A/C Goes from cold to hot intermittently
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A/C Goes from cold to hot intermittently
My daughter's truck is a 98 F-150 Super Flare Side with a 5.4L V8. She complained about the AC not working so I checked it out. Pressure was fiine and compressor cycled. But the air was hot. What I figured was the blend door was stuck. But occasionally you can turn off the AC and turn it back on and it will be cold.
I finally took it to the shop to get fixed while I was out of town. The guy told me that the blend door hinge point was broken and the entire housing needed to be replaced at the cost of $1000 or more. I told him to make the door stay open and button up the dash. This didn't fix the problem unless he ignored my request. So this weekend I will get into it and fix it.
What do you think? Blend Door not operating? Vaccuum temp selector? The truck's possessed? And do I really have to remove the entire dash to get to the blend door?
Thanks for the input.
I finally took it to the shop to get fixed while I was out of town. The guy told me that the blend door hinge point was broken and the entire housing needed to be replaced at the cost of $1000 or more. I told him to make the door stay open and button up the dash. This didn't fix the problem unless he ignored my request. So this weekend I will get into it and fix it.
What do you think? Blend Door not operating? Vaccuum temp selector? The truck's possessed? And do I really have to remove the entire dash to get to the blend door?
Thanks for the input.
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anytime you get air out of the ducts that is warmer than return air than you are getting a heat exchange from the heater core. most likely a blend door like you orignaly thought. here is some food for thought. if you can turn off your a/c for a minute, and it gets cold agian for a set amount of time, and then gets warm. a couple things could be happening. you could have a failed pressure clycling switch not clycling the clutch properly allowing the evap to freeze over. Or you possibly have moisture in the refridgerant and its freezing the oriface, not allowing reefer to bleed into the evap. has this system been servised recently? Do these symtoms change with the ambient temp? Looking forward to your reply
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Thanks for you reply. No the system hass not been serviced. I did hook up a can of freon with a guage the first time she discovered the problem, but it didn't need much. Very little in fact. I watched the system running and the clutch cycles in what I consider a normal amount. However, when the air is shut off and turned back on immediately it sometimes comes back on cold. BTW, how often should the clutch drop out? I have just started the truck and am running it now. I watched the clutch closely and it doesn't cycle as often as I think it should. Maybe I'm not used to a perfectly working system? Any way, it's been running quite a while now and it still blows cold. According to my daughter you just turn it off and right back on and it starts getting cold again.
Last edited by ScottInTexas; May 18, 2007 at 04:55 PM. Reason: BTW
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From: Lorain County, Ohio
If the pivot point is broken there is no way to block the blend door in any position, so he probably didn't do that. The end of the blend door shaft that engages the Blend Door Actuator breaks off and the door is free to move around. Because of the airflow, it goes from one extreme to the other. This is a pretty common problem, and yes you have to pull the instrument panel. (Yea, it stinks). You then have to split the HVAC case to replace the blend door. If you are comfortable with repairs and have the shop manual it's not a particularly hard job, it's just time consuming. You really need the manual if you've never done it before.
The compressor cycling rate will vary with ambient temperature, engine speed, vehicle speed, humidity, etc. At idle on a hot day it will not cycle at all. At 60 degrees at 1500 RPM, it will cycle off fairly quickly. There's no real spec for it but approxomate times are given in the manual, FWIW.
The compressor cycling rate will vary with ambient temperature, engine speed, vehicle speed, humidity, etc. At idle on a hot day it will not cycle at all. At 60 degrees at 1500 RPM, it will cycle off fairly quickly. There's no real spec for it but approxomate times are given in the manual, FWIW.
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More info on old problem. This adds a new dimension to the problem discussed here. If you excelerate hard from a light for instance, the A/C blend door shifts. You can hear it. And you have hot air. If you turn the AC off and wait a few seconds you can turn it back on and you get very cold air. Sometimes it doesn't come back to cold for a few minutes and you have to turn it on to see then turn it off if it is hot air. My wife said she heard it change when she hit a bump.
If the temp control switch is electrical then I can see a bump shaking a bad connection. But I can't see it repairing itself by shutting of the system. It seems more likely that changing the temp would make things happen. If it is vacuum controlled then something is causing a vacuum change. Where would I look for that? My Haynes isn't very helpful with this sort of thing.
If the temp control switch is electrical then I can see a bump shaking a bad connection. But I can't see it repairing itself by shutting of the system. It seems more likely that changing the temp would make things happen. If it is vacuum controlled then something is causing a vacuum change. Where would I look for that? My Haynes isn't very helpful with this sort of thing.
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Fleet Mechanic
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From: Lorain County, Ohio
Originally Posted by ScottInTexas
More info on old problem. This adds a new dimension to the problem discussed here. If you excelerate hard from a light for instance, the A/C blend door shifts. You can hear it. And you have hot air. If you turn the AC off and wait a few seconds you can turn it back on and you get very cold air. Sometimes it doesn't come back to cold for a few minutes and you have to turn it on to see then turn it off if it is hot air. My wife said she heard it change when she hit a bump.
If the temp control switch is electrical then I can see a bump shaking a bad connection. But I can't see it repairing itself by shutting of the system. It seems more likely that changing the temp would make things happen. If it is vacuum controlled then something is causing a vacuum change. Where would I look for that? My Haynes isn't very helpful with this sort of thing.
If the temp control switch is electrical then I can see a bump shaking a bad connection. But I can't see it repairing itself by shutting of the system. It seems more likely that changing the temp would make things happen. If it is vacuum controlled then something is causing a vacuum change. Where would I look for that? My Haynes isn't very helpful with this sort of thing.
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OK. It has definetly been a while. But I'm going in. I have isolated the problem to the blend door just flopping around. If it goes to heat I can put it back in position by slamming the breaks real hard. Can't do it with others in the truck, but I did manage to verify it is the blend door. I have Haynes manual and tools. Is there anything special I should be aware of before I take out the instrument panel?
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From: Lorain County, Ohio
Don't count too much on that Haynes manual. It's practically worthless for this procedure. PM me and I'll send you a copy of the 1998 Ford Truck CD. You either need that or the factory paper manual if you've never done this before. It's not hard, there's just a lot of small details. Give yourself an entire weekend to get it done.
The reason the AC needs to be recovered is because the heater\AC box will be removed from the vehicle. The AC evaporator core is inside the box. You'll also have to drain the cooling system. You have to split open the box to replace the blend door. This is a great time to replace that 10 year old heater core too. Murphys Law says it will start leaking within 6 months if you don't.
The reason the AC needs to be recovered is because the heater\AC box will be removed from the vehicle. The AC evaporator core is inside the box. You'll also have to drain the cooling system. You have to split open the box to replace the blend door. This is a great time to replace that 10 year old heater core too. Murphys Law says it will start leaking within 6 months if you don't.
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