My A/C works for a while then all the sudden will go warm. No change in RPMs or noise accompanies the temperature change. I turn the control **** to "Off" for a few minutes, then back on and it starts blowing cold again. Then again, after 10 min or so goes warm.

What could be causing this?

 

What year is the truck? Do you have manual or electronic temp controls?

 

Sorry for the lack of information.

F-150 1998 Extended cab, Short box. 4.6 V8. The temp controls are manual. I have had to switch the ***** for the temperature and fan speed because the temp one got stripped out a little bit. The temp one is still stripped out some, but I wouldnt think that would make it go from coldto hot without touching it

 

Sometimes it goes warm after running 10 minutes, sometimes it will stay cold for a couple hours.

 

are you low on refigerant?

 

I dont know if I am or not. I need to check that. Would that cause it? I would think that if I was low on refrigerant it would just be a steady warm temperature. But then again Im no mechanic.

 

I've noticed that my AC starts giving the cold then warm cold then warm sign when its low. I would go to the auto parts store and buy a can of R134a that has a hose and quick connect already on it, it should be ~$15. They, the connections, are typically universal but just confirm before you buy. Directions are on the back of the can, but start your engine and set your AC to Max, temperature to its coldest, and the fan setting to its highest. Then pop your hood and connect the can to the AC connection closest to the firewall, I forget if it's the high or low pressure port the can will tell you. I would recommend at this point that you put on a pair of nice leather gloves or mechanic gloves because the can will get very cold very quickly. Depress the can's button, with it connected to the AC, and when the can stops filling the AC your full. This, at least to me, is a very slow and boring process but most of the time no longer than 10 minutes. When you are finished, you should notice results immediately and that the AC is blowing ice at you.

As to what causes your system to become low on refigerant, there are a couple of causes. In theory, it is a closed system and should never leak, but like everything else it can and will. I'd look at the lines, and more importantly the connections in the lines and use a AC detector kit (again readily available at the auto parts store) to find it. Then if that is the case, they have repair kits that seem to do a good job if you get to them when they are small. Another reason could be that over time and use refigerant will evaperate. Given a long enough time and evaperation rate, then you'll be low enough to affect the AC output.

Personally, I use about 2 cans on my 94 Sable per year so I know it has a leak. But $30 of AC refigerant a year is a small price to pay to have AC in the summer. My truck, an '06 4.2L, has never needed any AC service what so ever since I bought it.

 

I had the exact problem, the AC blowing cold, then warm , then cold. Drove me crazy. I thought I may have a bad blend door, the door that shuts air to the heater core or the AC. I replaced that door...not fun, found out it wasn't the problem. While in there, I think I did discover the problem. The blend door actuator worked fine when the ac/heat dial was on hot, the door closed to the heater core as designed but once I turned the blend **** to cold (blue) the door in the heater core would close off the heat as designed but would open and close at will. So, I am replacing the actuator. Part costs $49. Kind of a pain to get to but if interested I could tell u what to do. Good luck

 

To clarify my above post, the reason my ac was cold for 10 minutes then would blow warm and sometimes hot, then cold again is because the blend door was opening and closing thus allowing cold or warm air into the cabin depending on if it was open to the heater core or to the ac vents. There are only really 3 parts to this ac/heat system. The control ****, the blend door actuator (that mechanically opens or closes the blend door) and the blend door. Fords do have a history of broken blend doors, they are plastic and break at the base so that is why I thought that was my issue. Will get my actuator today and will post my results once I get it installed.

 

This might be my problem as well. I went and bought a can of refrigerant and went through the re-charge procedure. It seemed to work for a few days then started to do its cold-warm-cold thing again. So either I have a refrigerant leak or it is the blend door actuator you speak of.

I replaced the heater core a year or two ago in this truck and had to drop the steering column and pull the dash all the way out. Is this the same procedure to get to that blend door actuator? Or hopefully there is a way to get to it without doing all that. That was a huge project.

Looking forward to hearing about how your actuator replacement went and if it solved your problem.

 

Still waiting for the actuator to come in, Ford said it would be later today. As far as getting to the actuator, no you do not have to take the dash apart. you can do it from underneath. You do have to remove a few things to get to the actuator but nothing too difficult. Heater core installs are a nightmare! I will let u know how it goes when it comes in.

 

Sounds like my problem too.....06 F150, Manual temp controls. Will blow cold for a while then warm, then cool, sometimes down right hot air blows into the truck. Keep us posted!

 

Update. I think I have found the problem although I am still waiting for definitive proof. I picked up my new blend door actuator motor from Ford. When I installed it, I could visually see the blend door as I had cut a hole in the heater core plenum (another story). The new actuator was bad. The motor did not work at all, as I turned the heat/AC ****, the blend door did nothing. So, I re-installed my old actuator and turned the heat/AC ****. I found the blend door moved perfectly. Closing off the AC when the **** was turned to Heat, but when I moved the **** to cold that is where I found the problem. The door closed off the heater core as designed but then randomly would float open, allowing warm and depending on how far it floated open, sometimes hot air into the cab. It seems the distal ends of the actuator gears must be stripped, which prevents it from staying closed against the heater core. Ford said they will send me a new actuator Wednesday, so I will know for sure then but I feel confident that the actuator is the culprit. Again, it isn't a huge process for the fix, but getting to it is a pain in the butt. Cheap part however at $49. I promise to update either way and let u know if the actuator is the fix.

 

Glad to see they fixed this problem....my 08 is doing a simular hot cold routine.

 

i think all of you have overlooked something here. the a/c's on almost all modern vehicles have pressure safety switches that will cut the compress off if the pressures get too high or too low. I have experienced the hot cold thing too. On my truck I found that on warm days the high pressure switch was causing the compressor to remain off for minutes until the switch reset when the pressures decreased. Take note that the clutch fan does not always provide adequate airflow to keep the condenser cool and causes the high pressure switch to trip. You can check the switch by taking the connection loose from the pressure switch and checking for continuity while its not cooling. I removed to the switch entirely and strapped it off to the side. (not recommended). OR install some electric fans. try troyer