A/C blows hot and cold

2001 Taurus SE, 3.0L flex-fuel engine. When I first turn on A/C, I get cold air. After a period of time (sometimes hours, sometimes minutes, sometimes seconds), no more A/C, just hot air. Sometimes stopping the unit for a while will restore A/C, sometimes it won't. Last time I checked the refrigerant charge, it was up to spec. It's been doing this for two years now. Nothing came up when I searched the forum for this problem. No one seems to have a clue. Any of you kind folk have one?

TIA,

KM

Does it feel like there's less air blowing out the vents if there's a problem? If so, the system may be freezing up. Try turning of MAX a/c off after the car has cooled if freezing is the problem. This let's outside air get to the evaporator, which warms it slightly.

No, no loss of air flow when the A/C blows hot. Just loss of cold air.

You might need to have your A/C system serviced. It is suppose to be done every two years or so. And it probably won't run you more than $40.

You could be have a blend door motor or blend control switch going out. Ever tried tapping on the switch when it blows hot?

There is a blend door actuator that is located under the dash just to the right of center. When it starts blowing hot, there is a lever you can access to move the door to see if cold air will return. If you can manually make the air go to cool, replace the blend door actuator. It is normally a white plastic square that yas wires going into it.

Got my head down under the dash. I can see the blend actuator door moving when I crank on the temperature control. I can't see any way of moving it manually, however, as it's totally encased in a plastic box with no external handle of any kind. But that it's moving in response to turning the temp control suggests it's not the problem. The problem persists, and we just went through the hottest weather we've had since late last summer. I get maybe 30, 40 minutes tops out the A/C before it gives out. Guess I'll have to have the mechanic check out the system.

When the A/C stops blowing cold, does the compressor clutch continue to cycle, or just stay disengaged?

If the compressor clutch stops cycling, one thing you could try (although for safety reasons it's not recommended) would be to short the refridgerant pressure switch. If the compressor clutch is working, this should force the clutch to engage and the air should get cool. If you were to try this and the compressor did not engage, I'd start to focus on a heat-related open circuit in the compressor clutch coil. If the clutch did engage I'd be checking the pressures again and suspect either an overcharge or a low charge.

-Rod

I've had a similar problem and it turned out to be the low pressure switch was bad. The A/C would blow cold and then hot. When it starts blowing hot you got to check under the hood and see if the compressor is engaged.

Like Shorod said, try jumping out the low pressure switch if the compressor is not engaging. To jump out the switch, remove the plug on the switch. The plug has 2 terminals, just connect the 2 terminals together with a short piece of wire. This will complete the switch circuit and the compressor should run.

I suppose I could root through my aftermarket shop manual and try to find these switches, but somebody spare me the bad photography, please, and tell me where to find these particular switches. Shorod, how would I know if the compressor clutch stopped cycling? For what should I be looking/listening?

If you look at the compressor pulley, the center is a magnetic clutch. So, when the A/C is not switched on the center of the pully does not turn. When the A/C is on the center will rotate the same as the belt pulley. Pretty simple once you you look at it. Have someone start the engine and then turn the A/C on while you watch the compressor. You will hear a click and the center will start to spin and hopefully cold air comes out.

Low pressure switch is mounted on the accumulator on the engine side of firewall. Round black thing with 2 pipes going to it. Low pressure switch is usually screwed into the top. If the switch is bad you should have it changed at a shop cause they will have to evacuate the system.

wilbur 996 has the right idea. But to add to his post, if the a/c works for a while then stops, look at the accumulator he describes to see if it is frosting up. If it is, you can replace the low pressure switch yourself. It screws into the accumulator and has a schraeder valve in it so you will only lose a very small amount of refrigerant. it should stop leaking almost immediately when you unscrew it.