Temp at dash outlets with A/C

[Steve C]

Superformance guys,

Would appreciate if someone who believes their A/C operates OK would conduct a simple test for me.

I'd like to know what the dash outlet temp is under the following conditions:

A/C switch on, Recirc off ( recirc switch light off and sure outside air coming in through the NACA vent), all air out of dash ducts (not floor or demist or a mix), engine at 2,000RPM, and fan blower on lowest speed.

I'm getting 52F but, am told should be 40F or so.

My elex all working OK and Freon charge seems OK so only thing I haven't tackled is adjusting the thermostat. Has anyone set up their own A/C and if so did you adjust the thermostat and what proceedure did you use?

Thanks, Steve P2125

 

[DaveM]

Steve,
I get 50degrees at the vent with recirculation. That was with 70 degree ambient, car not moving, and front hood up. On 90 degree days 57 degrees at vent. I don't know that the thermostat (near the evaporator) is adjustable and not sure that is a problem anyway. I'm not real pleased, but am not sure I have correct charge amount. Long story that started with an A/C shop not detecting factory o ring leak, me wasting $200, etc. Finally bought a vacuum pump and gauges myself. Have worked at insulating cabin rear window and tunnel leaks. Maybe others can chime in with temperatures.

 

[Dimi Terleckyj]

A/c temp should be initially set at 10 degrees C which is approx 52 degrees F.

Temp measurement is taken with temp probe sitting in the outlet vent of the dash.

Dimi

 

[Steve C]

Dave M and Dimi,

I'm measuring 52F at dash outlet with digital thermometer when car first started and maintains this at nights but after about 1/2 hour in day temps of mid 80's and with sun load the dash air blows warm (no longer 52F).

Elex OK, charge seems OK or I wouldn't get 52F as described above but, why is it blowing warm after 1/2 hr of driving with external heat load. Isn't the thermostat supposed to control the compressor clutch on/off and in doing so compenate for the heat load but, if I'm getting 52 as described at night then the thermostat is set OK?

If I was getting coil freeze up there wouldn't be air flow but, there is (by the way what can cause freeze up other than no air over the coils?).

The elec circuit is: A/C switch to low press switch (protection for loss of freon) to thermostat to compressor clutch relay and I hear the clutch cycling on/off even when I get warm air blowing as described above.

The SPF thermostat is adjustable so is it just a matter of adjusting to increase the on time of the compressor clutch but, won't that lower the 52F I'm getting at the dash outlets as described ??

I'm confused.

Any suggestions?

Thanks, Steve

 

[Jack Houpe]

Steve on my last trip I took an IR hand held meter, on the left hand side in recirculation I measured 48 F on high and slightly higher on the right hand vent. I have insulated the foot well area and the engine fire wall best as possible but still seem to get a high reading (96 F)on the meter when the car is cruising on these areas. One thing I did do that was recommended by Mike Trusty is put the foam pipe insulation on the low side from the AC unit all the way back to the compressor. I pulled the foam spacer in the front of the car and split the foam and slid it back to the other (rear) foam spacer. Perhaps this helped with the lower reading at the dash. Also the temp dropped to 45 F when the fan was on a lower speed. If you can beat the heat soak from the radiator and the engine I think it will do a great job. I am still working on that. I also read 35 psi on the low side of the compressor which is about 40 F according to the gage at the evaporator. @1500 rpm
If I was getting coil freeze up there wouldn't be air flow but, there is (by the way what can cause freeze up other than no air over the coils?).
Not enough freon, remember the lower the pressure on the low side the lower the temp of the evaporator, freezers in our homes operate at 1-2 psi on the low side, this is confusing but the more freon the higher the temp at the evaporator, the trick is to keep is close to the freezing point but just above so the evaporator will not freeze. Look at your low side pressure with about 1500 rpm on the motor.

 

[Steve C]

OK, just did a little research and condition I describe above (intermittant cooling) could be caused by air or moisture in the system allowing ice to form and block the orfice tube (still pass air over the coils) requiring a purge and recharge.

You guys agree?

Jack,

Good idea re insulating the low side pipe in the tunnel (I'll do it). I seem to be OK temps in the footwwell and not bad from the rear (have insulated glass and firewall insulation already but, sun load is bad. I think I'll be OK if I can maintain 45 tpo 48 like you.

Thanks

Steve

 

[Jack Houpe]

Steve if you have a AC vacuum pump then remove the freon and then pull a vacuum on the system for several hours if not all night, recharge oil and freon, that should get rid of water in the system. That will fix it but you can see if that is the problem by looking at the high side pressure on the low and high side while above idle.

Mike recommended to to all the lines (radiator, heater and AC high and low) but said that the low side is most important.

Good luck my friend wish you were a closer.

 

[Jack Houpe]

That will fix it but you can see if that is the problem by looking at the high side pressure while above idle, it will get high. Typing is not my bag.

 

[DaveM]

Jack,
Do you recall approximately how many oz. r134a you used? Thanks.

 

[Steve C]

Dave,

Per Olthoff's guys: 2.25#

Steve P2125

 

[Jack Houpe]

About 2.5 cans, I did not weigh the last can when finished. Look at the low side pressure @1500 rpm and when it get to about 35 psi stop filling. On my gages you will see the evaporator temp just above the low side pressure, if you can get it between 35 and 40 degree F you are in the the sweet spot.

 

[Dalton Veitch]

Pumping down and pulling a vacuum on the refrigeration system allows the moisture in the system to boil off (at the low pressure). With an extensive hose/piping system as on rear or mid-engined cars, you want to hold this vacuum for two or three hours to be really sure you have got rid of all moisture throughout the system, presuming you have leak tested it first.
Then you can put the refrigerant charge in and get optimum performance. The optimum usually takes trial and error (ie. the weight of refrigerant to add), to get as low a temperature as possible out of the evaporator outlets at the dash, while not having the compressor continually tripped out on the low/high pressure cut-out.

Dalton