How do you monitor the performance of your A/C system? Clock / VDO Temp Gauge Swap.
 

The poorly designed primative A/C systems in our cars require careful monitoring of vent temps and compressor cycling frequency to avoid evaporator freeze ups particularly in high humidity conditions. To avoid this, the compressor must cycle off either automatically via the temp dial setting or manually by monitoring the vent temps and peroicically turning the dial down to periodically get the evap core temp above freezing.

I monitor the vent temps and compressor cycling via a digital thermometer permanantly mounted in the center vent which works well but I would like a cleaner look to the dash so I am considering ditching the clock which I rarely use in favor of a VDO Outside Temperature Gauge 397-154 (F Scale) with the temp probe mounted in the bowtie outlet. Although I would prefer a digital readout the VDO gauge dial has an easy to read mark at 32 degrees and with 50 degrees at TDC anything to the left of the 12:00 o'clock position via a quick glance will indicate good performance.

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Gauge Source: New Page 1

The plan will be to run the sensor wire up the bowtie recirculate hose that I installed this summer into the bowtie outlet so that the probe will be near the evaporator.


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Recirculate hose project details here: I would only recommend considering this if you have the large dash vents coupled with the evap fan motor upgrade otherwise the loss in air volume through the vents would result in an overall degrade in system performance. The idea here is to recirculate pre-cooled air back through the evaporator reducing the differential of incoming air to evap core temp thereby lowering vent temps further & faster that without.

http://forums.pelicanparts.com/porsche-911-technical-forum/484220-new-idea-help-lower-c-vent-temps.html

Could not tell from VDO or source's website if the gauge had a bulb.....here is the response to my email. I did not want to do this is the gauge is not lit.

"Thank you for your inquiry! The gauge comes with a clear bulb but it also can be made to light red or green with the optional VDO bulb covers."

Temp Gauge too small to mount in clock opening without it looking cheezey so I mounted it under the dash. Temp sensor probe is mounted in the PVC elbow coming out of the bowtie outlet.

Made a clock delete out of 3" PVC fittings and a electrical box cover to mount the 2 1/16" temp gauge but it looked like crap so I scrapped the idea.

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Mounted it under the dash instead

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With gauge lights on.

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I keep it simple............

Along with an LED wired in parallel with the condenser fan motor hidden next to the ashtray.

Also, a 10 degree on/off window/cycle on the compressor prevents evaporator freeze-up.


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This summer which has been exceedingly hot and humid I have been running my system at about 2 o'lock on the temp setting dial to promote frequently on/off cycling and avoid freeze ups. For the first time ever whlle in a recent traffic jam in Charleston at 96+ degree ambient the H/L pressure switch cut the compressor out to avoid high pressure system failure - vent temp shot up pretty quickly. Everything normalized when I started moving again and had good airflow over the condensers.

If your thermostatic temperature control switch/sensor were working properly it would open the compressor clutch circuit at 34F evaporator core temperature and not close it again until the evaporator core temperature rises to ~37F.

I was going to say that if I feel a little breeze from the side vents , I know the front fan is helping circulate the cabin air - but I see you boys are serious about your A/C. When I was a lad , dad just drove a bit faster when it got hot. I must get up to speed.