R-12/R-134a Conversion Advise


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Old 07-17-07, 03:09 AM
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R-12/R-134a Conversion Advise

'89 Tempo, 2.3L. Replaced ac compressor (leaking). Pressures are at 40 psig low and 190 psig high. System was evacuated and receiver replaced.

Cooling very well but the comp is in and out at highway speeds....approx every 10 seconds or so. I'm wondering if the low pressure switch is set too high for the 134. This switch was originally designed for R-12 and cuts out around 22 psig. Anyone have any ideas?
 
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Old 07-17-07, 04:32 AM
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Did you replace the orifice ? I wouldn't think that the low pressure switch should affect it. Sounds kind of like the condensor may be dirty.
 
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Old 07-17-07, 08:18 AM
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There are many components that need to be replaced in order to convert to 134. The compressor, sealers, orifice, consensor, dryer, etc. 134A has a higher operating pressure then R12. If these components are not change to a 134 spec, the system will leak.
 
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Old 07-17-07, 09:57 AM
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This Tempo has run 134 for about two years now....the compressor has always had an oil leak (front seal) but it got to the point where replacement was necessary.

I did not change the orifice and the car is cooling great but I am a little concerned with the compressor clutch coming in and out as often as it does at any speed over 60 mph. Thus the reason for asking about the press switch. The clutch has cycled this way since I've owned the car.

I'll keep running it and see how it does over the next couple of weeks before I turn it back over to HER. Thanks for the replies!
 
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Old 07-17-07, 10:43 AM
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The switches definetly needed to be changed when the car was converted.
 
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Old 07-18-07, 03:08 AM
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Thanks HotinOKC....I'm assuming I should use a switch for a model that would fit that is designed for 134? Would you happen to know what pressure(s) the switch will break at?

I cleaned the condensor last night mattison but it wasn't too bad.

Thanks again for "listening"!
 
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Old 07-18-07, 07:32 AM
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OK guys.....trimmed the refridgerant charge a little yesterday and I'm at 43 psig low and 190 psig high at ambient of 90 and interior at 110.

The compressor is in and out at approx 10 second intervals. The pressure switch is the original and this system was designed for R-12. It appears to me the press switch is breaking early (22 psig) but I can't seem to find the spec on make or break points of the switch.....can anyone share this info with me?
 
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Old 07-18-07, 08:08 AM
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Not sure of the psi specs on the switch, but you can bypass the switch by jumpering it and se if the compressor stays on. Take a paperclip or similar and stick it in the A&B terminals of the switches wire harness connector.
 
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Old 07-18-07, 09:02 AM
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Ok Hot....thanks. I think I will jump the switch and try for a day or two....at this point, it may ruin the compressor but as it is SHE won't drive it anyway. I'm assuming the switch (at the receiver) is for low pressure only. Since we're on the topic, is there a high pressure switch or is it incorporated into the low press(?) switch?
 
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Old 07-18-07, 09:11 AM
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Well, on a typical 134A system, there is a highpressure switch and usually the low pressure is integrated with the compressor and cannot be changed.

Your car came initially with one switch, it is often called the "cycling clutch switch" which is probably the one you have.

In a correct 134a retrofit, all these components would have been changed.
 
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Old 07-18-07, 09:24 AM
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I hear ya! I didn't replace anything but the comp and dryer since this is HER beater vehicle.

We have several other vehicles with working ac but I would rather her commute in this thing....provided I can get the ac going again.

I guess, other than losing my pressure protection, It can't hurt to run it a day or two with the switch bypassed....right?

Thanks again for all the replies!
 
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Old 07-18-07, 10:22 AM
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No, it shouldn't hurt it.
 
 

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