Any AC Techs

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bobscuda67

bobscuda67

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I changed over my RV-2 compressor to r134 along with the rest of the system.
I charged it yesterday and have high readings on the gauges. Low side is 50 and the high side is 250 at idle. I only put 24 ounces of refridgerant in it and it calls for 42 onnces of r12. I'm way below the 85% recomended amount.
At idle the vent temp was 55 degress, ambiant temp was 93 with 87% humidity, and driving the car it came down to 48 degress.
Should I quit here and call it good, or is there more to be had?
 
Here is the pressure chart for R134:

Low Side High Side
85F 45 to 55 PSI 135 to 155 PSI
90F 45 to 55 PSI 250 to 270 PSI
95F 50 to 55 PSI 275 to 300 PSI

R134 runs at much higher pressures than the old R12. It looks like you could add a little more to get the high side up to 270 or so. Did you change out the oil? It will gum up if it is the R12 type of oil. Your vent temperatures look good though, and that is without recirculating the air.
 
what system are u running. year stuff like that? is it cycling on and off or just running. did you spray water or the connenser when it was running? warm your cans a little when installing don,t boil them just set them in hot water.
 
with r12 gas pressure equals temperature within a few degrees. A few more degrees difference with r134. The r12 systems aren't built to handle the pressures required with 134 thus the " less gas charge " solution.
I think if I did anything I would let just a tad of gas out of yours. If the high side falling to about 225 will let the low side down to about 46 you're set. If you have a very small leak somewhere ( who doesn't ), leave to lower itself.
 
System was fully flushed and the compressor was dissassembled and all new seals installed. Filled with PAG 100 double end capped oil. The condenser is new also.
I did not spray water on it. Being an 67 system there is no cycling switch, so it just runs till the evaporator freezes. All temps were with MAX ac setting.
When the gauge readings were at 40/225 the vent temps were at 75 degrees at idle. At that point I had only put in 12 ounces of r134. Put in another 12 ounces and that is where it's at now.
 
Having done multiple conversions especially on older vehicles you may need to add an electric fan to bring down the pressures. You stated that at idle they were both high but above idle they were lower, that is telling you you may need more air across the condenser, adding a pusher fan in front will remedy your problem
 
A rough estimate is the high-side should be about 2.2-2.5 times ambient temperature. So if it's 90 deg out, the high side should be between 198-225, and that's with the engine running about 1500 rpm's. My .02
 
bobscuda67 said:
Being an 67 system there is no cycling switch, so it just runs till the evaporator freezes.
Click to expand...

Wrong. All A-body A/C systems thru '73 had clutch cycling switches. They were adjustable via the temp slide lever thru '72, fixed in '73, eliminated (replaced by EPR valve) in '74. If your system hasn't got a clutch cycling switch, you need to add one.
 
slantsixdan said:
Wrong. All A-body A/C systems thru '73 had clutch cycling switches. They were adjustable via the temp slide lever thru '72, fixed in '73, eliminated (replaced by EPR valve) in '74. If your system hasn't got a clutch cycling switch, you need to add one.
Click to expand...

I'll have to look into that .
 
I converted a Ford Ranger years ago. I put a fan on the condensor and a high pressure cut off switch in it. It was explained to me that during extended idleing the pressures could climb causing issues. Truck idled for over an hour and pressure did not move, so I think the pressure switch was a waste. My vent temps were in the high 20's -low 30's in the heat of summer in AZ....
 
I wouldn't give it a second thought 134 runs higher pressure than R12. also, it does not have the good cooling qualities at idle in some instances as R12. I would simply charge it with the recommended amount and call it a day. Not uncommon for high side pressure to exceed 300 when it's hot out. i still do A/C work for friends, church members and family as Im still A/C certified.....not that that means much, but I've done a lot of A/C work and your situation sounds pretty normal to me. As stated previously, if you do not have a cycling switch, you certainly need one.
 
I was driving the car Sunday and the ac compressor quit along with the fan. Check the fuse and it was good. Took the dash apart to get at the vacuum switch. Tried to test the contiunity and it's dead. Orderd a new one from NAPA, and it will be here Thursday. Checked the fan resistor and it was ok.
Since I have the dash apart, where would the cycling switch be located? I don't see anything on the air box, unless it's on the back side.

I hate working on anything behind the dash! It has to be the worst.
Thanks for all the help.
 
The clutch cycling switch in the '65-'72 factory heat/AC system is controlled by the temperature slider lever (which also operates one of the air doors on the heater box). Find what moves on/near the box when you operate the temp slider back and forth. The clutch cycling switch has a small-diameter copper sensor tube buried between two fins of the evaporator, so that's another way you can find it. But it sounds like yours might be missing.
 
If all above checks out then the compressor reed valves are the problem. At 50 psi low side pressure your vent temps are going to be around 52+ degrees. Is it the original "A" boby compressor? If it is off anything other then an "A" body there is a EPR valve in the compressor and that would be a problem.
 
Lots of good info here. You did good to rebuild the system before you converted it. If your system cools that good with that high of ambient temp. I would say you're good to go. If it's 90 outside and the duct temp stays constant after idling for 10-15 minutes you shouldn't need a electric fan. Right or wrong it's working good.....drive and be cool. MIke
 
Just because "it's blowin' cold" doesn't mean it's "good to go". An undercharged system can blow as cold as a witch's teet in December and ice up the evaporator.
 
The pressures are good and the temperature drop from ambient is good also. He charged it with less than 80% of the recommended R12 charge. I don't see anything that would cause a problem unless you have a control problem which according to your earlier post you might have. A electric fan will help lower the pressures and duct temp at idle and slow speeds. Mike
 
slantsixdan said:
The clutch cycling switch in the '65-'72 factory heat/AC system is controlled by the temperature slider lever (which also operates one of the air doors on the heater box). Find what moves on/near the box when you operate the temp slider back and forth. The clutch cycling switch has a small-diameter copper sensor tube buried between two fins of the evaporator, so that's another way you can find it. But it sounds like yours might be missing.
Click to expand...

Found it Dan! I traced down the cable and it is attached to a bellcrank lever, by the blower motor resistor, and goes back to the left side of the radio. If it works might be a different story.
Also, my car does not have a heater control valve on the inner fender, like other cars I've seen. Did some cars not come with them, or do I have to start looking for parts for that too? It has 3 vacuum lines but no mounting holes on the inner fender.
 
It may not have been mounted to the fender. I have seen some water control valves that just go inline on the hose and no mounting hardware. Dodge vans are like this.

Every Mopar a/c vehicle I have seen has had a water control valve.


Chuck
 
slantsixdan said:
Nooooo…an overcharged system would flood the evaporator, making cooling less effective (and thus making a frozen-up evaporator less likely).
Click to expand...
Right you are Danno' An undercharged system will freeze up. My original comment was for Bob's original post about whether he needed to add more freon and as usual things got out of hand. Thanks for your knowledge Dan. Mike
 
bobscuda67 said:
Found it Dan! I traced down the cable and it is attached to a bellcrank lever, by the blower motor resistor, and goes back to the left side of the radio. If it works might be a different story.
Click to expand...

Sounds like not from what you're describing (freeze-up). You should be able to hear it click on and off loudly. You can test it by removing it, putting a bunch of ice in a tall drinking glass and filling it up with cold water , sticking the sensor capillary tube into the ice water, and working the switch lever back and forth through its range of motion. No click = no work.

Also, my car does not have a heater control valve on the inner fender, like other cars I've seen.
Click to expand...

Each and every '65-'76 A-body with factory air had a heater valve on the RH inner fender. Perhaps yours went away in a previous crash repair or something. The '65-'69 models used an unsprung valve with 5/8" inlet and outlet; the '70 models used an otherwise identical valve with 1/2" inlet and outlet. These valves use a double-acting vacuum pot serviced as a separate component (not included with replacement heater valve: vacuum applied to one side of the pot opens the heater valve, vacuum applied to the other side closes the valve. The '71-up models use a valve spring-loaded open, with an inbuilt single-acting vacuum pot: applying vacuum closes the valve. 1/2" in and out 'til the middle of '76 production, 5/8" in and out til the end of A-body production. The '65-'69 valve is this one. Spendy, and you'd still have to find the double-acting vacuum pot (also spendy as NOS, tough to find as a working used part). The heater valve should be closed when A/C or Max A/C is selected, open when Heat or Defog is selected. It would not be difficult to alter the vacuum hose setup and retrofit the late -'76 spring-loaded valve so that it would work correctly on a pre-'71 application like yours and I just happen to have one, a newer-design part that doesn't bolt to the fender (small enough and light enough weight that it just goes in the heater supply hose and hangs in space) I can't use on my '73 which has 1/2" heater supply hose, not 5/8" like your pre-'70 and the late-build '76s, brand new in box, for a great deal less money than the NOS '65-'69 valve linked above. Send me a PM if you'd like it.
 
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