A/C works half the time

[dllights33]

I have a 95 Grand cherokee limited.It is a 4.0 with about 160k on it. At first when you put the climate control on the temp you want and turn the knob to auto it would work fine for a while then all of a sudden when it thought it was cool enough in the jeep it would turn on the heat full blast instead of slowing down the fan. So to get around that we would leave it on HI and the temp on Lo. That worked good for a season, now it does the same thing. It works good for a while then out comes the heat. Before it all started i noticed that before the A/C would come on it said ER instead of the temp I had it set on. I have changed the control head and the resistor that is next to the blower motor. Any suggestions would help.

[Bob D.]

Did you try to retrieve error messages for the HVAC system?
Do a search for BLEND DOOR.

[dllights33]

How would i go about finding a error message for the HVAC?

[dksob81]

turn the key to the ON position, PRESS and HOLD the A/C and RECIRC buttons, then turn the temp dial one click clockwise. "00" should be displayed on the HVAC controls, now push the A/C button. the stickman will appear indicating you have entered the fault codes test, the values displayed in the test selector will range from "00" to "64". The fault codes will appear and repeat if there are more then one. Record all fault codes and post them here, myself or someone else will let you know what they mean.

If code(s) "25" or "29" appear the ATC Module will need to be replaced before any further testing can be done.

[dllights33]

I did the test and the winning numbers are as follows....40, 43, 46, 52, and 23

[dksob81]

23 - Door travel range to small, Blend air door actuator drive circuit.
40 - feedback was too high, Blower/fan feedback circuit.
43 - Circuit was shorted, solar sensor input circuit.
46 - Circuit was shorted, Blend air door feedback circuit.
52 - Door was not responding, Blend air door actuator drive circuit.

It seems like your problem is due to a broken blend air door. and bad Solar sensor - or just a short in the wires, I would check for bad wires first. The solar sensor is located in the WINDSHIELD DEFROST GRILL, this sensor senses solar (sunlight) intensity and adjust the air temp. at the vents depending on the intensity of the sunlight.

[dllights33]

I changed the blend air door actuator last year. Probally before all this started happening. It went bad becouse the condinsation was leaking in the floor board and soaked up the carpet and padding and rusted up the actuator. When I changed it the door seemed fine. It opened all the way and shut tight. Mabey my new actuator is not working right?? I don't know. I am assuming I have to pull the dash out to change the blend air door and the solar sensor? BTW thanks for the help so far.

[dksob81]

Yes, you will have to pull the dash out to replace the blend air door.

The solar sensor is on top of the dash, center next to the glass. You will have to pull the defrost grill off tothe repalce the solar sensor - no big deal there, maybe 10 minute job.

[dllights33]

Thanks for the help. I am going to change the solar sensor first and look for bad wires before I tackle pulling the dash out. I will let you know how things work out.

[dllights33]

I have ordered the solar sensor from the dealer but I went ahead and checked the codes one more time for good measure. I got to different codes the last time one was 20 and the other was 55. Can you tell me what they mean.

[dksob81]

20 - Door not responding. Blend air door actuator drive circuit.

55 - Door travel range was too small. Blend air door actuator drive circuit.