My ACC seems to operate fine at low or moderate speeds. But when I get to highway speed, or if the RPM's are around 2000 or higher, I lose heat. Only cold air blows out. any suggestions?

sounds like your mono valve( heater valve) they sell rebuild kits for it. its located on the firewall, mine stuck on my way back from salt lake on a very cold winter day, good luck

How about the auxiliary water pump? When is it supposed to run?

when the heater is turned on or defrost

ok. thanks alot for your help. I've ordered a monovalve kit. After installing it, what is the best way to tell if the aux pump is running because when I checked in defrost and max heat modes it seems not to be running. can i simply disconnect it and apply 12vdc?

that will work, you don't here about them going out much, mine was a 83 and when I sold it last year it had never been changed with 260000 miles, good luck

make sure you put correct + - connections to aux heater.
This functions only to help deliver hot fluid at idle or when engine is off, not at speed, sounds like monovalve or vacuum issue.

thanks for the reply. it turns out the monovalve diaphragm is torn so I've ordered a rebuild kit. However, connecting power to the aux pump direct from the battery fails to turn the motor. Can the brushes be replaced on these motors or is it a complete replacement?

DICONNECT IT! if it does not hum when power is applied it is fried and can dammage you pushbutton or ACC control board. If it is not leaking, I would just leave it unplugged and forget it. If you are a pureist, however, a rebuild is not a common option. These are a PITA to replace as I am sure you have figured out. If you do be sure to put a 1 amp fuse in line to prevent burn out of ACC board should it fail again.

thanks for the reply. considering all the warnings i've read regarding blown ACC's , i disconnected it last nite. Luckily, when i tested it with a power supply it drew no current so i suspect that the brushes are gone or the motor windings are open. as far as being a purist... I AM. so i'll see if i can find a cheap replacement. the local parts wholesaler as one for $55. maybe i can repair it for less.

http://www.**************.com/store/item.php?item=123%20Vacuum%20Door%20Lock%20Advanced%20Troubleshooting%20and%20Repair

try this link for some good parts and troubleshooting info.