68 Camaro underdash ac /heater box - Team Camaro Tech
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post #1 of 6 (permalink) Old Oct 1st, 17, 02:26 PM Thread Starter
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Eric
 
Join Date: Jun 2017
Location: Houston, TX
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68 Camaro underdash ac /heater box

I have been having trouble getting my ac to cool correctly. It's the first time I have put Freon in the factory ac system. I get cold air but just not real cold. It even seems like it gets warmer as the engine gets hot. Things I have tried to get this thing working
1. Changed compressor, POA, and Expansion Valve
2. Flushed system
3. Got the inside and outside air doors working properly
4. a) put valve in heater line; b) Disconnected heater lines completely.

Nothing has worked. Today, I recharged the system with only 2 cans of R12 to see if I could get this thing working. I also left the Distribution duct off the underdash ac box. This leaves an opening into the underdash box where the air comes out. With two cans of Freon the air is cold on the bottom side of the opening and hot on the top side of the opening. It is clear that the air on the top is unconditioned. The cold/hot door evaporator and heater core is working cause I can hear it slam closed when I move the controls to heater and back. Plus with the heater core is not getting hot water, this shouldn't be an issue. I'm stumped short of getting a different box or removing this one and trying to rebuild a second time. Any ideas as to what could be going on?
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post #2 of 6 (permalink) Old Oct 2nd, 17, 06:51 PM Thread Starter
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Eric
 
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Re: 68 Camaro underdash ac /heater box

Any way to check if the seal around the evaporator box is not sealing? Could it be a restriction in the evaporator?
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post #3 of 6 (permalink) Old Oct 7th, 17, 10:44 PM
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Steve
 
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Re: 68 Camaro underdash ac /heater box

What are your suction and high head pressures? Your suction (or low side pressure) should be at around 36 psi. Your high head will vary more based on outside air temperature, but around 180 psi. With only two cans of R-12, there isn't enough freon to fill your evaporator (hence the cold and hot). You may also have a POA valve not functioning correctly. Also the sensing bulb must be totally secured to the suction line and (immediately where it exits the evaporator case) totally covered with insulation. If any engine compartment heat can get to the sensing bulb, it will not tell the suction throttling valve to do its job. Let me know what you find!

Steve

'67 RS, convertible, factory A/C, 327/275 (M30), powerglide, parchment interior
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post #4 of 6 (permalink) Old Oct 8th, 17, 08:41 PM Thread Starter
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Eric
 
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Re: 68 Camaro underdash ac /heater box

I added 2 more cans of R12 this afternoon. Low was 34/35 and high was around 250. Outside air was at least 90 but probably warmer since my garage opens to the west so the sun was shining on everything, including me and it was hotter than hell. There was no frost on any of the piping. Still had warm air coming out of the top of rectangular opening and cold on the bottom. I'll let the ac sit overnight and check the pressures tomorrow after everything settles down. I will also reseat the bulb and add some extra insulation to be absolutely certain heat is not getting to it.

What about insulation between firewall and inside heater/ac box. Firewall around the top part of the box sure felt hot.I remember having trouble getting the pad to stay in place when I installed the box. Don't remember how I finally got the insulation between the box and firewall.
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post #5 of 6 (permalink) Old Oct 9th, 17, 05:25 PM Thread Starter
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Eric
 
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Re: 68 Camaro underdash ac /heater box

o.k. very interesting observations. Here's the pressures I observed. RPMs while observing was around 1500-1800 rpms. Outside temperature somewhere between 90 to 95 degrees F. Sight glass has some bubbles but mostly clear. This is 4 cans of R12. 10 oz of oil. A6 compressor. POA and Expansion valve. System was flushed prior to evacuation and adding Freon. New dryer. Evacuated for 2 hrs. Let sit overnight before adding R12.

- When I started the car for about 10 minutes - 30/150 psi
- once car warmed to operating temp pressures I observed 99% of the time - 32-38/240-250 psi
- periodically pressures spike as follows - 35-50/250-310 psi

The spike occurs within about 5 or 10 seconds. Stays at 45 to 50 psi for 30 seconds and then starts to drop. Not sure what's happening. Can also hear a drag on hp and rpms when spike occurs.

Almost feel like air or moisture is still in system. I could never get vent temperature below around 58 degrees F. But, it did seem like the temperature across the opening was more uniform.
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post #6 of 6 (permalink) Old Oct 9th, 17, 06:47 PM
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Daryl
 
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Re: 68 Camaro underdash ac /heater box

This may help.
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1968 Rally Sport
302ci
Muncie M22
Moser 12-bolt 4:10 posi
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