Only when the temp control is set to "heat." But the evaporator is in line all the time.

http://personal.utulsa.edu/~nathan-b.../4generald.pdf
http://personal.utulsa.edu/~nathan-b...g/25heater.pdf

 

Nice! Thanks for the answer.

I'm also considering just changing out the whole evaporator rather than cleaning the old one. Thoughts?

 

So I got the project done this weekend. I was amazed and how much crap had built up in my evaporator (pics below).

- After the swap, airflow was easily 3x
- The swap was pretty easy. I was worried that the evap would not pull out easily but it really does.
- Used a set of green HNBR o-rings
- I changed the AC receiver/drier at the same time.
- Going to get the system recharged today, hopefully it will be nice and cold.

As it was removed from the truck:


Removed from the housing:


Leaves cleaned off:


Just used a completely new unit, with the accessories moved over onto it:

 

Nice work. I think using a new unit was a good idea. The fins are fragile, and because of the bend are very difficult to clean inside.

 

Nice! Seeing the new unit makes me think mine was changed. I've got good air flow. What I've seen from socaltodd, rustbucket and scope makes me wonder though.

 

Hi guys, quick question what did you do about the conversion nipples that screw on to the r12 nipples? The only ones I've seen do not give enough clearance for the 134a quick connect couplings on the guages. Anyone know where to get some longer ones? Thanks
Al.

 

Got the system charged today, and it works quite well. 85F and 1000% humidity here in Atlanta (not there's not an extra zero!)

 

There are three kinds of conversion adaptors. The most common has it's own schraeder valve, so you need to remove the core from the existing fittings.

Ooops! That means you CANNOT use a gauge with R134a quick connect couplings to test an existing R12 system, because removing the cores would release the R12. But the good news is that the (nearly) least expensive gauges (Harbor Freight) come "natively" with R12 couplings, and R134a adaptors that connect to that.

Is that your problem? You have an R134a-only gauge set? There are conversion fittings that just screw onto the outside of the R12 connection, continuing to use the existing schraeder core. (And another kind with its own schraeder core that piggy-backs onto the R12 core.) But the ones RockAuto carries have their own core, and you remove the existing cores.

 

Mine has the fittings on the compressor, so I used a 90° on the low side and a straight short adapter, which uses the existing valve core on the high side. I was able to hook up my Harbor Freight gauge set.

 

Scope103 thanks, I did not know there were adapters to use r12 gauges with 134a refrigerant, am I understanding this correctly? I do, by the way have both sets of gauges.

 

In this set:
http://www.harborfreight.com/a-c-man...set-92649.html
The red and blue hoses have R12 fittings on the ends. The separate red and blue valves in the foreground of the case connect the respective R134a fittings to the R12 fittings on the hoses.

I've seen (on Amazon) cheaper gauge sets, but they did not include the R12-R134a connectors (easily available, but not free ) and no case.

 

I bought a "can tap and dispensing valve" at Autozone, here- http://www.autozone.com/test-scan-an...estid=11506161

and a valve for the service hose, here- http://www.autozone.com/test-scan-an...estid=11506897

The shut off valve is nice for servicing, between cans and to leak check after evacuation.

 

I don't need the valve on the service hose; my service hose has a schraeder valve, so it shuts off when removed from the can tap. But each gauge set is probably different, and without the schraeder valve in the service hose, you definitely DO need that valve.

 

Mine has a dual port, one with a schraeder valve. I could have capped the other, but decided I wanted more control. At least, I think I have more control!