A/C problems

[ludvball]

The A/C in my car will not blow cold air. My father is a mechanic and has been helping me with this, and is scratching his head. Here are the things we have done. Please excuse my termonology, as i am not a mechanic.

The system has been evacuted and recharged. It is showing good pressures 250/35 (I think). It is not leaking. The compressor is cycling on and off more often than it should, but we determined that that is the cycle switch, and are replacing it. When we bypassed the cycle switch, and the compressor ran non stop, still no cold air.

visually inspected the evaporator and it looks like there is nothing blocking it.

Visually checked the temperature door passed the evaporator, and it looks to be funtioning properly (full open and full closed).

All of the settings for floor/defrost/vent seem to function properly.

Fan is operating.

I think that is the jist of what we have done. It blows hot air, but no cold air.

Thanks for any input

Kevin
93' LX vert

I know you all are going to say what do you need A/C in a vert for. I normally feel the same. 95 degree days with high humidity changed my mind.

 

[BlackGT89]

Are the low pressure side hoses / lines of the A/C system getting cold ? After a few minutes of running you should see sweating and if it's really cooling well the lines might even frost over for a second or two before it cycles. Are you running an electric fan on the car and if so is it coming on with the A/C ? Put a big fan in front of the car and let it blow through the condensor and radiator and see if that helps (that is if you are doing a lot of this testing while it's sitting still).

 

[PuterAmI]

BlackGT89 asked the right question. Look for the two lines at the firewall that connect to the evaporator. The one line coming from the condenser should be cold. The line coming back out should be close to the same temperature. If not, you have a blockage.

You say that you determined that the switch was bad. How? If the low side pressure drops below the point that it is set for (factory R12 25PSI), it shuts the compressor off. The most common place for blockage is the liquid line that contains the orifice. This is the line coming from the condenser that should be cold.

 

[jrichker]

The under the hood part sounds good, I would look inside at the vacuum operated controls. An obstruction in the liquid line would likely raise the head pressure beyond the 250 PSI he is getting.

Possible failure of the diverter flap that controls how much hot air gets mixed with the cold air.

 

[ludvball]

Thanks for the information. I will have to check to see if the lines are getting cold.

As i said my father has been helping me with this, and he determined that the switch was bad. I believe that he determined it because it was cycling every few seconds, and the pressures didn't really have time to adjust. I never actually saw what the pressures were pryor to bypassing the cycle switch. When he bypasses the switch the pressures then adjusted to 250/35. If what Puter said is correct, and what i remember the lowsside pressure to be is correct, then i am not even getting low enough to cycle the system off. Is that correct?

 

[ludvball]

Jrichker, i did check the diverter flap. I didn't pull the entire box out to check it, but i pulled the resistor out of the box, which gave me a 1"X3" hole to look through. It appreared to be functioning well. I can't confirm that it was closing all the way. As far as it was moving, it should have made some change in the temperature.

Once again, thanks for all your input.

 

[PuterAmI]

250/35. If what Puter said is correct, and what i remember the lowsside pressure to be is correct, then i am not even getting low enough to cycle the system off. Is that correct?

Correct. Also, a common issue with the Fox is the wiring at the WOT relay. This is a small rectangular box forward of the passenger-side shock tower. What is strange is that the insulation of these wires will burn. You need to check this and repair if necesaary. If this is the case, it normally screws up the switch.

You can also adjust the switch. Once you take the connector out, look down into it and you will see a screw. Turning it CCW (CounterClockWise) will LOWER the PSI that it turns the compressor off at.

So...

1) Inspect the wiring at the WOT relay and repair as necessary.
2) Try adjusting the switch so that it shuts the system off at ~25PSI. It should also re-engage the system at ~40PSI.
3) If #2 fails, a new switch can be had from Ford for ~$25.

Good luck. It's gonna be 100 here today. So glad I spent a little money on A/C instead of jerking it out.

 

[ludvball]

Thanks Puter, i will try that tonight.