83 300sd ac problem
 

Rebuilt compressor installed over one year ago, new expansion valve installed. Connected all fittings, but never got around to recharging system or putting ac compressor belt on until last week.
Pulled a twenty minute vacuum with a commercial pump, charged system. Low side pressure holding at 45-50. Almost no reading on high side. Clutch engaging on compressor. Hot air only out of vents.
Any suggestions?

ha, did you recharge it with hot air?

The origin of hot air is no longer a mystery. Much to the dismay of many respected physicists, you have scientifically proven that hot air does indeed NOT rise, it falls below in worthless postings on websites. Thank you. Future generations of science majors will now need to pay exhorbitant fees for newly written textbooks.:rolleyes:

Hopefully any other posts will be not be a complete waste of my time.

I am wondering if there may be a vacuum control issue. The vacuum lines are very brittle with age. Could a vacuum leak elsewhere in the system cause the expansion valve to not perform correctly while not causing the engine to run in an obviously irregular manner?

I have the same question, but you can forget about the "hot" part.

Did you use a vacuum gauge when evacuating? Did you disconnect the pump and then connect the refrigerant can, drawing in air, when you went from evacuation to recharge?

I know for a fact that you didn't use a micron gauge, or there's no way that you would have stopped the evacuation process after a mere twenty minutes.

It could be a lot of things. Your vacuum lines could very well be your problem. If that's the case, the vacuum element that switches hot/cold air would not be getting any vacuum, or it's just stuck in the heat position. See if you have a vacuum leak or if that precise element (they're all pink) is just stuck and needs replacement.

There are some seriously smart AC people on this board , hopefully they have some solid answers based on science and mechanics.

From what I remember we pull vaccum to evacuate moisture... leaving it closed with out evacuating concerns me, unless you live in the desert where I do - the air is very dry here.

People talking about vacuum lines make me think they are talking about pods opening properly and cold air being blown in the cabin. In other words, sort of assuming that the expansion coild is producing cold air and you don;t get to have any.
But if that were true the large (low pressure) line of your AC system would be cold and sweating under the hood. And I think your large line may not be cold at all. Which means you are not compressing and expanding your freon as expected.

I hate asking , cause this makes people crazy here, but R12 or R134 ?
Don't matter to me. How much did you get in to the system ?
Pressure is important , but so is quantity of freon.

Personally 12 or 134, they both get cold.

I think you are okay. I have always let my systems sit under full vacuum for at least 12 hours before freon goes in, mostly to determine if it leaks.
I hope you got full vacuum (adjusted for altitude).

You sound touchy, overwhelmingly hostile, and unable to perceive the obvious joke. You wouldn't happen to be from, or at least living in, California?

And I don't think there has ever been a mystery of the origin of hot air. It comes from the hubris. Many people have known this for a long time.

None of your logic follows.

You are welcome.

what do you mean, no pressure on high side?
are your gauges reading properly? there's no way you have 50 on low side, and NOTHING on the high side. get a better reading, post answers to the questions posted, and lets figure out what's up.
and vacuum has nothing to do with the expansion valve.