BearKiller

Wife's truck.

For the last several years, I add a can of R134a to the wife's truck at the beginning of summer and get vent temperatures of 32* or lower.

The last few weeks, her A/C had been showing evidence that it was possibly low on refrigerant, with vent temperatures not much lower than in-cab temperatures.

Today, I hooked the gauges up and it shows an equalized pressure of 78-PSI.

Contrary to what I expected, engine at idle, MAX A/C, Low-side is 135-PSI and High-side is 70-PSI.

In the cab was about 92* and dash temps about 82*; after idling like that for a few minutes, dash temps actually went up to 85* and the Low-side went up to 140-PSI.

On shut-down, it took quite a while before pressures began to equalize.

Due to it's past history, I am certain it needs at least one can of R134a.

What is the problem ??

Many thanks.

rrgrassi

Could be a plugged drier or failed expansion valve.

Have you ever added oil with the additional r134? (I hope you did) With a freon leak, oil leaks also

Did you ever use the Stop Leak stuff? (I hope you did not)

BearKiller

NEVER use the stop-leak stuff.

Well, mysteries never cease to plague me ....

I let the truck sit for an hour or so and tried again.

This time, Low-side was 4-PSI and High-side was 100.

Added two cans and got 22/190-PSI with 44* dash.

Added a THIRD can and got 16/200-PSI, 30* dash, and heavy frosting on the lines.

The only thing I can figure is that she drove home with the drastically under-charged A/C ON and thus got the pressures out of whack; after sitting for a while, things leveled back to normal.

Would it be a good idea to add one of those small oil-charge cans; PAG or Ester ???; or, what ??

It is blowing super-cold again, she is happy, and I didn't spend any un-necessary time or money.

If I hadn't checked it out again, after sitting a spell, I would have still been puzzled.

Many thanks.

maybe368

An oil charge would be a good idea, especially if you have never added one. It is impossible to know how much oil is in there without disassembling the whole system and flushing it out. If it is factory 134A it should say on a label under the hood which oil was used. If not, maybe in the owners manual. My new VW has pag, for what it's worth...Mark Edit: I see that the wife's truck was converted to 134A. A little checking shows that pag and ester can be mixed, so it would be preference if you don't know what was used...

rrgrassi

The bad thing about PAG is that if forms acids when exposed to air. It is possible that your system is now overcharged.

I found this very helpful...http://www.ackits.com/aacf/ptchart.cfm

fazmig

Good morning all i just joined this forum and i dont mean to hijack the thread but i am currently experiencing the same problem. I have a 1990 dodge w250 that will only blow cold at night and early morning. I just replaced the ac compressor, expansion valve, drier and condensor and flushed out the whole systen. Also serviced with pag oil and r12. I bypassed the ac compressor cycling switch with the same results. Thank you so much your input would be greatly appreciated.

maybe368

Welcome to the board! It would be beter to post this as a new thread, you would get better responses. Is the sight glass clear? Have you checked to see if the fan plenum box is full? Is there good air flow coming from the vents?...Mark

rrgrassi

PAG does not mix well with R12. The oil and the freon must mix together to lube the compressor. You need to use either mineral oil or ester oil.

Jim Lane

This could also be a sign of moisture in your system.

How long did you evaporate your system after you got down to 29*

Jim

fazmig

Im sorry, i meant to say it was ester oil, not pag oil. Agaib, early morning and at night it coools down to 40 degrees and during the day anywhere from 60 to 68 degrees.

Busboy

If it's cooling to 40deg it's cooling, I would check your recirc door and make sure it's closing, also check the rubber hood seal along the top of the firewall, if that's missing or off it allows hot engine compartment air into the HVAC intake. Is your condenser clean and nothing touching it?

fazmig

Thank you for the response, my condensor is new and not touching anything, i am not sure how to check for the recir door.

Busboy

Put it to MAX AC and you should hear the fan noise increase, if you look under the passenger side dash close to the kick panel you should be able to see a plastic mesh with a door on the other side, you should see it move. Don't forget to look at the hood seal it does make a difference.

fazmig

That door completely moves to the closed position when i cycle it to max a/c. What hood seal are u referring to? Thank you.

rrgrassi

Did you pull vacuum on your system? It's the vacuum that boils out any moisture.