A/C Sytem question

[hatzie]

The little 1.5CFM Robinair Vacustar pumps work fine they just take longer.

Envirosafe used to claim you could charge a system using their hydrocarbon blend without a vacuum... Not a good idea.

[gmachinz]

Yeah-I am not sure what to think about some of the newer alternative kits out there...I've never had issues with the 134 as it is so I'm reluctant to try anything else-a creature of habit on some things I guess you could say...lol

[hatzie]

There are conflicting reports on what is EPA legal for alternatives. R134 is safe and conservative.
I've used Envirosafe ES12 and straight HC-290 with a tiny bit of R600a. I charged according to the Jungle Eddy "How to charge an AC" procedure. Hydrocarbon blends are not for everyone but the explosion and fire hazards vs the various DuPont refrigerants are way overblown IMHO.

[LEEVON]

Just to add a little to the already great discussion, there is one thing the DIY'er usually does not have access to and that's a refrigerant recovery machine. Pressure gauges tell most of the story but they cannot precisely measure volume. The volume of refrigerant can be critical. Pressure is always influenced by temperature and other factors such as air movement across the condenser which can't be precisely controlled. But when the volume of refrigerant that the system is designed for is measured, the variables are less important. That's why we use a calibrated recovery machine in the shop, because it takes the guess work out.

It's highly likely that a system charged with pressure readings alone will be off a few ounces in either direction, which does not seem to make a huge difference on some vehicles, but for others (particularly newer) the volume of refrigerant is make or break. As little as 8 ounces can make a world of difference in vent temps. So if there is ever any doubt, have your system recovered (weighed) and re-charged with the designed amount, you may be surprised at the results.

Another tip, if you're having trouble getting your high side pressure where it should be and it's taking FOREVER, grab a hose and spray down the condenser or keep a fan aimed on it. The hose works great when you're in your driveway and it's 85 degrees. This will pull the remaining refrigerant into the system. Let it stabilize and take readings again.

[Troy 82]

gmachinz: 80-90 on the High side? Charging by the gauges can & is always done. Yes just a few ounces like he said can make a difference. Yes charge by weight if your using the original refrigerant the system calls for r12 134. On a retrofit you don't know what the charge amount should be so we go by the pressures.

[Keith Seymore]

Do we as a group have concensus on what the scaling factor should be?

(ie, R134 = .85 R12, or whatever)?

K

[Just call me Sean]

Yes the retrofit instructions call for 85% of R12 capacity.

[hatzie]

Recovery measurement only works if the system was still charged. If the condenser was punctured or there was another leak then all bets are off unless the machine can extrapolate air removed to volume needed.

A fellow with the handle Jungle Eddy posted some instructions on successfully charging non OEM refrigerant on one of the AC boards back in 2001. It was in the Hydrocarbon HC-290 R600a and blends discussions... but it has always allowed me to get consistent decent vent temps with whatever refrigerant I used regardless of the original refrigerant.

I posted it in another AC thread. http://67-72chevytrucks.com/vboard/s...48&postcount=6

[Keith Seymore]

Ok - back in business. We'll see how it goes over these next few days.

Originally Posted by hatzie

Not adjusting the LPCO switch and not properly adding a HPCO switch to the high side are next in line. These will save your compressor when the system charge isn't perfect.

Can we have some discussion about how this is done?

K

[hatzie]

LPCO is the low perssure cutout switch.
It's installed on all of our A/C systems. The adjustable LPCO switch went obsolete in the 90's. There is a screw between the terminals that allows you to raise or lower the switching pressure. LPCO has 2 functions. It needs to be set high enough to prevent freezup of the Evaporator while not cycling the compressor so much it's not cooling. It also prevents the compressor from running with zero charge. 20-21PSI is a good place to start.

HPCO or High Pressure Cutout or Discharge Pressure Cutout.
Was only installed through @1978 squares with the older TXL (Thermal Expansion Valve) AC systems. It was re-introduced sometime in the 90's when R134 became the refrigerant of choice. The Orifice valve systems in the 79-91 squares don't have a HPCO. It can be added to the compressor head if you've updated to a Sanden compressor. It's also possible to add it using a saddle clamp fitting or brazed fitting close to the compressor in the high side hose assembly. It's wired in series between the LPCO and the Compressor Clutch. It's used to shut the compressor off if head pressure rises to a dangerous level. I used the stock GM HPCO that was already on the compressor from the 6.5L donor truck.
It's worth noting that Dangerous head pressures are dependent on the refrigerant you use. You'll have to look this info up or just buy a new HPCO for a truck that you know uses R134a.

[Just call me Sean]

I just charged mine and am getting about 53 degrees at the vent moving or sitting still. Do you think lower temperatures would be possible if I adjusted the low pressure switch? I don't remember what pressure it was at.

[gchemist]

Irish1941,
I'm interested in part numbers. I have to discharge my R4 system to replace a bad high pressure switch. I might as well convert over to a 508 and be done with it. I may have to bend a new fuel line. Hopefully my RPM Air Gap heater hose does not get in the way either. I can move the heater hose to another further out port. I would like to see rear view pics of a 508 mounted with R4 hoses.

[Keith Seymore]

Originally Posted by hatzie

LPCO is the low perssure cutout switch. ...etc

HPCO or High Pressure Cutout or Discharge Pressure Cutout.
...etc.

Thank you; I'll bust out the gages and see what I've got.

I'm getting some cycling, otherwise similar performance to what I had prior to the compressor failure.

We are experiencing some unseasonably low ambient temperatures (highs in the low 70's) so I'm not sure what affect that might be having on all this.

K

[Sodell]

I wish I could borrow Hatzie for a day! He gave me good info on my install.

[Keith Seymore]

Just checking back in to say it's going great.

We are finally getting summer here, with ambients in the high 80's and low 90's. Humidity is unbearable.

I am running around in "Norm" with the fan on the second or third setting and quite comfortable.

I think we can consider this a success at this point.