2002 A/C blows hot during acceleration. At idle, or when slowing down, it gets cold again.

[Ironhead]

My experience tells me it is vacuum related, but I have read a lot about dual coolant control valves and evaporator discharge sensors in this forum. Has anyone had similar symptoms?

 

[Gus Gutz]

When my dccv went bad all I had was cold air. I had no hot coolant running through the heater core. I tried all the usual stuff. I tapped in it with a long screwdriver but that didn't work. After replacing it, I got heat again.

 

[edward301]

Sounds like a little low on refrigerant, and at higher rpms low side pressure drops
below 22 psi so low pressure switch cuts compressor off.

 

[highwayghost]

I agree, to check the A/C charge first. If it persists, then check for a vacuum related issue with the blend door. Some vehicle blend doors are motor driven. I recently did a repair of the 4WD engagement on a F150 by adding a Motorcraft YG-360 vacuum check valve that helped with the loss of vacuum during acceleration. See the link.

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[The Flash]

99% of cars have the A/C defeat at full throttle. It's programed in the computer and it can't be changed.

 

[davea]

MANY cars have a compressors shutoff during acceleration, maximum horsepower to the wheels. Check this before you spend any money.

 

[Frankie the Fink]

The compressor cutout on WOT should NOT result in "hot" air blowing out the nozzles; maybe warm but not hot (like heater on hot). If that is occurring you have a problem. Yes, check the state of Freon charge. When my evaporator discharge temp sensor went out I had different symptoms. The A/C would freeze the crap out of passengers and the front panel controls had lost function...

 

[The Flash]

There are NO vacuum controls on the HVAC system in the cabin on my 2003 TB. I had it out of the car 2 months ago.

 

[highwayghost]

There are NO vacuum controls on the HVAC system in the cabin on my 2003 TB. I had it out of the car 2 months ago.

I have not had mine apart. Can you explain how it adjusts temperature, hot, cold, passenger, driver?

 

[edward301]

There are no vacuum controls, all electronic. For the AC sensors turn the AC compressor on and off to keep at
your set temperature.

 

[The Flash]

I have not had mine apart. Can you explain how it adjusts temperature, hot, cold, passenger, driver?

there are doors that are controlled by very small electric motors that move the doors so the airflow where the HVAC controls are set.


The dual automatic temperature control system maintains the selected vehicle interior temperature by heating and/or cooling the air.

• During A/C operation the system also reduces the relative humidity of the air.
• The driver may override the automatic mode of operation.

Principles of Operation

There are four main principles involved with the basic theory of operation:

• heat transfer
• latent heat of vaporization
• relative humidity
• effect of pressure on boiling or condensation

Heat Transfer

If two substances of different temperature are placed near each other, the heat in the warmer substance will transfer to the colder substance.

Latent Heat of Vaporization

When a liquid boils (converts to gas) it absorbs heat without raising the temperature of the resulting gas. When the gas condenses (converts back to a liquid), it gives off heat without lowering the temperature of the resulting liquid.

Relative Humidity

The amount of moisture (water vapor content) that the air can hold is directly related to the air temperature. The more heat there is in the air, the more moisture the air can hold. The lower the moisture content in the air, the morecomfortable you feel. Removing moisture from the air lowers its relative humidity and improves personal comfort.

Effects of Pressure on Boiling or Condensation

As the pressure is increased on a liquid, the temperature at which the liquid boils (converts to gas) also increases. Conversely, when the pressure on a liquid is reduced, its boiling point is also reduced. When in the gas state, an increase inpressure causes an increase in temperature, while a decrease in pressure will decrease the temperature of the gas.

The Refrigerant Cycle

During stabilized conditions (air conditioning system shutdown), the refrigerant pressures are equal throughout the system. When the A/C compressor is in operation it increases pressure on the refrigerant vapor, raising its temperature. Thehigh-pressure and high-temperature vapor is then released into the top of the A/C condenser core.

The A/C condenser, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at highpressure, exits from the bottom of the A/C condenser and enters the inlet side of the A/C receiver/drier. The receiver/drier is designed to remove moisture from the refrigerant.

The outlet of the receiver/drier is connected to the thermostatic expansion valve (TXV). The TXV provides the orifice which is the restriction in the refrigerant system and separates the high and low pressure sides of the A/C system. As theliquid refrigerant passes across this restriction, its pressure and boiling point are reduced.

The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C evaporator, it absorbs heat from the airflow passing over the plate/fin sections of the A/C evaporator. This addition of heat causes therefrigerant to boil (convert to gas). The now cooler air can no longer support the same humidity level of the warmer air and this excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.

The refrigerant cycle is now repeated with the A/C compressor again increasing the pressure and temperature of the refrigerant.

A thermistor which monitors the temperature of the air that has passed through the evaporator core controls A/C clutch cycling. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze,the A/C clutch is disengaged by the vehicle powertrain control module (PCM).

The high-side line pressure is also monitored so that A/C compressor operation will be interrupted if the system pressure becomes too high or is determined to be too low (low charge condition).