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Charging problems

mjlinder on Thu June 11, 2009 7:01 PM User is offlineView users profile

Year: 1972
Make: Chevy
Model: El Camino
Engine Size: 350
Refrigerant Type: 134A
Ambient Temp: 89
Pressure Low: 10
Pressure High: 130

We just got our A/C system together and were attempting to give it a charge today. Here is the story so far -

Using a R4 compressor. Brand new parallel flow condenser from AMA. We were just at AMA a couple days ago to have all the hoses crimped. We also purchased a new receiver/dryer, and per their recommendation we removed the POA and replaced it with one of their POA eliminators. We put 6oz of oil into the compressor, and 2oz into the receiver. We put a vacuum pump on it and let it run for about 30 min (got to -30in/hg). Sealed it up and let it sit overnight and it was still at -30 this morning. Put the pump on for another 20 min, then started to charge. Also per AMA recommendation, we started with an initial charge of 24oz.

The initial charge got the low side pressure up to about 10, and the high side to about 125, measured with the engine running at 1500rpm. Vent temps were 68-70. Ambient temp was 89 measured right in front of the condenser. I started adding more 134, and the vent temps dropped to 65, with low side pressure at about 14 and high side at about 140. At that point , the vent temps started to climb, so I figured we were a little over full. I bled a little off, and the temps climbed even more. Right now we have low side pressure at 10, high side at 130, and 76 degree vent temps and cannot get it to improve.

Also, the system will not cycle. I had bypassed the low pressure cut-off during the charge process. When we shut everything down, both sides stabilize at 70. I plugged in the low pressure switch and we could not get the compressor to come back on. I pulled the plug back off the switch and bypassed it and the compressor cycled on.

We seem to have good flow over the condenser - the inlet is very hot (too hot to touch) and the outlet is just barely warm.

Could the problem be with the compressor?

Thanks!

Chick on Thu June 11, 2009 7:39 PM User is offlineView users profile

You are more likely undercharged.. At that ambient you should have a high side pressure of around 200 to 225psi (roughly).. Add more while watching the high side and "feeling" the lines.. The inlet to the evap should be about the same temp as the outlet, with the outlet slightly cooler.. Don't worry about cycling, the warmer it is, the less cycling you'll see.. Once it's fully charged you can test cycling by running low fan, at night, and once the evap temp is close to freezing it will cycle..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

mjlinder on Thu June 11, 2009 7:48 PM User is offlineView users profile

Thanks Chick. We will try adding more and see what happens.

I was thinking overcharged when the temps started to go back up. Also, it worried me that the compressor would not kick on unless I bypassed the low pressure switch, even with the low side showing 70 (where it stabilized after we shut it off).

I was also thinking compressor when we added more 134 and the pressures did not go up.

Onward and upward! We'll add more and I'll report back.

Mark

Chick on Thu June 11, 2009 7:57 PM User is offlineView users profile

Make sure the cycling switch is getting power, and it won't turn the compressor on until it sees around 21psi, even 25 on some... Just add a little at a time and let it stabilize, but you need the pressures higher at that ambient, and remember to feel the lines into and out of the evap...Hope this helps..

-------------------------
Chick
Email: Chick

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Freedoms just another word for nothing left to lose

mjlinder on Thu June 11, 2009 8:14 PM User is offlineView users profile

The switch is getting power. The compressor starts as soon as I jump the terminals on the plug. The compressor won't start even with >25 psi showing on the low side.

Chick on Thu June 11, 2009 8:59 PM User is offlineView users profile

could be a bad switch, but get the right charge in first, then check out the switch...

-------------------------
Chick
Email: Chick

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Freedoms just another word for nothing left to lose

mjlinder on Fri June 12, 2009 12:17 AM User is offlineView users profile

OK, looks like we are good, or at least closer. We put another 12 oz in for a total of 36 and still had low pressures and warm air. Checked the manual and the vehicle originally had a charge of 60 ounces! Figuring the 80% rule as a ballpark, that would put us at somewhere near 48. So in went another can. Temps and pressures were still low. I think the new condenser added a whole lot of capacity. Added another can, so we are at 60 ounces total (less a couple that I purged) and the pressures finally started to come up and the temps started to fall. Numbers are now as follows (ambient still around 89):

Idle-
Low 27
High 210
Vent temp 50*

1500rpm
Low 19
High 190
Vent temp 46*

We were out of 134, so we stopped there. I'm thinking about adding a couple more ounces tomorrow. It seemed that the pressures started to come up quickly towards the end of that last can. We took it for a drive and had vent temps down as low as 41, and the system was cycling on and off. Tested the pressure switch and it was shutting off at about 20 and on at just over 40.

Thanks for the help Chick!

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