Question about heater?

88GT 5pt0 · 01-21-2004, 10:45 PM

My heater only works when I put it on the highest fan setting and the defroster doesn't at all. What might be wrong with it and how do I go about fixing it? Theres also a lot of cold air comming out under the dash on the passenger side when its on. Also it seems to be really draining the power because whenever I put it on the headlights and the dash lights dim. I have a system but it doesnt cause the lights to dim, even with the system off the heater makes the lights dim. I plan on putting in an alternator from a 94 soon

420nitro · 01-21-2004, 10:55 PM

If it only works on hi, then I would check the blower fan switch first. As goes for the blowing in cold air where it doesn't supposed to then also check for vacuum leaks under the dash by the control panel and make sure you don't have a break in the little vacuum tee on the fire wall on pass. side. in the engine conpartment (not the big vacuum tee by the brake booster.)
Good luck

88GT 5pt0 · 01-22-2004, 03:02 AM

Where is the switch located? Im goin to the junk yard soon for an alternator maybe I can get that too

Maroon 5.0 LX · 01-22-2004, 07:34 AM

I believe there is a fan resistor, that when it goes bad, reverts to Hi-speed only. Not sure where it is located, check a shop manual.

LX5liter · 01-25-2004, 11:11 AM

The hi speed only problem is probably the resistor like Maroon said. It should be located in the duct that brings in outside air into the heater core. They usually put it there for cooling. It may be under the dash in the ductwork. Usually held in by two screws.

84LX89GT · 01-27-2004, 03:15 AM

I'm gonna say blower motor resistor (usually located on the passanger side plenum underneath the dash - should have a few wires running to it) It is square with one bolt holding it is usually tan in color. When on high, the blower motor resistor is bypassed so that's why your fan still works. It's normal for the resistors to go bad since air is being blown over them all the time (cooled by the blower motor) and if there's moisture in your distribution plenum it gets on the resistor.

01-21-2004, 10:45 PM	#1
88GT 5pt0 Registered Member Join Date: Jun 2003 Location: Chicago Posts: 73	Question about heater? My heater only works when I put it on the highest fan setting and the defroster doesn't at all. What might be wrong with it and how do I go about fixing it? Theres also a lot of cold air comming out under the dash on the passenger side when its on. Also it seems to be really draining the power because whenever I put it on the headlights and the dash lights dim. I have a system but it doesnt cause the lights to dim, even with the system off the heater makes the lights dim. I plan on putting in an alternator from a 94 soon __________________ My Cardomain Website

01-22-2004, 03:02 AM	#3
88GT 5pt0 Registered Member Join Date: Jun 2003 Location: Chicago Posts: 73	Where is the switch located? Im goin to the junk yard soon for an alternator maybe I can get that too __________________ My Cardomain Website

01-22-2004, 07:34 AM	#4
Maroon 5.0 LX Registered Member Join Date: Mar 2001 Location: Southern Maryland Posts: 471	I believe there is a fan resistor, that when it goes bad, reverts to Hi-speed only. Not sure where it is located, check a shop manual. __________________ '89 LX 5.0 - 5 speed. Original Owner '94 E-150 4.9 Hi-Top Conversion Van '06 Mustang V-6, 5 speed

01-25-2004, 11:11 AM	#5
LX5liter dude5l Join Date: May 2001 Location: Grande Prairie, Alberta, Canada Posts: 603	The hi speed only problem is probably the resistor like Maroon said. It should be located in the duct that brings in outside air into the heater core. They usually put it there for cooling. It may be under the dash in the ductwork. Usually held in by two screws. __________________ Good luck! Brad R. 1992 L.X. 5.0 coupe MODS: A few little bolt ons New Best time ...11.60 @ 128 mph @ 2000+ ft altitude. Rice Haters Club member #39 Users rides #2542

01-27-2004, 03:15 AM	#6
84LX89GT Mustangs Join Date: Jul 2000 Posts: 1,938	I'm gonna say blower motor resistor (usually located on the passanger side plenum underneath the dash - should have a few wires running to it) It is square with one bolt holding it is usually tan in color. When on high, the blower motor resistor is bypassed so that's why your fan still works. It's normal for the resistors to go bad since air is being blown over them all the time (cooled by the blower motor) and if there's moisture in your distribution plenum it gets on the resistor. __________________ 2005 Suzuki Hayabusa GSX1300-R 1980 Ford Thunderbird - 255 V8 ported heads, 5.0L ported stock headers, O.R. H-pipe and Flowmaster 2-chambers, dual roller timing chain hi-po Mack Truck hood emblem 1985 Mustang GT 5.0L T5, F-303, GT40p, headers, off-road h, flowmasters, MSD stuff, etc. Sold 02/06/04 1989 Mustang GT ET: 13.304@102.29 mph (5-24-03) Sold - 1998 Mustang Cobra coupe, 1/4 mile - street tires: 13.843@103.41 (bone stock)

01-21-2004, 10:55 PM	#2
420nitro Registered Member Join Date: Nov 2003 Location: Rockford Posts: 596	If it only works on hi, then I would check the blower fan switch first. As goes for the blowing in cold air where it doesn't supposed to then also check for vacuum leaks under the dash by the control panel and make sure you don't have a break in the little vacuum tee on the fire wall on pass. side. in the engine conpartment (not the big vacuum tee by the brake booster.) Good luck

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