NO heat, only cold air!!

Chris_H · 12-27-2002, 12:07 AM

Ok, here is the problem. About 4 months ago, the air conditioning would only blow out the defrost vents, regardless of what setting I had it on. It would also only blow on high. I replaced the HVAC controls and I have the same problem with it only coming out the defrost vents, but I can control the fan speed now. The other problem is, it only blows cold air. The heat won't work. I know the heater core is good, but no matter what, it will only come out the defrost on cold. Anybody ever had this problem before?? We have actually had snow this year and its kind of rough driving with frozen windows. Any help is greatly appreciated.

Chris

crazypete · 12-27-2002, 12:17 AM

This so totally sounds like the flaps inside the heater assembly arent switching. If you dive under your dash and follow from above the radio back along the vent, you'll see these "drums" with vacuum lines going to them. There's a little flap that gets opened and closed by a lever right where you're looking and this lever is actuated by the vacuum drum. This baby redirects air to either the vents or the windshield. There's a second flap sort of behind the glovebox that switches from the heater core passage to the a/c and heater passage. I think this one is cable actuated. There's also a third flap by the passenger side kick panel that directs air down.

When you turn the selector knob, do you hear a hiss....creak....flap? You should. If it's not switching, you may have a leak in one of those lines. They end in the back of the control knob unit. I'm not positive where the vacuum comes from, actually, but it does work with the engine off.

Fox Body · 12-27-2002, 12:19 AM

concerning where the heat comes out, lift the hood and check to see if the small, hard plastic, black vacuum line by the firewall, on the passenger side, is apart. It should be over where the hoses go to the heater core, but right up against the firewall. It is possible that that line has come loose. Reconnect and this will give air to vents instead of just floor and defrost.

Concerning the no heat, all I can think of is that if your heater core is good, you need to check and see if that when you set the heater from cold to hot, that it is actually doing something. It will be hard to see/find, but see if you can somehow see if when you change the setting from cold to hot, there should be a wire (almost coathanger wire thick) that draws a door closed. That is what sets it to heat. If that wire is somehow disconnected, then it is not pulling the "door" or "flap" shut. That is definately one reason that could be the problem. That wire is also held to the flap with a plastic

piece and if that piece has broken, then the wire isn't connected to the flap and if it has been previously set to cold, then you won't be able to draw it back and, therefore, no heat. That is what is actually wrong with my car. So I just leave it on hot setting. I know I may be being kinda vague, but that's really all I can think of now (This is if the core is fine). Hope it helps a little.

Chris_H · 12-27-2002, 12:30 AM

I can't believe that I didn't even think to check that door for the air. I had that problem last year, but its because the gears in the control knob were worn out. i will also have to check that vacuum line tomorrow. I didn't even know there was one for this. Thanks a lot. I'll let you know how it goes.

Chris

93blkGTfun · 12-27-2002, 01:44 AM

I had the exact thing happen in my stang. The plastic vacuum line under the hood was broken. It was the one that is connected to the one that says A/C on the tee on the driver's side of the firewall.

Chris_H · 12-27-2002, 07:09 PM

No such luck. Got up under the dash today when I got home from work. All the lines are hooked up, the temperature "wire" is opening the door like it should, and all the vacuum lines under the hood are good. I even have the boost gauge line spliced in with the A/C line, and the boost gauge works. Should that be spliced into the A/C line? I just got to thinking if thats a good idea or not.... Any other suggestions? If not I have about had it. I have a commuter car and I will rip this whole A/C system out before I lose my mind with it. I'll just deal with the 110* in the summer and the ice on the windows in the winter when I do drive it.

Chris

84LX89GT · 12-30-2002, 07:14 PM

Defrost is a default setting for the heater system for when there is a vacuum problem. Did you check for vacuum from the lines at the vacuum motors (the drum things). There should be a fresh air/recirculate door for when max A/C is off/on, a condensor/heater core door for heat selection, a defrost door and a vent/floor door. Because of the fact that you can't change Heat OR the location that sounds like to me you don't really have a vacuum distribution problem, but rather a supply problem. Check at the heater control unit to see if vacuum is getting to the control unit (the thing with knobs you turn), if not trace that to the vacuum tree on the firewall. One thing it also may be is that there is a vacuum reservoir for low vacuum conditions (such as wide open throttle, heavy throttle conditions). If you have a large leak for the reservoir vacuum circuit it may cancel vacuum to the door supply system.
First i'd just check and see if vacuum is actually getting to the control unit, if not then check at the tree where the line is, if so i'd trace along that vacuum line and see if there are any splices/alternate paths it may follow. I forget off the top of my head where the reservoir is spliced into, but if you need the info i can look it up.
Good luck, keep us posted.

Chris_H · 01-01-2003, 10:56 PM

Well I have checked the lines at the tree on thr drivers side, and the lines going into the firewall on the passenger side. I don;t see anything wrong with the vacuum lines. This is getting to be a pain in the butt, and not even worth my time anymore. To me, the next step is to rip everything out and lose the weight. After all, who needs a/c when it gets to be over a 100* during the summer.

Chris

HotRoddin · 01-01-2003, 11:30 PM

Quote:

Originally posted by Chris_H
I don;t see anything wrong with the vacuum lines. Chris

Just because the vacuum lines look ok doesn't mean there is vacuum present... check and see if there is vacuum at those points ... you could have a hose loose somewhere and the lines would still look ok right ! vacuum ... check the vacuum ... there could be a hole in one of the vacuum cans ... any one of a dozen places you could be losing it .... start right at what moves the flap ... if no vacuum there keep moving back until you find where you're losing it.

Chris_H · 01-01-2003, 11:40 PM

Ok, what is the best way to check for a vacuum leak? Will I feel it, hear it, something I can spray around it to see if it's leaking? Sorry, just don't know the best way to find a leak.

Chris

HotRoddin · 01-01-2003, 11:55 PM

You should be able to feel it .. pull the line off and hold your finger over it, or put it to the edge of your lip (more sensitive) then actuate the control ... you should feel the suction.

84LX89GT · 01-02-2003, 05:32 AM

HotRoddin is correct you will be able to feel it with your finger on the vacuum line and you'll also probably be able to hear it as well with the line disconnected, also make sure that the line your checking at has the door control knob in the correct setting (if you're not sure just tinker around with the settings until (if) you set something).

Unfortunately this is one of those things that may not have an easy answer except for arduous step by step diagnosis.

Chris_H · 01-02-2003, 10:37 PM

Ok scratch everything that was said above. just found out today that the heater core is leaking for sure. Started to smell antifreeze, and sure enough its coming out the little drain hole. I have changed it 2x already, not in the mood to make it 3rd times the charm category. Thanks for the help, sorry to give up on it, but I am just not in the mood for it. The car is slowly becoming more of a weekend driver anyway. Take care.

Chris

12-27-2002, 12:07 AM	#1
Chris_H Registered Member Join Date: Oct 1999 Location: New Mexico Posts: 488	NO heat, only cold air!! Ok, here is the problem. About 4 months ago, the air conditioning would only blow out the defrost vents, regardless of what setting I had it on. It would also only blow on high. I replaced the HVAC controls and I have the same problem with it only coming out the defrost vents, but I can control the fan speed now. The other problem is, it only blows cold air. The heat won't work. I know the heater core is good, but no matter what, it will only come out the defrost on cold. Anybody ever had this problem before?? We have actually had snow this year and its kind of rough driving with frozen windows. Any help is greatly appreciated. Chris __________________ 1987 LX, Best times: 13.47 @ 102.49, 1.80 60ft 6900' DA

12-27-2002, 12:17 AM	#2
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	This so totally sounds like the flaps inside the heater assembly arent switching. If you dive under your dash and follow from above the radio back along the vent, you'll see these "drums" with vacuum lines going to them. There's a little flap that gets opened and closed by a lever right where you're looking and this lever is actuated by the vacuum drum. This baby redirects air to either the vents or the windshield. There's a second flap sort of behind the glovebox that switches from the heater core passage to the a/c and heater passage. I think this one is cable actuated. There's also a third flap by the passenger side kick panel that directs air down. When you turn the selector knob, do you hear a hiss....creak....flap? You should. If it's not switching, you may have a leak in one of those lines. They end in the back of the control knob unit. I'm not positive where the vacuum comes from, actually, but it does work with the engine off. __________________ 91 GT Carb conversion, holley 600 double pumper, edelbrock performer intake, FMS "C" drop springs, march 1000 underdrive pullies, crane 1.7 roller rockers, GT-40P headers, bassani x pipe, american thunder catback, FMS 4.56's, msd aL6, trunkmount battery, A/C eliminator kit, 3000 stall tci streetfighter, AOD with transgo kit, A+ servo, 300M hardened lockup shaft, kevlar bands and 28,000 gvw trans cooler, 3 core radiator, 300 lbs stripped with a full interior

12-27-2002, 12:19 AM	#3
Fox Body Mustang Maniac Join Date: Sep 2000 Location: GA, U.S.A Posts: 2,266	concerning where the heat comes out, lift the hood and check to see if the small, hard plastic, black vacuum line by the firewall, on the passenger side, is apart. It should be over where the hoses go to the heater core, but right up against the firewall. It is possible that that line has come loose. Reconnect and this will give air to vents instead of just floor and defrost. Concerning the no heat, all I can think of is that if your heater core is good, you need to check and see if that when you set the heater from cold to hot, that it is actually doing something. It will be hard to see/find, but see if you can somehow see if when you change the setting from cold to hot, there should be a wire (almost coathanger wire thick) that draws a door closed. That is what sets it to heat. If that wire is somehow disconnected, then it is not pulling the "door" or "flap" shut. That is definately one reason that could be the problem. That wire is also held to the flap with a plastic piece and if that piece has broken, then the wire isn't connected to the flap and if it has been previously set to cold, then you won't be able to draw it back and, therefore, no heat. That is what is actually wrong with my car. So I just leave it on hot setting. I know I may be being kinda vague, but that's really all I can think of now (This is if the core is fine). Hope it helps a little. __________________ 351W-powered 1979 Ford Mustang Ghia notchback '79 Video @ Idle Stock 5.8L under 4" cowl 'glass hood, C4 w/ Transgo shift kit, Holley 750 cfm, Edelbrock Performer RPM intake; Fluidyne Al radiator, Flexalite 175 electric fan, 1 5/8" MAC shorty headers, FRPP Al driveshaft; S&W 6-point cage; 2.5" Off road H-pipe, 2-chamber Flowmasters, 8.8" Rear w/ 3.55s; Weld wheels (15x6;15x8), Front: 225/60/15, Rear: 275/50/15 Nitto NT 555R Drag Radials; 14 x 4” K&N X-stream air filter. '92 GT (5-speed) Small In Car Video Stock 5.0L, 2-chamber Flowmasters, MAC CAI, Tri-Ax, Al pedals... "Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body

12-27-2002, 12:30 AM	#4
Chris_H Registered Member Join Date: Oct 1999 Location: New Mexico Posts: 488	I can't believe that I didn't even think to check that door for the air. I had that problem last year, but its because the gears in the control knob were worn out. i will also have to check that vacuum line tomorrow. I didn't even know there was one for this. Thanks a lot. I'll let you know how it goes. Chris __________________ 1987 LX, Best times: 13.47 @ 102.49, 1.80 60ft 6900' DA

12-27-2002, 07:09 PM	#6
Chris_H Registered Member Join Date: Oct 1999 Location: New Mexico Posts: 488	No such luck. Got up under the dash today when I got home from work. All the lines are hooked up, the temperature "wire" is opening the door like it should, and all the vacuum lines under the hood are good. I even have the boost gauge line spliced in with the A/C line, and the boost gauge works. Should that be spliced into the A/C line? I just got to thinking if thats a good idea or not.... Any other suggestions? If not I have about had it. I have a commuter car and I will rip this whole A/C system out before I lose my mind with it. I'll just deal with the 110* in the summer and the ice on the windows in the winter when I do drive it. Chris __________________ 1987 LX, Best times: 13.47 @ 102.49, 1.80 60ft 6900' DA

12-27-2002, 01:44 AM	#5
93blkGTfun Registered Member Join Date: Apr 2002 Location: Evansville, IN Posts: 98	I had the exact thing happen in my stang. The plastic vacuum line under the hood was broken. It was the one that is connected to the one that says A/C on the tee on the driver's side of the firewall.

12-30-2002, 07:14 PM	#7
84LX89GT Mustangs Join Date: Jul 2000 Posts: 1,938	Defrost is a default setting for the heater system for when there is a vacuum problem. Did you check for vacuum from the lines at the vacuum motors (the drum things). There should be a fresh air/recirculate door for when max A/C is off/on, a condensor/heater core door for heat selection, a defrost door and a vent/floor door. Because of the fact that you can't change Heat OR the location that sounds like to me you don't really have a vacuum distribution problem, but rather a supply problem. Check at the heater control unit to see if vacuum is getting to the control unit (the thing with knobs you turn), if not trace that to the vacuum tree on the firewall. One thing it also may be is that there is a vacuum reservoir for low vacuum conditions (such as wide open throttle, heavy throttle conditions). If you have a large leak for the reservoir vacuum circuit it may cancel vacuum to the door supply system. First i'd just check and see if vacuum is actually getting to the control unit, if not then check at the tree where the line is, if so i'd trace along that vacuum line and see if there are any splices/alternate paths it may follow. I forget off the top of my head where the reservoir is spliced into, but if you need the info i can look it up. Good luck, keep us posted. __________________ 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) Last edited by 84LX89GT; 12-31-2002 at 02:44 AM..

01-01-2003, 10:56 PM	#8
Chris_H Registered Member Join Date: Oct 1999 Location: New Mexico Posts: 488	Well I have checked the lines at the tree on thr drivers side, and the lines going into the firewall on the passenger side. I don;t see anything wrong with the vacuum lines. This is getting to be a pain in the butt, and not even worth my time anymore. To me, the next step is to rip everything out and lose the weight. After all, who needs a/c when it gets to be over a 100* during the summer. Chris __________________ 1987 LX, Best times: 13.47 @ 102.49, 1.80 60ft 6900' DA

01-01-2003, 11:40 PM	#10
Chris_H Registered Member Join Date: Oct 1999 Location: New Mexico Posts: 488	Ok, what is the best way to check for a vacuum leak? Will I feel it, hear it, something I can spray around it to see if it's leaking? Sorry, just don't know the best way to find a leak. Chris

01-01-2003, 11:55 PM	#11
HotRoddin cranky old man Join Date: Sep 2001 Location: Longview Texas Posts: 683	You should be able to feel it .. pull the line off and hold your finger over it, or put it to the edge of your lip (more sensitive) then actuate the control ... you should feel the suction.

01-02-2003, 05:32 AM	#12
84LX89GT Mustangs Join Date: Jul 2000 Posts: 1,938	HotRoddin is correct you will be able to feel it with your finger on the vacuum line and you'll also probably be able to hear it as well with the line disconnected, also make sure that the line your checking at has the door control knob in the correct setting (if you're not sure just tinker around with the settings until (if) you set something). Unfortunately this is one of those things that may not have an easy answer except for arduous step by step diagnosis. __________________ 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)

01-02-2003, 10:37 PM	#13
Chris_H Registered Member Join Date: Oct 1999 Location: New Mexico Posts: 488	Ok scratch everything that was said above. just found out today that the heater core is leaking for sure. Started to smell antifreeze, and sure enough its coming out the little drain hole. I have changed it 2x already, not in the mood to make it 3rd times the charm category. Thanks for the help, sorry to give up on it, but I am just not in the mood for it. The car is slowly becoming more of a weekend driver anyway. Take care. Chris

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