1972 Monte Carlo freeze up issue

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fish504
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Joined: Sun Jun 11, 2017 11:28 am

1972 Monte Carlo freeze up issue

Postby fish504 » Sun Jun 11, 2017 11:39 am

Trying to bring my old car's AC back to life. To date we have replaced the relay switch, dryer, thermal limiter fuse, POA, and expansion valve. System was vacuum and leak checked. Charged with 3.25lbs of R134. When u initially turn the ac on Max it cools nicely at the vents for up to 30 seconds. Then the air turns warm. There is icing on the evaporator inlet. Any thoughts?
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bohica2xo
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Re: 1972 Monte Carlo freeze up issue

Postby bohica2xo » Sun Jun 11, 2017 12:09 pm

What are the system pressures?

What pressure is the POA valve calibrated at?

Where is the TXV sensing bulb & how is it attached?
fish504
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Re: 1972 Monte Carlo freeze up issue

Postby fish504 » Sun Jun 11, 2017 2:34 pm

Mechanic didn't tell me the pressures. He said they were odd and that there might be a blockage. That was the end of Friday, supposed to take another look at it this week, but honestly the shop is totally unfamiliar with a POA system. POA pressure not known to me right now. Supposedly set up for R134 use. Bulb is at approx 3 oclock position held with 2 factory clamps. Covered with insulation.
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bohica2xo
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Re: 1972 Monte Carlo freeze up issue

Postby bohica2xo » Sun Jun 11, 2017 4:24 pm

The frost on the TXV discharge is normal. OEM they were covered with Presstite Tape where exposed in the engine bay. You should do the same.

POA systems should have a constant pressure on the evaporator side of things. Many systems have 2 low side ports - and the port between the POA & the compressor will show different pressures - even vacuum is possible.

The high side numbers are important as well.

POA systems need a couple of tests. The POA setpoint can be determined by disconnecting the cabin blower & idling for a few minutes. The evaporator pressure should remain constant at the POA setpoint.

Next is the full load test. Cabin fan on highest speed. Both Doors open. Run engine at 1500 to 2000 rpm for 90 seconds, then record pressures while at that rpm. Record ambient temp & vent temp too.

Gather that data up & get back to us.
Dougflas
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Re: 1972 Monte Carlo freeze up issue

Postby Dougflas » Sun Jun 11, 2017 4:31 pm

TXV looks bad. Pull bulb loose and hold in your hand. Pressures must change. Bulb may have lost its charge or the TXV screen is plugged.
fish504
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Joined: Sun Jun 11, 2017 11:28 am

Re: 1972 Monte Carlo freeze up issue

Postby fish504 » Sun Jun 11, 2017 4:56 pm

Thank you, I'm meeting another mechanic tomorrow and hopefully he is more knowledgeable on the POA.

The TXV is new and it makes sense that it might be blocked at first run up. I know the system was not flushed.
Dougflas
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Re: 1972 Monte Carlo freeze up issue

Postby Dougflas » Mon Jun 12, 2017 12:27 am

Monitor the low side with the engine at 1200 to 1500 rpm, remove the blower motor hot lead. The POA should be at 26.5PSI for R134 and hold it . If you look in the "tips and procedures" section, I remember putting a tropic on testing the TXV. It may be in the testing of an EPR but it should be there somewhere.

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