect the wiring connector to the temperature control housing.
4. Install the control housing into its opening in the instrument panel. Refer to the 1990 Lincoln Town Car/Crown Victoria/Grand Marquis Shop Manual, Section 36-75 for installation details.
5. Connect the battery ground cable and check the system for proper operation.
PART NUMBER PART NAME CLASS
FOVY-19986-B A/C Control Switch B
OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: Eligible Under Basic Warranty Coverage
OPERATION DESCRIPTION TIME
90081 1A Replace Switch 1.0 Hr.
DEALER CODING
BASIC PART NO. CONDITION CODE
19986 42
OASIS CODES: 2600, 2610, 2611, 2632, 2633
Unfortunatley, I can't send pics in this media. I also found:
The solid state Variable Blower Controller/high Blower Relay (VBC) converts low current signals from the Automatic Temperature Control (ATC) module to a high current, variable ground feed to the blower motor. The blower motor speed is infinitely variable and is controlled by the ATC control module software. A delay function provides a gradual increase or decrease in the blower motor speed under all conditions. When the ATC control module signals the VBC to maximum blower speed, a relay bypasses the solid state control and provides a direct path to ground for the blower motor.
CAUTION: The system should not be operated with the blower motor disconnected. Damage may occur to the VBC if cooling air is not provided through the evaporator assembly.
AnswerHi Bob!
Here ya go:
REMOVAL
Disconnect the wiring harness connector from the Variable Blower Speed Controller (VBSC) assembly.
Variable Blower Speed Controller (VBSC)
Remove the two VBSC assembly retaining screws securing the VBSC board to the evaporator case assembly.
Remove the VBSC assembly.
INSTALLATION
Position the VBSC assembly in the opening in the evaporator case assembly.
Install the two VBSC assembly retaining screws and tighten.
Connect the VBSC wiring harness and check the blower for proper operation.
Bob, I have looked everywhere to get the part number for you. I have a picture of it, location of it, but just can't find the dang part number. Sorry.
