99 f150 4.6

Just charged ac. Low pressure line very cold. Compressor cycling every 10-15 seconds. Box is cool/almost sweating under glove box. On Maxi- Cool::

Problem: Steady air blowing out vents, but not cold. Almost like the air is not passing thru the evaporator.

The maxi damper behind the glove box is fully open.

Fan works fine but power wires seem unusually hot to the touch

What is not opening/closing to let air pass through those chilled coils?

Any photo or diagram would be most helpful.

Many thanks!

 

That's too much cycling, it's likely still low on charge.

 

Need to hook up a set of gauges and see what the pressures are. Don't trust the gauge on the auto parts can and dont put any stop leak in the system. Most of the parts store recharge cans have stop leak.

 

Ok. Good advice. Thank-you. Fortunately, I didn't buy 134 with stop leak, but did rely on can gauge and stopped when in the appropriate color. Its certainly possible there is not enough freon in the system, but since low pressure line was cold to touch, I figured I ought to be feeling something inside.

SIDE NOTE: The internal damper (behind radio) that swings air to defrost or panel was removed due to dry rot off its turning rod.(It was actually lodging in there)
I figured this would only eliminate defrost as (exclusive), which if I then closed panel vents, should move air north.

As I understand the system, there is that vacuum damper , just mentioned, an electric damper motor that runs vertical, for heat....and the maxi damper that recirculates interior air. Did I miss any?

Thanks for your valued input....

 

The "flapper box" is vacuum controlled and only regulates which vents the air blows from, whether defrost, dash, or floor.

The temperature is regulated by the blend door via an electric motor.
All the air always passes across the cooling part, the blend door swings to open or close the air from passing the heating part.
What breaks is the axle or hinge on the blend DOOR itself.

Assuming your AC system is correctly charged and generally operating correctly otherwise, a broken blend door will often be evident in random drastic temperature swings that may or may not be induced by vehicle motion either over bumps or turning corners.

The original 2 piece blend door repair part that I remember is caller heater treater, with an awkward spelling. Look up their videos on YouTube for a really good explanation of how the blend door works, how to diagnose if it is bad, and how to repair it the quick and easy way.

 

This may be the best news all day. What Im hearing is, if I turn the **** to heat and I get strong heat, lets say at the floor, I can assume the blend door you speak of did move from the "cold" position to the "heated" position, which may be the best news all day. This might then tell me that I still dont have enough refrigerant in the system.

If the system was empty, and Im pretty sure was at or near empty, can there be an air-lock created when adding new refrigerant...? Is there a way to "burp" the refrigerant?

Again, many thanks!

 

Well the proper way to do it is to evacuate all the refrigerant (and air & moisture, etc.), hold a vacuum on the system for 30 minutes and then refill it with the CORRECT amount of refrigerant using a good quality set of gauges.
But if it has a slow leak and still works fine for most of the summer, what often happens is that refrigerant is fed in until it won't take any more and send it. Then forget about it until it stops cooling satisfactorily and the process repeats.

 

when you connect the gauge set or a new R134 can with a cheap gauge on the hose, you SHOULD read a pressure BEFORE you start to fill... If the system is properly charge, you might see 90- 100 pis BEFORE you start the motor and turn on the AC... The LOW and HI sides will balance out when the system is OFF... If you have 40-50 psi, then the system is about half full.. if you have ZERO pressure, then you have a leak.. Must be fixed, then pull a vacuum and hold to test as mentioned above.

If you add a can of R134, you should see the pressure go up to about 45 psi, then compressor engages and sucks it down to about 25 psi, compressor shuts off, pressure back up to 45, the compressor engages again... you might have the compressor ON for 30 seconds, and off for 10 seconds... If it cycles every 10- 15 seconds, your way low on R134.............. and for a good test, you should have the motor at 2000 RPM to check the cycling and pressure as that's what the motor speed will be when running down the road........ testing at 600 RPM may not give good results.