A/C VARIABLE ORIFICE VALVE ???

Greg Pettit

Full Access Member
Joined
Nov 9, 2007
Posts
91
Reaction score
0
Location
Denton, TX
I can't stand this any longer...... a long ass A/C thread and not one person has asked about high and low pressures, or what kind of refrigerant is being used.

So.

What refrigerant are you using, how much did you put in, what are your pressures, and what is the ambient temp?

Greg
 

MIDNIGHT RIDER

Full Access Member
Joined
Sep 29, 2005
Posts
4,636
Reaction score
38
This is in the first sentence of the first post in this thread.

factory air converted to R134a,



At idle, MAX-A/C, on two seperate gauges, I have 44-whatever on the gauge.


That is about what it always had before the hose replacement episode.


As stated, the low side reads 44-PSI (or whatever the numbers denote).

As the high side still has the original R-12 fitting, I haven't the necessary adapter to take a high side reading.What do I need to remedy this ??


I can't stand this any longer...... a long ass A/C thread and not one person has asked about high and low pressures, or what kind of refrigerant is being used.

So.

What refrigerant are you using, how much did you put in, what are your pressures, and what is the ambient temp?

Greg



The air-box housing has recently been completely removed and the evaporator cleaned through and through, along with the fan-motor being pulled and all leaves and **** cleaned out of there as well.


If by "ambient temp", you mean the outside temperature, it has been in the low- to mid-90s every day for the last couple weeks.


I added four 12-oz cans of R134a after pulling the vacuum.



I hadn't thought of feeling the temperature differences above and below the orifice valve.


My accumulator and the top of the compressor bead up with sweat.


As already stated, prior to my leaky hose, with the plain old orifice-valve, I regularly had mid-40 temperatures at the vents; now, I am seeing low-50s at the vent.


Thanks.
 

Greg Pettit

Full Access Member
Joined
Nov 9, 2007
Posts
91
Reaction score
0
Location
Denton, TX
High side pressures are very important. There are commonly available adapters that will work with the smaller Ford R12 fitting and convert it to an R-134 fitting.

R134 high side pressures are much higher than for R12. As a general rule, you want to see no more than 3x ambient temp for high side pressures at 1500 RPM with the blower on high and outside air selected. For example, if it is 90 degrees out, you'd look for a max of 270 psi on the high side.

Also, R134 conversions usually take only about 80% of the charge listed for R12. Overcharging can and will cause high vent temps and blown blow off valves at the compressor.

If the fan clutch is weak, you won't be getting the airflow thru the condenser that is required....especialy with R134. Even at road speeds, the fan needs to be puling to get air thru the condenser.

Low side pressures should get down into the 20's for best cooling. The R134 a/c cycling switches are generally set to shut the compressor off at around 25 psi. If 44 psi is as low as your low side will go, you are either overcharged or the compressor is weak, or the fan isn't pulling air thru the condenser.

All this assumes at least one full hour of vacuum applied to the system and NO air contamination. This includes any air in the a/c gauge lines. They must be bled prior to connecting to the system, or a big gulp of air goes right in with the refrigerant.

Greg
 

MIDNIGHT RIDER

Full Access Member
Joined
Sep 29, 2005
Posts
4,636
Reaction score
38
If the fan clutch is weak, you won't be getting the airflow thru the condenser that is required....especialy with R134. Even at road speeds, the fan needs to be puling to get air thru the condenser.


The fan is DIRECT-DRIVE with the clutch being "pinned".


All this assumes at least one full hour of vacuum applied to the system and NO air contamination. This includes any air in the a/c gauge lines. They must be bled prior to connecting to the system, or a big gulp of air goes right in with the refrigerant.

Greg

I left the vacuum-pump on for around an hour, then let it hold a vacuum for about half an hour.


That bit about bleeding off the air trapped within the hoses is good information.


I will get the high-side R134a adapter fitting and get some high-side pressure readings.

Thanks.
 

RLDSL

Diesel fuel abuser
Joined
Dec 14, 2005
Posts
7,701
Reaction score
20
Location
Arkansas
An hour on the vac pump probably was a bit shy for getting all the moisture out unless you got ahold of one of their real high end pumps.

44 on the low side seems a bit high if you have a pinned fan clutch unless it was hotter than hell out, or you were overcharged, and I have a feeling it may be the latter. R134a systems will suck big time with an overcharge
 

MIDNIGHT RIDER

Full Access Member
Joined
Sep 29, 2005
Posts
4,636
Reaction score
38
An hour on the vac pump probably was a bit shy for getting all the moisture out unless you got ahold of one of their real high end pumps.

The pump I used was a ??Robinaire?? MasterVac or VacMaster, great big heavy professional outfit that a retired auto-A/C mechanic allowed me to use in sworn secrecy.

He said it would pull more in fifteen minutes than most would pull in a day.



44 on the low side seems a bit high if you have a pinned fan clutch unless it was hotter than hell out, or you were overcharged, and I have a feeling it may be the latter. R134a systems will suck big time with an overcharge



I added four 12-oz cans of R134a to my evacuated system; how many are normally used in a standard factory 1985 Ford diesel ??


Should I have a portion of the refrigerant drawn off to a lower level ??

At five-bucks a can, poor as I am, I can still afford to experiment a little.

Thanks.
 

RLDSL

Diesel fuel abuser
Joined
Dec 14, 2005
Posts
7,701
Reaction score
20
Location
Arkansas
The pump I used was a ??Robinaire?? MasterVac or VacMaster, great big heavy professional outfit that a retired auto-A/C mechanic allowed me to use in sworn secrecy.

He said it would pull more in fifteen minutes than most would pull in a day.







I added four 12-oz cans of R134a to my evacuated system; how many are normally used in a standard factory 1985 Ford diesel ??



Should I have a portion of the refrigerant drawn off to a lower level ??

At five-bucks a can, poor as I am, I can still afford to experiment a little.

Thanks.

It sounds like you have a pump similar to mine :D no worries

48 oz would have been right on the nose..for R12, that's what the book says, but my handy dandy AC adviser program converts that to 38.4 oz for r134a so you do have an overcharge situation which will make your ac performance stink
 
Top