Earlier I asked about a R12-R134 conversion. That is behind me as refrigerant is no longer a concern. I was made aware that either the control unit (control panel/box on dash console?) or the "Fan Mix Motor" would be likely culprits as both are reputed to fail on this vehicle ('90 NA). System blows warm air w/ slider all the way at blue and AC on. Gets cool at night at freeway speed. Constant, substantial heat from under the dashboard, with the windows rolled-up it gets uncomfortably warm fairly quickly, even with climate control 'off'.

Will replacing the control fix the problem, or is it the fan mix motor (?), and how hard is it to replace?

 

There is always going to be warmer than ambient air coming out of the vents, even if the damper on the air-mix motor is working properly. Add in the substantial heat from the transmission tunnel, the firewall and the exhaust radiating on the underside. The car will just tend to be warmer than ambient temps.

Since you are no longer worried about the refrigerant, does this mean you have verified that the refrigeration part of the A/C is working correctly?

Try verifying a couple of things. Here are some diagnostic tests:

First try pinching off the heater line. Use some channel lock pliers. Don't smash the line so tightly that you damage it, but smash it to the point that no coolant can flow through the line. Now drive the car till it warms up. See if the air is *substantially* cooler with the line clamped shut. Now remove the vise grips and check to see if the air is suddenly warmer. This test will tell you if you are leaking hot air through the system. If the temps are pretty much the same, clamped or unclamped, then the door is correctly sealing.

Also, try this test:
Step 1.) Turn the A/C on and let the car idle. Verify that the A/C Compressor is turning. Set the A/C to recirculate. Now set the fan speed on low. The large A/C pipe should get really cold and sweat profusely. If it does not, then the A/C has little to no charge. If the pipe gets cold, go to-

Step 2.) Turn up the fan speed from low to high. Wait for 4-5 minutes. The pipe should still be cold. If the pipe is cool but not cold, the refrigerant charge is low. If the pipe is not cold, the refrigerant charge is very low.

Good Luck!

-Jack

 

Heh, cue the screaming monkeys, the compressor won't even turn. Bit hard to cool the system without the refrigerant circulating...(@Jack, did the second test, AC compressor never engaged).

 

Another test to see if the charge is low: There is a pressure switch on the AC system to prevent the compressor from engaging if the charge is low. I think the switch is somewhere near the receiver/drier (been a while since I looked). If you jumper that and switch on the AC, the compressor should engage. Don't let it run for very long like this though.

 

AC pressure is critical
Hopefully this week I get the pressure right in my car and have fully operational AC once again since my Frankenstein combo of AC components in my car seems to be tricky to get right

 

Hey Rob-

Are you doing R134a?

 

yes, last year we were dealing with the wiring more then anything, then we never got the pressure right. We gave up on it and I was going to do it over the winter- you know how that goes, lol

 

Rob u need gauges? cuz I bought a set, fixed my AC (thx to jackhild59), and now its collecting dust. I also have the vacuum pump and stuff.

 

i actually have the whole ****, thanks though

 

I'll try that tomorrow (technically this morning). Advanced Auto's getting the master cylinder I ordered in. Getting interesting bringing her down to a halt (JK). Before learning about the Ac systems I did buy a 134 recharge kit and a set of conversion fittings. The recharge kit came with a pressure gauge, what pressure should the R12 be at?

 

It depends. The temperature and pressure are proportional. This is why it is best to charge in the correct weight of refrigerant.

http://www.rogersrefrig.com/Pressure...e%20Table.html