1968 Electra AC Problem

[Rod Frazier]

AC fully charged and compressor working, but minimal cooling.  Ambient temperature 78 degrees, air from vent 70.  System converted to R-134 some 20 years ago.  Never did work as well as it did with Freon, but better than it does now.  Any ideas?

[GARY F]

It sounds like it is in the vent position , not A/C. Are the baffles working properly?

[Rod Frazier]

1 hour ago, GARY F said:

It sounds like it is in the vent position , not A/C. Are the baffles working properly?

Baffles being the vent vanes?

[old-tank]

What are the high side and low side pressures and what is the temperature of the pipe coming out of the evaporator?

[JohnD1956]

You could try tapping the side of the expansion valve with the wooden handle of a hammer while the system is on. 

 

 

[Rod Frazier]

12 hours ago, old-tank said:

What are the high side and low side pressures and what is the temperature of the pipe coming out of the evaporator?

The low side is 34 pounds, but I don't have a way of measuring the high side.

[Rod Frazier]

11 hours ago, JohnD1956 said:

You could try tapping the side of the expansion valve with the wooden handle of a hammer while the system is on. 

 

 

I will do that.

[NTX5467]

R-134a systems are more sensitive to over-charge than R-12 systems are.  The amount of R-134a is usually about 10% less, as things end up, than for R-12.

 

The POA valve is what regulates evaporator temperature via pressure regulation.  Sometimes they can fail or stick.  Might try tapping it first.  Rebuilt POAs are out there.  The POA Eliminator item is to be avoided as it makes the system into a later-style Cycling Compressor Orifice Tube system.

 

If tapping the POA helps things, they CAN be adjusted.  In some years, the adjustment is on the inlet side, in other years it is on the outlet side.  Turn the adjustment screw 3/4 turn CCW and that should put the evaporator pressure about 1.5psi different from the R12 adjustment, and should result in cooling close to what the R12 system did.  I found a thread in the old www.ackits.com forum, back in the early 2000s.  That adjustment trick works for all GM systems, plus Chrysler EPR systems and Ford system which use the GM system in the later 1970s.  With age, the rubber in the valves can age and fail, but rebuilt POAs are now available.

 

That particular website is administered and run by some people in the AC profession in Arizona.  I found lots of interesting information in there, back then.  Forum posters who did the re-adjustment all claimed to get 40 degree vent temperatures in 80 degree F weather.

 

Enjoy!

NTX5467

[Rod Frazier]

22 hours ago, NTX5467 said:

R-134a systems are more sensitive to over-charge than R-12 systems are.  The amount of R-134a is usually about 10% less, as things end up, than for R-12.

 

The POA valve is what regulates evaporator temperature via pressure regulation.  Sometimes they can fail or stick.  Might try tapping it first.  Rebuilt POAs are out there.  The POA Eliminator item is to be avoided as it makes the system into a later-style Cycling Compressor Orifice Tube system.

 

If tapping the POA helps things, they CAN be adjusted.  In some years, the adjustment is on the inlet side, in other years it is on the outlet side.  Turn the adjustment screw 3/4 turn CCW and that should put the evaporator pressure about 1.5psi different from the R12 adjustment, and should result in cooling close to what the R12 system did.  I found a thread in the old www.ackits.com forum, back in the early 2000s.  That adjustment trick works for all GM systems, plus Chrysler EPR systems and Ford system which use the GM system in the later 1970s.  With age, the rubber in the valves can age and fail, but rebuilt POAs are now available.

 

That particular website is administered and run by some people in the AC profession in Arizona.  I found lots of interesting information in there, back then.  Forum posters who did the re-adjustment all claimed to get 40 degree vent temperatures in 80 degree F weather.

 

Enjoy!

NTX5467

Good info....I'll give it a shot.

[Rod Frazier]

Unfortunately, tapping on the POA and expansion valve didn't help --I never have that much luck!

[old-tank]

On 9/11/2023 at 7:45 AM, Rod Frazier said:

On 9/10/2023 at 7:39 PM, old-tank said:

What are the high side and low side pressures and what is the temperature of the pipe coming out of the evaporator?

The low side is 34 pounds, but I don't have a way of measuring the high side.

Get a gauge set and supply the answers to the questions above and we might be able to help you.  

[dmfconsult]

May be overly simple, but have you checked your vacuum lines going into the HVAC controls?  On my 67, there is a hub of 4 vacuum lines that control various aspects of the system.  Are any of those disconnected or split?  On the 67, they can be accessed from the passenger side of the engine bay at the firewall.  The heat on my 67 stopped working at one time, and the issue was simply that the vacuum line had become disconnected.  Here's a page from the 67 Chassis Service Manual that you can zoom into.  I would start with these connections.

 

Edited September 14, 2023 by dmfconsult (see edit history)

[Rod Frazier]

6 hours ago, dmfconsult said:

May be overly simple, but have you checked your vacuum lines going the HVAC controls?  On my 67, there is a hub of 4 vacuum lines that control various aspects of the system.  Are any of those disconnected or split?  On the 67, come can be accessed from the passenger side of the engine bay at the firewall.  The heat on my 67 stopped working at one time, and the issue was simply that the vacuum line had become disconnected.  Here's a page from the 67 Chassis Service Manual that you can zoom into.  I would start with these connections.

 

More good ideas.  And I'll try to borrow a gauge from my local mechanic tomorrow to test the high pressure.  Thanks.