Need A/C help

[MYBAD79]

long story.... AC .... '93 Mustang (2.3L 140ci 4cyl):

Converted the R12 system to 134a a few months ago, everything worked fine. Two weeks ago I noticed the AC did not blow cold air... compressor belt slipped a few times... ok, I thought it was a result of the R12-134a conversion ... wouldn't be the first conversion going bad...

Checked the pressure on the low side with cheap gauge first: high pressure all the way in the red area.... verified with gauge set: 60psi

Suspected a blocked orifice tube, maybe plugged with compressor debris... ok, at that time I thought that sometimes shit just happens and maybe I did not get all the R12 and the mineral oil out before refilling with R134a and PAG oil...

I bought a new (rebuilt) compressor, dryer with hose assembly and orifice tube with hose assembly. I flushed a gallon of cleaner and shop air thru the evaporator and condenser to make sure it's clean.

I installed the new parts, got a vacuum pump and gauges from AutoZone (loaner tool) and tried to charge the system today.

Before I connected the hoses to the compressor I filled the compressor with 8oz PAG46 oil (per instructions from the compressor rebuilder). Then I evacuated the system with the vacuum pump... no leaks ...

I managed to get 1/2 a bottle of 134a in the sytem then the pressure on the low side was up to 80psi....wtf ???

I'm beginning to think that the parts I replaced were not bad to begin with... good thing I got very good deals on the parts... anyways... now I have a clean condenser and a clean evaporator, new hoses, new orifice tube, new dryer and a new compressor.... too bad I still don't have a working system...

What would cause the pressure on the low side to be so high ?? I can't even get enough 134a into the system, right now it's barely half a can, maybe 6oz....

 

[MYBAD79]

I tried again (and failed) today:

I connected the vacuum pump and evacuated the system for about 40 minutes, turned off the pump, waited, confirmed no leak... ran the pump for another 10 minutes and then connected a can of 134a and let the vacuum suck the refrigerant into the system.
I started the engine and turned the AC to "max" - there was enough refrigerant in the system so I did not have to jumper the switch to get the clutch to engage.
Pressure on the high side went up to 150, pressure on low side went up to 60. At that time I had almost one can of 134a in the system, not enough to get any cool air... but too high pressure to add any more refrigerant....

 

[mrvette]

Because of the higher hi side pressures, I never bother with reading them, they are all over the map due to airflow and outdoor temps/humidity even....

I just look for 20f drop over the coil from ambient open doors/windows down recirculating air on high speed....in other words, no engine heat being sucked in, just the ambient from outside over the evap coils....

I typically find a MAX of two cans of 134 about does it....if not enough cooling add more, but not over 70-80% of the 12 fill cap.....

and ditch that damn PAG oil, I read over the years that PAG is bad news, to go ESTER oils, as them being more compatible with the R12 oils....

also, 150 lbs is a really LO high side pressure, I have read 300+ many times, and everything fine....

LO side shoud be about 25? lbs or so, running fast idle ~2000 rpm's....

that's about all I have done for years, other than the obvious repairs...

BTW, on conversions, somehow, one way or another, I loose a can/year of 134 at best....not a huge enough loss to worry over....

 

[MYBAD79]

problem is the high pressure on the low side. I had it up to 90 on the low side and 200 on the high side... got afraid it blows the refrigerant can in my hand....it should stay at around 30-40 and take refrigerant. difficult to add refrigerant against that high pressure....

funny thing is that the pressure on the low side was high BEFORE the parts were replaced - obviously I have not replaced the right part yet....

 

[mrvette]

NINETY on the LO side, with compressor running?? U sure??

that's more like a non running system, static load....

somehow there is a blocked line between your test hose/fitting and the comp inlet...it's not really sucking...

weird man.....dunno what to say...:surrender:

 

[010752]

With all the parts you replaced sounds like you have
Most likely,
a restriction in the system
or a bad compressor (valves)

A lot of times compressors come precharged with oil so adding the system amount can double it. Rule of thumb is 2 oz for every major part.
The right viscosity Pag is correct, most manufacturers will void the waranty if ester is used.
When adding oil try to add it in different places and always turn the compressor shaft by hand at least a dozen times so as not to slug it and blow the internal valves.

Take the system apart and blow the highest air pressure you can thru all the parts separately, especially the evap and condenser. Oil and other crap tend to settle in the bottom and is hard to get out. Flush forward and backwards several times. On rare occasions, an old oriface tube could blow thru and plug. It's best to take the parts out of the car if possible to flush.

If you used a air operated vacuum pump or not run a good one long enough, moisture can still be in the system. On my stuff, I always run it overnite, after testing for no leaks (at least 1 hour after pumping down). A cheap pump doesn't cut it. You have to get 29".
Make sure you precharge the charging hose.
You should have a static pressure on both sides of around 90psi.
Best way is to start off with 75% of the r12 capacity and adjust from there.

To test, engine at 1500 min, run water over the condenser with all fans on high to get best pressures after 10 minutes of stabilizing.

 

[MYBAD79]

I'll try cooling the condenser tomorrow...

(added comments in 'blue'):

With all the parts you replaced sounds like you have
Most likely,
a restriction in the system
or a bad compressor (valves)
Possible but unlikely in my opinion. I blew cleaner and air thru the only two parts that i did not replace: the evaporator and the condenser. Seemed to have pretty good flow. I did not verify the old orifice tube was still in the line where it belongs... it's already at the dump...
Doubtful that both compressors are bad. the new compressor (rebuilt) seems to work fine: got pressure up to 200 on the high side
A lot of times compressors come precharged with oil so adding the system amount can double it. Rule of thumb is 2 oz for every major part.
The right viscosity Pag is correct, most manufacturers will void the waranty if ester is used.
I dumped the oil that was in the compressor and refilled 8oz PAG46 into the compressor, did that after the compressor was installed. I did turn it b hand a few times.
When adding oil try to add it in different places and always turn the compressor shaft by hand at least a dozen times so as not to slug it and blow the internal valves.

Take the system apart and blow the highest air pressure you can thru all the parts separately, especially the evap and condenser. Oil and other crap tend to settle in the bottom and is hard to get out. Flush forward and backwards several times. On rare occasions, an old oriface tube could blow thru and plug. It's best to take the parts out of the car if possible to flush.

If you used a air operated vacuum pump or not run a good one long enough, moisture can still be in the system. On my stuff, I always run it overnite, after testing for no leaks (at least 1 hour after pumping down). A cheap pump doesn't cut it. You have to get 29".
Make sure you precharge the charging hose.
You should have a static pressure on both sides of around 90psi.
Best way is to start off with 75% of the r12 capacity and adjust from there.

To test, engine at 1500 min, run water over the condenser with all fans on high to get best pressures after 10 minutes of stabilizing.

 

[MYBAD79]

I have not replaced the pressure switch on top of the dryer yet.... what are the symptoms when that switch doesn't work??

 

[010752]

I'll try cooling the condenser tomorrow...

(added comments in 'blue'):

With all the parts you replaced sounds like you have
Most likely,
a restriction in the system
or a bad compressor (valves)
Possible but unlikely in my opinion. I blew cleaner and air thru the only two parts that i did not replace: the evaporator and the condenser. Seemed to have pretty good flow. I did not verify the old orifice tube was still in the line where it belongs... it's already at the dump...
Doubtful that both compressors are bad. the new compressor (rebuilt) seems to work fine: got pressure up to 200 on the high side
A lot of times compressors come precharged with oil so adding the system amount can double it. Rule of thumb is 2 oz for every major part.
The right viscosity Pag is correct, most manufacturers will void the waranty if ester is used.
I dumped the oil that was in the compressor and refilled 8oz PAG46 into the compressor, did that after the compressor was installed. I did turn it b hand a few times.
When adding oil try to add it in different places and always turn the compressor shaft by hand at least a dozen times so as not to slug it and blow the internal valves.

Take the system apart and blow the highest air pressure you can thru all the parts separately, especially the evap and condenser. Oil and other crap tend to settle in the bottom and is hard to get out. Flush forward and backwards several times. On rare occasions, an old oriface tube could blow thru and plug. It's best to take the parts out of the car if possible to flush.

If you used a air operated vacuum pump or not run a good one long enough, moisture can still be in the system. On my stuff, I always run it overnite, after testing for no leaks (at least 1 hour after pumping down). A cheap pump doesn't cut it. You have to get 29".
Make sure you precharge the charging hose.
You should have a static pressure on both sides of around 90psi.
Best way is to start off with 75% of the r12 capacity and adjust from there.

To test, engine at 1500 min, run water over the condenser with all fans on high to get best pressures after 10 minutes of stabilizing.

Depending on the ambient temps, in a well functioning 134 system, with a low side of 75psi a compressor can get your high side up to 375 - 400 psi. Won't last forever, but it will do it.
Yours was 90 and 200?

You can never get all the oil out unless you disassemble the compressor.

If the compressor runs, then the high or low or combo pressure switch is working well.

 

[MYBAD79]

I had the low side up to 90 when I forced 134a in the system.... used one of those refill kit hoses with gauge.... it was all the way in the red zone.... verified with the gauge set and it was 85....

You can never get all the oil out unless you disassemble the compressor.

I emailed those guys I bought the compressor from and I was told they only put 2oz of "test oil" in the compressor. I turned the compressor upside down and turned it by hand, got about 2oz of oil out of it....I was told that a small amount of that oil is fine with 134a and the pag oil....
If the compressor runs, then the high or low or combo pressure switch is working well.
good... so I can rule out the switches....

to be continued.....

 

[MYBAD79]

fixed it.... problem was insufficient airflow across the condenser. I hot wired the radiator fan motor and now it's blowing ice cold air... colder than ever before

Now I have to find out why the darn fan is not coming on :bomb:

 

[mrvette]

fixed it.... problem was insufficient airflow across the condenser. I hot wired the radiator fan motor and now it's blowing ice cold air... colder than ever before

Now I have to find out why the darn fan is not coming on :bomb:

Relay didn't close????:surrender::smash::clap:

 

[ToddG]

fixed it.... problem was insufficient airflow across the condenser. I hot wired the radiator fan motor and now it's blowing ice cold air... colder than ever before

Now I have to find out why the darn fan is not coming on :bomb:

Relay didn't close????:surrender::smash::clap:

Fan temp sensor on this model is located in the radiator correct..?
c-ya
ToddG

 

[mrvette]

fixed it.... problem was insufficient airflow across the condenser. I hot wired the radiator fan motor and now it's blowing ice cold air... colder than ever before

Now I have to find out why the darn fan is not coming on :bomb:

Relay didn't close????:surrender::smash::clap:

Fan temp sensor on this model is located in the radiator correct..?
c-ya
ToddG

Nothing to do with any TEMP, just as the compressor is on, the rad/cond fans have to be ON also...full bore....with good suction through, no bypass leaks, and air blockages...like junk in the airflow...

 

[010752]

Great, that was an easy fix

Some on these forums incorrectly recommend that when installing alum rads and elec fans that it isn't necessary to have the fans running for a/c.
Your problem shows this isn't true.

Even with an engine clutch fan, I add a pusher just for the a/c. The more flow the better for a/c, forget the engine cooling.

 

[mrvette]

Great, that was an easy fix

Some on these forums incorrectly recommend that when installing alum rads and elec fans that it isn't necessary to have the fans running for a/c.
Your problem shows this isn't true.

Even with an engine clutch fan, I add a pusher just for the a/c. The more flow the better for a/c, forget the engine cooling.

Since he is a sponsor, and I didn't want to get banned, and knowing enough of a/c work that his reply stated above was totally and completely RONG, I was totally shocked he knew so little about a/c....and in the RADIATOR business??

WTF?? I left it off to some ignoramus employee....

but did laugh at the same time....

:thumbs::bomb: